food safety engineering: an emergent perspective
TRANSCRIPT
Food Safety Engineering: An Emergent Perspective
A. Lopez-Gomez Æ P. S. Fernandez ÆA. Palop Æ P. M. Periago Æ A. Martinez-Lopez ÆF. Marin-Iniesta Æ G. V. Barbosa-Canovas
Received: 23 January 2009 / Accepted: 23 March 2009 / Published online: 14 April 2009
� Springer Science+Business Media, LLC 2009
Abstract In general, food engineers are trained to solve
engineering problems in the food industry. More specifi-
cally, the food engineer must specify the functional
requirements, design, and testing of food products, and
finally, the evaluation of products to check for overall
efficiency, cost, reliability, and most importantly, safety.
Food safety must be considered foremost as the overall
engineering problem encountered in the food supply chain,
and it must be solved from a food safety engineering per-
spective. This article will show that the food safety engi-
neering perspective is needed in order to produce high
quality food products (minimally processed) that are both
safe and secure. This multi-disciplinary approach will
involve certain engineering components: (i) predictive
microbiology as a tool to evaluate and improve food safety
in traditional and new processing technologies, (ii)
advanced food contaminants detection methods, (iii)
advanced processing technologies, (iv) advanced systems
for re-contamination control, (v) advanced systems for
active and intelligent packaging.
Keywords Food safety engineering � Food engineering
Introduction
Food Safety: An Increasing Concern
Within the past decade, food safety has been an increasing
concern for consumers, retailers, and all production and
processing areas of the food industry. Food safety is also of
crucial importance to a nation’s economy and health sys-
tems. Calculation of annual cases of salmonellosis and
campylobacteriosis shows that the yearly number of cases
in Europe is likely to exceed five million [93]. An esti-
mated 25–81 million cases of foodborne illness and an
estimated 9000 deaths are associated with consumption of
contaminated foods each year in USA [34, 76]. Even
though an economic value can never be assigned to lost
lives, the USDA’s Economic Research Service [62] esti-
mated that each year in the United States, five foodborne
illnesses—Campylobacter spp., Salmonella spp., Esche-
richia coli O157:H7, Listeria monocytogenes, and Toxo-
plasma gondii—cause $6.9 billion in medical costs, lost
productivity, and premature deaths [103]. In 2006, it was
estimated that foodborne diseases cost the economies of
England and Wales slightly less than £1.5 billion [73].
A. Lopez-Gomez � P. S. Fernandez � A. Palop � P. M. Periago
Food Engineering and Agricultural Equipment Department,
Technical University of Cartagena, Cartagena, Spain
A. Martinez-Lopez
Associated Unit: Technical University of Cartagena—IATA
(CSIC), Burjassot, Valencia, Spain
A. Martinez-Lopez
European Food Safety Authority (EFSA), IATA (CSIC),
Burjassot, Valencia, Spain
F. Marin-Iniesta
Faculty of Veterinary, University of Murcia, Espinardo, Murcia,
Spain
G. V. Barbosa-Canovas
Center for Nonthermal Processing of Food, Washington State
University, Pullman, USA
A. Lopez-Gomez (&)
Departamento de Ingenierıa de Alimentos y del Equipamiento
Agrıcola, Universidad Politecnica de Cartagena, Paseo Alfonso
XIII, 48 30203 Cartagena, Spain
e-mail: [email protected]
123
Food Eng Rev (2009) 1:84–104
DOI 10.1007/s12393-009-9005-5
Nevertheless, the incidence of foodborne diseases is
rising in developing countries, as well as in the developed
world [158]. For example, in UK while cases of Cam-
pylobacter and Salmonella have fallen (due to regulation,
training, and public information campaigns), E. coli and
Listeria are on the upswing; the number of Listeria cases
has almost doubled since 2000, a troubling indication that
more work needs to be done in combating these pathogens
[60].
There has been an increased demand for fresh and
minimally processed fruits and vegetables mainly because
of the health benefits associated with their consumption,
but foodborne illnesses associated with consumption of
these produces has also increased in the last two decades.
In fact, the proportion of foodborne disease outbreaks
associated with these fruit and vegetable products doubled
from 1988 to 1991 [111]. Also, concerning muscle-based
foods, given the significant market trends toward fully
cooked and ready-to-eat food products, there is a growing
technical need for ensuring food safety from the start of
processing to distribution to the consumer [115].
Food Safety Engineering: An Emerging Specialization
and Research Field
Food safety is therefore an important concern in food
engineering. In fact, the safety of the entire food supply
chain depends on food engineering innovations and designs
that apply the latest technologies to real-world problems in
production and processing [11, 108, 115, 153].
After CFSE in 2007 it was clear that engineering should
be an integral component of food safety research. Engi-
neering is necessary in the development of physical and
chemical mechanisms and devices for detection of micro-
bial and chemical hazards in the food supply. In fact, if we
define engineering as the hardware that makes it possible
to carry out a technology (using software or ‘‘know how’’),
food safety engineering could be considered as a type of
food engineering hardware (e.g., the physical solutions for
processing; packaging, and storage equipment; facilities—
including control systems; rooms in food factory; other
facilities used in food supply chain) that could be used to
achieve the required levels of food safety and security in
the food supply chain [156]. Marks [115] stated that while
epidemiologists, food microbiologists, and chemists
advance the understanding of foodborne microorganisms
(e.g., explaining how microorganisms cause diseases, react
to environmental influences, and can be isolated and
identified), this knowledge must ultimately be scaled-up by
food engineers to design and implement technical solutions
to the real problems facing the food industry (Fig. 1).
Food safety engineering is an emerging specialization
that involves the application of engineering principles to
address microbial and chemical safety challenges [7].
According to Ramaswamy et al. [153], food safety engi-
neering study must include: (i) intervention technologies
(traditional and novel nonthermal intervention technologies,
chemical interventions, and hurdle approach), (ii) control/
monitoring/identification techniques (biosensors), (iii)
packaging applications in food safety (active packaging;
intelligent or smart packaging; tamper evident packaging),
and (iv) tracking and traceability systems. At Cornell Uni-
versity a graduate training program offered in Food Safety
Engineering [130] included: (i) novel processing methods
for food pathogen inactivation, (ii) modeling of microbial
inactivation kinetics, (iii) development of antimicrobial
techniques, and (iv) development of novel microbial
detection methods.
At Pennsylvania State University, a Food Safety Engi-
neering course introduces diverse topics in microbial food
safety from an engineering perspective, including: plant
layout, construction materials, equipment design, predic-
tive microbiology and modeling, conventional and novel
detection and enumeration methods, conventional and
novel processing methods, emergency contingency plans,
and current responsibilities and regulations of federal
agencies for food safety [152].
Another important reference to food safety engineering
is the Center for Food Safety Engineering at Purdue Uni-
versity, originally a ‘‘food safety engineering project’’
involving a 5-year cooperative agreement with USDA-
ARS to develop better methods of detection and prevention
of biological and chemical foodborne contaminants.
Today, the mission of this Center is to develop new
knowledge, technologies, and systems for detection, and
prevention of chemical and microbial contamination of
foods, with a multi-disciplinary approach, including a
strong engineering component [34].
Fig. 1 Bulk storage aseptic tanks
Food Eng Rev (2009) 1:84–104 85
123
As stated earlier, this article demonstrates the need for
the food safety engineering perspective. This perspective is
needed in order to produce high quality food products
(minimally processed) that are both safe and secure, and
involves a multi-disciplinary approach. The main compo-
nents of this engineering are: (i) predictive microbiology as
a tool to evaluate and improve food safety in traditional
and new processing technologies, (ii) advanced food con-
taminants detection methods, (iii) advanced processing
technologies and food safety, (iv) advanced systems for
food re-contamination control, and (v) advanced systems
for active and intelligent packaging.
Predictive Microbiology
Predictive Mathematical and Probabilistic Models
Predictive microbiology is based upon the premise that the
responses of microorganisms to environmental factors are
reproducible, and that it is possible, taking into account past
observations, to predict the responses of microorganisms in
particular environments [168]. One of the main objectives
in this area is to build, estimate, assess, and validate
mathematical or probabilistic models with which it is pos-
sible to describe the behavior (growth or inactivation) of
foodborne microbes in specific environmental conditions
(e.g., NaCl, pH, aw, or temperature). In this regard it is
important to predict the possibilities for growth of micro-
organisms, as affected by different factors, and for the
survival of a microbial population exposed to a preservative
treatment. These microbial responses are summarized in the
form of predictive models, which quantify the effects of
interactions between two or more factors, and by interpo-
lation, can be used to predict responses to conditions that
have not been tested explicitly [105, 196].
Predictive microbiology is gaining interest as a tool to
guarantee the production of safe foodstuffs, and it has also
been recognized as a versatile and helpful tool for risk
assessment [125]. Mathematical and probabilistic models
are very useful for not only hazard analysis and critical
control points, but also for making decisions in scenarios
where there is uncertainty. The successful application of
predictive microbiology depends on the development and
validation of appropriate models [122]. Many manufactur-
ers have used predictive microbiology to reduce consumer
risk associated with pathogen growth, and even to prevent
the growth of spoilage microorganisms [125].
In the last 20 years several new nonthermal technologies
have been developed (high intensity pulsed electric fields,
high hydrostatic pressure, pulsed light, etc.), and some have
been applied successfully to the food industry [9]. When
used for food preservation, some prior information must
first be known. For example, regarding food safety, it is
important to know the mechanism by which the new tech-
nology inactivates microorganisms, which microorganisms
are being inactivated, whether these microorganisms can
develop resistance or cross resistance (and to which level),
as well as the effect of physical and/or chemical factors on
its effectiveness and to which point these effects can be
predicted. Here is where predictive microbiology has a new
field of application.
In this regard, many predictive models for heat inactiva-
tion assume a logarithmic linear relationship between the
number of microorganism survivors and time after heat
treatment, having in common their use of D or k parameters
as kinetic rates. In such models, a deterministic nature of the
microbial inactivation is assumed, each microorganism
having the same probability of dying and death being due to
one single event. Nevertheless, in most cases, this assump-
tion is not valid because of the presence of shoulders and tails
in the survival curve [32]. Figure 2 shows the survival curve
of Candida lusitaniae CECT 12006 at 52.5�C in tomato
juice. This survival curve is clearly not linear, and when a D
value is calculated from the slope of the regression line
(dashed line), a significant difference between the observed
and the expected counts is obtained. The longer the time of
exposure, the higher the miscalculation made. Moreover, it
has been showed many times that when microorganisms are
exposed to the new nonthermal technologies (almost all),
inactivation does not follow first-order inactivation kinetic.
In this context, classical deterministic models, based on first-
order kinetics, can no longer be used.
Hence, lately, some authors have considered the survival
curve as the cumulative form of lethality event distribution
[45, 68, 84, 110, 144], considering the death of each
microorganism as a probabilistic case. In these probabilistic
models, it is assumed that each microorganism of the pop-
ulation has a different sensitivity to an inactivating agent
2
3
4
5
0 2 4 6 8 10 12 14 16 18 20Time (min)
log
N
Fig. 2 Survival curve of Candida lusitaniae CECT 12006 at 52.5�C
in tomato juice, fitted using linear regression (dashed line) and the
Weibull distribution function (full line)
86 Food Eng Rev (2009) 1:84–104
123
and dies at a specific time. Hence, the inactivation time is
different for each microorganism and the form of the sur-
vival curve depends on the resistance distribution of the
microbial population. One stochastic alternative that has
been recently used by different authors to describe nonlinear
survival curves is based on the Weibull distribution function
[68, 110, 144, 189]. The Weibull distribution has been
applied successfully for modeling inactivation kinetics of
microorganisms exposed to lethal agents, such as natural
antimicrobials for food protection, high pressures, electric
pulses, or chlorine [55–57, 147–149, 193]. Even Hassani
et al. [81] used the Weibull distribution to describe thermal
inactivation of vegetative cells (Staphylococcus aureus,
Listeria monocytogenes, Enterobacter faecium, E. coli, and
Salmonella spp.) under non-isothermal conditions. In the
survival curve depicted in Fig. 2, the regression line cor-
responding to the survival function of the Weibull distri-
bution function (full line) shows a much better fitting to the
observed values than the first-order kinetics regression line
(dashed line).
Microbial system biology is also gaining interest and it
is being incorporated into predictive microbiology [123]. In
this regard, empirical models, which consider microor-
ganisms as ‘‘black boxes’’ with no a priori knowledge
about them, are being exchanged for grey or even white
box models, in which modeling is more and more a
mechanistic basis and thus the description of well-charac-
terized microbial responses to environmental factors also
has a physiological meaning [23]. Thereby, the foundation
of models is significantly reinforced and their robustness
increases. As stated at the second research summit of the
Institute of Food Technologists, held in Orlando January
2003, ‘‘the paramount purpose of microbial inactivation
data and calculations deriving from whatever model is to
be applied in development of a calculated process that is
safe, robust in its design, and flexible in approach such that
deviations can be evaluated for safety impact.’’
Databases and Computer Programs
The former predictive models can be attributed to Esty and
Meyer [64], who found that the inactivation kinetics of
Clostridium botulinum spores exposed to wet heat followed
an exponential decay. Monod [129] successfully applied a
kinetic exponential model to describe the growth of fer-
mentative microorganisms. But the greatest advance in
predictive microbiology took place in the 1980s, as linked
to the development of powerful computers.
The huge amount of data generated in recent years to
predict the behavior of microorganisms under different
environmental conditions has allowed for the development
of mathematical models, which have enabled scientists to
predict the behavior of microorganisms under certain
conditions, including large databases and computer pro-
grams, which facilitate its usage. These data sets are
available for food microbiologists, manufacturers, risk
assessors, and legislative officers. Some of these programs
are free while others are commercial and need to be reg-
istered before use. The first free model package, the
Pathogen Modeling Program [187], was created by the
Eastern Regional Research Center of the United States
Department of Agriculture. This predictive microbiology
application was designed as a research and an instructional
tool for estimating the effects of multiple variables on the
growth, inactivation, or survival of foodborne pathogens.
The first validated, commercialized predictive package, the
Food MicroModel [6], was built upon data collected after a
coordinated research program initiated and funded by the
British Ministry of Agriculture, Fisheries, and Food in
1988, and offers the advantage that it has been validated in
foods; this software package predicts the growth, survival,
and thermal death of major food pathogens and food-
spoilage organisms in a wide range of foods. These two
independent data sets constitute thousands of microbial
growth and survival curves that are the basis for numerous
microbial models used by the industry, academia, and
government regulatory agencies.
In 2003, these two data sets were unified in a common
database and are now publicly and freely available; the
database, known as ComBase [181], follows a structure
developed by the Institute of Food Research (IFR) of the
United Kingdom. Many European research institutions
have also added their data to ComBase, and data have also
been compiled from scientific literature at IFR. In 2006, the
Australian Food Safety Center of Excellence also joined
the ComBase Consortium [8]. At present, ComBase con-
tains up to 40,000 records containing full bacterial growth
and survival curves.
In predictive models of ComBase, factors such as pH,
NaCl or aw can be entered as independent variables to
obtain the variation in the dependant variable, usually the
inactivation or growth kinetic parameter. The system has
become a vital tool to assure the safety of foods in inter-
national trade. The use of ComBase avoids unnecessary
repetition of experiments, increases the efficiency of
research efforts, standardizes the data sources for microbial
risk assessors, and helps to improve food safety and qual-
ity. Nevertheless, many of these models have been built
with focus on the inactivation of microorganisms exposed
to heat or on the growth under usual storage conditions.
Advanced Food Contaminants Detection Methods
Biosensors are devices that can combine a biological/bio-
chemical element with a physical signal that can be
Food Eng Rev (2009) 1:84–104 87
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translated into an indication of the safety or quality of the
food. There are several types of biosensors, including
biological, electrochemical, etc. Biosensors can measure
parameters that are related to a hazard (e.g., temperature
during storage of a food product) or in the presence or
concentration of a hazard (toxin, pathogenic microorgan-
ism, or indicator microorganism). They contribute signifi-
cantly to food product safety and are valuable tools
for controlling processes in food manufacturing and
packaging. Biosensors are particularly relevant for novel
foods and/or technologies.
Rapid Detection Tools
The rapid detection of foodborne microorganisms or tox-
ins, or alternatively, indicator microorganisms, is one of the
main tools used to ensure food safety and quality along the
food chain. Since food safety and quality are also deman-
ded by consumers, efficient analytical methodologies are
needed in the food industry to ensure this quality. Classical
microbiological methods for the presence of microorgan-
ism in foods involve several steps and final confirmation by
biochemical and/or serological identification. This makes it
very time consuming and sometimes not sufficiently reli-
able. Molecular techniques have become an alternative
since they can give results in short time intervals, they are
specific and have a potential for automation [165].
Polymerase chain reaction (PCR) has become the more
extensively used molecular technique [89]. As a molecular
diagnostic tool, it has the potential to significantly reduce the
time necessary for detection and screening of foods with
technologies that offer real-time, finger-printing, quantita-
tive, RNA-based or a combination of virulence gene
expression assessment methods [117]. However, the food
industry has been slow to adopt the technique as a rapid
method, probably due to the lack of a universal DNA
extraction procedure, as the composition of the food medium
affects its sensitivity [119, 166]. Real-time PCR, which
measures reaction progress during each amplification, can
require less than 30 min for amplification and data analysis
[186]. There are real-time chemistries available for use in
PCR and they can be divided into not sequence-specific and
sequence-specific ones [117].
RNA-based methods can be used as an alternative to
DNA ones, since differentiation of living from dead bac-
teria can be difficult because DNA is persistent in dead
cells. It can be very effective also for viable, but not cul-
turable microorganisms, as well as to assess virulence gene
expression. The mRNA is ideal to use as an indicator of
metabolic status of bacteria or presence of viable, non-
culturable pathogens, since it is not persistent after cell
death [118].
Genomics is expected to play a major role in food
microbiology guiding the behavior of spoilage and patho-
genic microorganisms upon and after processing. The
analyses will provide a molecular finger-print, a molecular
mechanistic basis, of the survival strategies of microor-
ganisms of concerns in various foods [22]. DNA micro-
arrays offer the opportunity for rapid detection and
enumeration of many different bacterial species. An array
is an orderly arrangement of nucleic acid samples and
provides a medium for matching known and unknown
DNA samples on the basis of base-pairing rules and for
automating the process of identifying the unknown.
Microbial detection arrays have so far been designed on the
basis of phylogenetic relationships (e.g., 16S rRNA), whole
genomes, and specific functional–gene-traits [113]. DNA
microarray technology is implemented in two formats
[117]: identification of the DNA sequence and determina-
tion of the expression level of genes. It offers huge possi-
bilities, such as screening of ingredients using DNA-chip-
based techniques identifying molecular markers that will in
the future allow the identification of the occurrence of food
related bacteria and prediction of their preservation stress
resistance [22].
Optical biosensors have the potential for rapid and
sensitive detection of foodborne pathogens. They are non-
destructive, cost is low, and can detect and identify bacteria
or even colonies grown on agar plates in real time. Optical
light scattering methods include spectroscopy, flow
cytometry, and surface plasmon resonance. These methods
are suitable in microbial detection in food, clinical speci-
mens, and environmental samples [16] and provide a
simple approach with a minimum number of steps; they are
both non-destructive and rapid and can be implemented for
use online during product manufacturing.
New alternatives are being developed that may become
useful in the food industry over the next years, such as fiber
optic biosensors, which utilize the total internal reflection
property of light while traveling through the waveguide,
generating a boundary of evanescent waves on the surface
of the waveguide [101]; another alternative is Fourier-
transform infrared spectroscopy [25, 107].
Parameter Integrators
The devices used to integrate the temperature changes
along time (e.g., during distribution of a chilled food) are
frequently described as time–temperature integrators
(TTIs). In general, these small devices show irreversible
changes in relevant characteristics related to food, (e.g.,
quality, microbial load), but by means of an easily mea-
surable (in an exact and precise way) parameter, as in
temperature, that mimics changes produced in a sensitive
target (e.g., quality, microorganisms, enzymes, etc.) of the
88 Food Eng Rev (2009) 1:84–104
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food. They are contained in the foodstuff suffering the
same treatment at variable conditions [116]. According to
the sensor element, parameter integrators can be classified
in different groups as:
– Chemical TTIs: Based on detection of chemical reac-
tions to quantify the impact of the process. Different
chemical systems, such as thiamine heat inactivation
and color changes produced by sugar and amino group
reduction, have been used [65, 85].
– Physical TTIs: Based on diffusion phenomena, i.e., the
diffusion of colored chemical substances as a function
of existing conditions (time, temperature) [199] or on
the ionic diffusion and capacity of a semiconductor
metal [179].
– Biological TTIs: Based on proteins (enzymatic or
immunochemical) or microbiological types. In enzy-
matic TTIs, the residual activity is directly related to
temperature. Bacillus licheniformis amylase [53],
galactosidase, lipase, and nitrate reductase have been
used [116]. Immunochemical methods are based on the
antigen–antibody reaction. In heat-treated products
proteins can be affected and binding sites changed,
affecting antigenic capacity loss [21]. Although these
systems provide quick detection measures, they can be
inactivated at high temperatures and are not suitable for
products heated in HTST range.
Microbiological TTIs are the most reliable alternative
used to control the efficiency of sterilization processes in
the food industry. They consist of a carrier system inocu-
lated with a microorganism of well-known growth and/or
inactivation parameters. The selection of microorganisms
as biological indicators depends on the specific applica-
tions for which they are designed [150]. Microbiological
control systems can be divided as follows: qualitative
systems, to indicate if microorganisms have been exposed
or not to established critical conditions; and quantitative
systems, to estimate the count increase or reduction, as
related to conditions to which the product has been directly
exposed.
From a food safety evaluation point of view, thermal
process design should be evaluated based on the heat
impact in the coldest spot inside the food. TTIs can be used
as wireless instruments to follow and identify slow-heating
points inside containers or aseptic packaging systems when
other systems are not adequate [116]. They can also be of
great value for novel processes based on the application of
heat or in nonthermal technologies. However, it is impor-
tant to consider that the target sensor element could be
different from those established for heating or mild pres-
ervation techniques.
On the other hand, the GoodFood project was recently
carried out using micro- and nano-technology to develop
portable devices that could detect toxins, pathogens, and
chemicals in foodstuffs on the spot. In this scenario, food
samples would no longer have to be sent to a laboratory for
tests but could be analyzed for safety at the farm, during
transport and storage, at processing and packaging centers,
or even in the supermarket [28]. Researchers at Cornell
University in the U.S. have developed new devices called
nanoscale resonators that may enable faster, easier, and
more reliable testing for mad cow disease [100]. The new
devices can detect the abnormally structured proteins
called prions, which are known to cause mad cow disease,
as well as other neurodegenerative diseases such as scrapie
in sheep and Creutzfeldt-Jakob disease in humans.
According to this work, the vibrational resonant frequency
of the new devices changes when prions bind to the reso-
nator’s silicon sensor.
Nanoscience and nanotechnology can be defined as the
understanding and manipulation of materials at the atomic,
molecular, and macromolecular scales. The applications of
nano-based technology in the food industry may include
nanoparticulate delivery systems (e.g., micelles, liposomes,
nanoemulsion, biopolymeric nanoparticles, and cubo-
somes), food safety and biosecurity (e.g., nanosensors), and
nanotoxicity. Nevertheless, nanotechnology has already
provoked public concern and debate. Nanomaterials (e.g.,
carbon nanotube, silver, silica, titanium dioxide, and zinc
oxide) exhibit properties not found at the macro-scale and
might result in unpredictable safety problems and risks
[37].
Advanced Processing Technologies and Food Safety
Increasing consumer demand for ‘‘fresh-like’’ foods has led
to much research effort in the last 25 years in the devel-
opment of new mild methods for food preservation.
Microorganisms are the main agents responsible for food
spoilage and food poisoning and therefore food preserva-
tion procedures are targeted towards them. Thermal treat-
ment is the most widely used procedure for microbial
inactivation in foods. Thermal treatments generally, how-
ever, cause undesirable changes in food flavor, color, tex-
ture, and nutritional attributes such as protein and vitamin
destruction.
On the other hand, nonthermal processing/preservation
methods are of interest to food scientists, manufacturers
and consumers because of the minimal impact these
methods have on the nutritional and sensory properties of
foods [2], including on shelf-life extension in the inacti-
vation of microorganisms at sublethal temperatures [112].
Nonthermal food processing methods are also considered
more energy efficient and environmentally friendly than
conventional thermal-based treatments [182]. Together
Food Eng Rev (2009) 1:84–104 89
123
these reasons have promoted the development of nonther-
mal processing methods for microbial inactivation, among
which ultra-high pressure, ionizing irradiation, pulsed
electric fields, pulsed light, ultrasound, magnetic fields, and
dense phase carbon dioxide are attracting much interest.
However, the high resistance of certain enzymes and
microorganisms to nonthermal processes, especially bac-
terial spores, limit their application. To expand their use in
the food industry, combinations of nonthermal technolo-
gies with traditional or emerging food preservation tech-
niques are being studied (as hurdle technologies), and
could present a number of potential benefits to food pres-
ervation [154].
High Hydrostatic Processing (HHP)
High hydrostatic pressure (HHP) and ultra-high pressure
are both the names for the same process. HHP is a cold
pasteurization method that involves the application of
pressures ranging from 100 to 1000 MPa. It inactivates
vegetative microbial cells by breaking non-covalent bonds
and causing damage to the cell membrane. High hydro-
static pressure disrupts secondary and tertiary structures of
macro-molecules, such as proteins and polysaccharides,
and alters their structural and functional integrity in a
pressure-dependent way [114].
HHP often yields better results when combined with
thermal processes. Clostridium botulinum cells, but not
their spores, can be destroyed at temperatures 90–110�C
and pressures 500–700 MPa. Research has been done to
increase this pressure to 800 MPa in combination with low
or high temperature to potentially achieve ambient tem-
perature/microbiological shelf stability [18]. HHP use
cannot, for example, deliver low acid foods that are
ambient temperature shelf stable [39].
The most widely used commercial applications of HHP
are for products such as refrigerated guacamole, salsas,
entrees, and delicatessen meats, which are all processed in
packages. This technology can also be used for nonthermal
processing of avocado halves, applesauce, cured ham, and
chopped onions. It is further employed to pasteurize oys-
ters while maintaining a raw designation. HHP can be
used as a post-packaging lethality step for the inactivation
of Listeria monocytogenes as well on ready-to-eat meats
such as sliced ham and deli meat. The integration of high
pressure with other developed processing operations, such
as blanching, dehydration, rehydration, frying, freezing/
thawing, and solid–liquid extraction has been shown to
open up new processing options [157]. Overall, HHP has
demonstrated sufficient benefits with minimal alterations
to the product, leading to the conclusion HHP could
become a more significant food preservation force in the
future [131].
Ionizing Radiation (IR)
Food irradiation by IR is a nonthermal food pasteurization
process that involves the application of electromagnetic
waves or accelerated electron beams to food. Radiation
sources can be gamma rays from cobalt-60, electron
beams, or X-rays; the amount of irradiation absorbed by a
food is measured in kilogray (kGy). It has been found that
at low doses, irradiation has little effect on food’s nutri-
tional and organoleptic qualities. For all irradiation pro-
cesses in the USA approval must be obtained from the
Food and Drug Administration (FDA) because such pro-
cesses are defined as a food additive. More than 40 coun-
tries have approved irradiation for over 100 food items.
Further, the World Health Organization has declared that
irradiation of any food commodity up to 10 kGy is not
a toxicological hazard.
IR reduces or eliminates spoilage and pathogenic
microorganisms, such as Salmonella, E. coli O157:H7,
L. monocytogenes, and Campylobacter jejuni by frag-
menting DNA. Accelerated electron beam application also
has potential use, either alone or followed by heat treat-
ment to preserve the food [54]. Irradiation processes min-
imize post-harvest loss and inhibit sprout formation in
products such as potatoes. Not all foods, however, are
suitable for irradiation processes. Milk and other protein
foods can develop problems with off-flavor, odor and color,
and some fruits may exhibit softening and discoloration,
especially at higher dose levels.
Post-packaging potential for irradiation includes the
disinfection of grains, legumes, spices, fruits (e.g., melons),
vegetables (e.g., lettuce), and tubers; color retention in
fresh meats; and microbiological control in eggs, poultry,
pork, and other meats. In the production of raw, non-heated
or non-processed foodstuffs, irradiation may also be used
as a critical control point [80].
Pulsed Electric Fields (PEF)
PEF technology involves the application of short duration
(1–100 ls), high electric field pulses (10–50 kV cm-1).
Although PEF is a nonthermal process, an increase in
temperature occurs in the processing chamber. This process
attains a 5 log-reduction of most pathogenic bacteria by
rupturing the cell membranes in liquid media. It causes
only minimal detrimental changes to the physical and
sensory properties of foods [2], helps retain food’s ‘‘fresh’’
quality, and assists in nutrient retention.
PEF can be applied to the pasteurization of liquid
products in continuous systems, such as milk [169], yogurt,
juices, liquid eggs [170], soups, brines, and other products
that can withstand high electric fields. PEF has limited
effects on microbial spores [135], cannot be used on
90 Food Eng Rev (2009) 1:84–104
123
products that contain or could form air bubbles, and cannot
be used on foods having higher or variable electrical con-
ductivity. PEF has mainly been applied to improve the
quality of foods [66] and a lot of research is ongoing today.
Pulsed Light (PL)
Pulsed visible light involves fleeting, but intense, pulses of
broad spectrum light; PL can inactivate many microor-
ganisms in just a few flashes, and within a fraction of a
second. The antimicrobial effects of these wave lengths are
primarily mediated through absorption by highly conju-
gated carbon-to-carbon double bound systems in proteins
and nucleic acids [67]. For most applications, a few pulsed
light flashes within a fraction of a second will yield high
levels of microbial inactivation.
PL can only be used on product surfaces. Foods on
which PL may be applied include baked goods for mold
inactivation, and shrimp and fish for chilled shelf-life
extension. Other products that may benefit from PL include
chicken wings, hot dogs, eggs, and cottage cheese. Pulsed
high-intensity light has shown some promise in treating
package material and microbiological destruction in
products.
Ultrasound
Ultrasound is defined as sound waves with frequencies
above the threshold for human hearing ([16 kHz). Ultra-
sound utilizes at least 20,000 vibrations per second to
achieve a bactericidal effect in microorganisms and causes
enzyme inactivation by cell lysis.
Ultrasound is one of the simplest and most versatile
methods used for cellular disruption and food extract pro-
duction [44, 192]. This technology works best when used in
conjunction with heat and pressure [86, 155], but it can be
used alone for fruit juices, sauces, purees, and dairy
products. Foods with particulates and other interfering
substances do not react well to ultrasound. Ultrasound has
not yet demonstrated nor achieved any major beneficial
effects that warrant serious consideration for processing or
packaging.
New Technologies and Food Safety
Alternative food processing and preservation technologies
attract special interest in the food industry because of the
growing consumer demand for foods not only safe, but for
products that retain the characteristics of fresh or freshly
prepared foods. Such foods are being developed to a large
extent in reaction to consumers. Requirements for foods
more natural and therefore less heavily preserved (e.g., less
acid, salt, sugar) and processed (e.g., mildly heated), less
reliant on additive preservatives (e.g., sulfite, nitrite, ben-
zoate, sorbate), fresher (e.g., chill-stored), and more con-
venient to use (e.g., easier to store and prepare) than
previously [79] have led to the development of mild
preservation technologies, which are gaining more and
more importance with time. Examples include the afore-
mentioned high-pressure processing, pulsed electric fields,
light technologies, cold plasma, and use of biopreserva-
tives. Mild preservation technologies enhance the shelf life
of foods; they are usually applied at room temperature and
have a minor impact on the quality and fresh appearance of
food products. They are referred to as mild, since they
impose little stress on foods. This, on the other hand,
increases the importance of food safety considerations. An
extended shelf life and a ‘‘fresh-like’’ product presentation
emphasize the need that food safety risks should be taken
into account, along with possible health benefits to con-
sumers. The introduction of novel preservation methods
has stimulated research in microbiology, technology, and
food processing. The adoption of mild preservation tech-
nologies under European legislation is an ongoing process,
as shown by the Novel Food Regulation [160].
Compared to a decade ago, research on mild preserva-
tion technologies has made a tremendous step forward. At
this moment, novel technologies, such as high pressure,
pulsed electric fields, and use of biopreservatives are
beyond the first development phase. Equipment is available
on different scales and several process conditions have
been described. Possibilities for using these technologies in
preservation of food products are being reported and the
effects on product quality have become more widely
known. Currently, some products are on the market (e.g.,
high pressure processed) or will be on the market in the
near future (e.g., pulsed electric fields treated) [141].
There are some major trends in the research on novel
preservation technologies. The first trend is related to
understanding the effects of novel preservation technolo-
gies on microorganisms. As these technologies are cur-
rently used, or will be used in the near future for producing
food products, focus on the mechanisms of inactivation of
microorganisms becomes crucial. Not only is the amount of
inactivation by a certain technology important, but also the
aspects such as sublethal inactivation, differences between
strains and between subpopulations, and stress adaptation.
Survival of microorganisms exposed to the stress of pres-
ervation technology can be the result of three main sys-
tems. Firstly, the resistance is induced and the survival is a
cause of intrinsic properties. Secondly, the resistance is
genetically acquired through mutation and selection. For
instance, damage to cell membranes, enzymes, or DNA is
the most commonly cited cause of death of microorganisms
by emerging preservation technologies. The effect of those
technologies has a range of consequences on individual
Food Eng Rev (2009) 1:84–104 91
123
cells within a population of microorganisms; some bacteria
are killed, others survive, and a proportion of the surviving
population is damaged or injured [47]. The latter is the
population of concern because the damage may be repaired
and during the reparation stage the bacteria may acquire
new or modified characteristics [104]. Several bacterial
species are naturally transformable and become trans-
formable in the natural course of their life cycle, while
others become transformable under certain conditions [50],
such as when the bacterial cell-membrane integrity is
compromised as a consequence of the treatment process;
then the acquisition of resistance is due to the uptake of
extra-chromosomal DNA, which has been acquired from
other bacteria [138]. In food processing, DNA released
from lysed bacterial cells is vulnerable to physical degra-
dation, e.g., by heat, shearing forces and chemical degra-
dation, as shown in fruit juice [194] and in a variety of
different food products (reviewed by [190]). The protective
action against DNAases of individual food components
such as arginine, polyamines, and biogenic amines is
shown by in vitro experiments [190]; the protective action
of the complex food matrix in sausages is reported by
Straub et al. [178]. Competence (the ability to take up DNA
from their environment) of bacterial species such as E. coli
can be induced by chemical or physical conditions, such
as presence of salts, temperature shifts, electro-shocks
[30, 31, 50]. The development of competence and natural
transformation has been shown for Bacillus subtilis in milk
[99, 202]. Efficiency of bacterial transformation is strongly
enhanced by the concentration of DNA in the close vicinity
of the bacterial cell and under high nutrient conditions, as
may occur in biofilms [12]. Biofilms are commonly present
in the food processing environment [5, 200] and synergistic
effects between biofilm formation and plasmid transfer
have been observed [161]. In addition, sublethal food
preservation stresses (e.g., high/low temperature, osmotic
and pH stress) can increase the horizontal transmission of
plasmid DNA to bacterial cells [120]. Rodrigo et al. [163]
observed transformation in E. coli cells after a treatment
with pulsed electric fields and found that the transformed
cells acquired a rifampicin-resistant plasmid. Nevertheless,
the range of compatibility between the free DNA and the
intact recipient bacteria is often narrow [121].
Regarding the implementation of novel preservation
technologies, special attention paid to food safety issues
regarding these technologies is needed. Issues are not only
related to microbiology but also aspects such as toxicology,
for example possible toxicity due to metal release as a
result of electrode degradation during pulse electric fields
treatment, should be considered. Designed and engineered
pulsed electrical field systems resulting in metal release of
less than 0.5 lg/kg product should be a very important
goal. Further, processing conditions of novel technologies
are chosen accordingly, so that safe foods are produced
without the use of extreme conditions that could result in
unwanted negative effects regarding quality. Thus, an
important topic is the need for hygienic and ultra-clean
processing and packaging since the use of mild preserva-
tion technologies mostly results in pasteurized products,
which have to be stored at low temperatures until con-
sumption (Fig. 3).
The legislation of novel food technologies was incor-
porated into the Novel Food Regulation [160], and
includes new production processes. These processes were
not used on a significant scale before introduction to the
Novel Food Regulation and resulted in significant differ-
ences in the composition or structure of food products.
Central in this regulation is the concept of substantial
equivalence. If a new process results in products, which
are not substantially equivalent with common products,
the Novel Food Regulation has to evaluate the process
on safety issues, such as microbiology, toxicology, and
allergy concerns.
Mild preservation technologies have in common that
they are often limited in the type and number of micro-
organisms killed. For example, pulsed electrical field
treatment does not inactivate bacterial spores, and high
pressure inactivates spores only if applied at elevated
temperatures. The implementation of mild preservation
technologies requires special attention to the quality of raw
materials, optimization of process conditions, hygiene of
process lines, high quality packaging (pack integrity,
packing under modified atmosphere), and specific storage
conditions. Good hygienic design is essential to prevent the
contamination of minimal processed products with sub-
stances that would adversely affect shelf life or the
health of the consumer. This contamination might be
Fig. 3 Ultra-clean packaging facility for fruit juices
92 Food Eng Rev (2009) 1:84–104
123
microbial (e.g., pathogens), chemical (e.g., lubricating
fluids, cleaning chemicals), and physical (e.g., glass).
Processing skills are essential, especially hygienic engi-
neering of the equipment. Basic hygienic design require-
ments include the construction material, surface finish,
joints, fasteners, drainage, internal angles and corners, dead
spaces, bearings and shaft seals, instrumentation, doors,
covers and panels, and controls [106].
In this context, Food Safety Authorities can play an
important role in assessing the safety of the new technol-
ogies applied in the food industry. Recently, the European
Commission has requested an initial scientific opinion from
EFSA relating to the risks arising from nanoscience and
nanotechnologies on food and feed safety and the envi-
ronment. The request also asks to identify the nature of the
possible hazards associated with actual and foreseen
applications in the food and feed area, and to provide
general guidance on data needed for the risk assessment of
such nanotechnologies and applications. In this case,
EFSA’s mission is: (i) revision of scientific advice and
scientific and technical support in all fields that have a
direct or indirect impact on food and feed safety, to provide
to the European Commission, Parliament, and Member
States independent information on all matters within these
fields, and (ii) risk communication within its remit net-
working and collaboration with Member States. Other
opinions have been prepared in response to questions raised
from the Commission in relation to the use of different
technologies for preservation and food preparation. Those
opinions can be downloaded from http://www.efsa.eu.
int/EFSA/efsa_locale-1178620753812_ScientificOpinion
PublicationReport.htm.
Advanced Systems for Food Re-Contamination Control
Barriers Technology for Food Safety and Security
Early on, the main concern of food security was that the
rights of people to have a steady diet be assured. Later,
food security referred to measures that could be taken to
obtain healthy food that was beneficial and not harmful to
health, and food not contaminated accidentally. In 2001,
the concept of food security also extended to all measures
designed to prevent the occurrence of intentional contam-
ination of food harmful to people’s health. NFPA [139],
after the terrorist attacks of September 11th, elaborated a
Food Security Manual, for processors, distributors and
retailers, including a security checklist with the objective
of providing companies with a document to facilitate self-
assessment of food security measures by identifying a wide
range of factors that should be considered (independent of
specific processing steps). The focus of this document is
distinct from GMPs and HACCP, and is on the prevention
of intentional product contamination.
Safety and security are a concern in virtually all engi-
neering processes and systems. In engineering practices,
there are many principles and methods recommended for
the engineer as a means to ensure safety. Moller and
Hansson [128] state that safety considerations can be
divided into three different types: (i) adherence to good
practice, (ii) safety analysis, and (iii) inherently safe
design. A recommended first step in safety engineering is
to minimize the inherent dangers in the process as far as
possible. This means that potential hazards are excluded
rather than just enclosed or otherwise coped with. Also, the
concept of fail-safe is in practice mainly used for specific
methods and principles for keeping the system safe in case
of failure, such as shutting down the components or the
entire system. An application of the fail-safe principle is
the usage of several safety barriers [128]. The NFPA [139]
document considers a kind of barriers technology, as
applied to protect the food product from intentional con-
tamination but that is equally valid to protect it from
accidental contamination.
The first barrier refers to outside premises, as the
fencing or other barriers, to prevent unauthorized access
within the boundaries of the facility (monitoring and
controlling these areas, with access control to transport
vehicles, personnel, and domestic and non domestic ani-
mals). The basic idea is that the first barrier must be
normally closed, with a unique access (a door or several
doors) for entry personnel and transport vehicles with raw
matters and end products. The second barrier concerns the
inside premises, involving the closing of the buildings of
the food factory, which must be closed in a normal manner
(windows and doors). All entrances/exits must be con-
trolled, in the same building and between buildings, as
well as connections to other areas through openings for
vents, air circulation lines, pipes, electrical lines, drains,
etc. In this way, the entrance of insects, rodents, and
personnel is controlled within the processing and pack-
aging rooms (through doors, windows, floor drains, and
ceilings). The third barrier is the segregation of restricted
areas (zones) within the plant, which have different
hygienic requirements and controlled access [191]. The
fourth barrier involves the clothes worn to protect the
product from human contamination, mainly in the clean
room areas dedicated to ultra-clean and aseptic processing
and packaging [24] (Figs. 4 and 5). The fifth barrier is the
processing equipment (including storage and conveying
systems), which must have an adequate hygienic design
and must be closed normally to protect the food product
from external contamination [92, 108]. The food safety
engineering must solve the detail engineering (drawings
and specifications) to implement each one of these barriers
Food Eng Rev (2009) 1:84–104 93
123
to protect the food product from intentional and accidental
contamination.
Hygienic Design in the Food Factory
As cleaning in place (CIP) procedures are used throughout
the food industry as the only practical way to clean closed
process equipment [72], some design details are reported as
being hygienically risky because of the undesired fluid
flows, such as those found in up-stands, dead-ends, heat
exchangers, expansions or contractions, etc. [58, 82]. So, to
produce safe and wholesome foods the food safety engineer
should check carefully the hygienic design, installation,
handling and maintenance of production or the processing
‘‘hardware’’ [92].
Food engineering provides a number of rules and
knowledge to design and run food processing plants.
Substantial knowledge is available with respect to equip-
ment design, plant design (stressing all aspects of civil
engineering such as walls, floors, heating, piping), air
control, control of personnel, use of materials [59, 106],
paying special attention to specific technical aspects of
hygienic design at the detailed level of machines, materials
used, floors, piping, etc. But, one aspect of hygienic design
must not be neglected, as distinguished by Holah [87]: the
systematic analysis and evaluation of an overall factory
with the aim of segregating work areas to control hazards.
Segregation of work areas (or hygienic zoning, [59]) is
important for food processing industries. Van Donk and
Gaalman [191] have developed a decision aid that can be
used to evaluate the design or redesign of the layout of food
processing plants, explicitly taking into account hygiene of
the product and process and aiming to find the appropriate
segregation of work areas or different hygienic zones. This
usually must be considered as one of the aspects of
hygienic design [87]. The approach of Van Donk and
Gaalman [191] is inspired by principles of layout planning
and design, as developed in the field of production engi-
neering on the one hand, and the specific characteristics of
food processing industries and its products on the other
hand.
Ultra-clean and Aseptic Processing, Storage,
and Packaging
The Gram-positive Listeria monocytogenes is the pathogen
of concern in ready-to-eat meat and poultry products that
allow growth of the organism during storage, if exposed to
recontamination during slicing and packaging, without
posterior treatment [176]. In fact, L. monocytogenes con-
tinue being the number one target for control in ready-to-eat
meat and poultry products, considering its ubiquitous pres-
ence, potential to contaminate products after processing, and
the ability to multiply even under cold temperatures [183].
Types of antimicrobial interventions or hurdles used to
control pathogens in further processed meat and other food
products are of a physical, physicochemical, or biological
nature [90]. A recent regulation in the United States [74]
was established for the control of L. monocytogenes in
ready-to-eat meat and poultry products that may be con-
taminated after processing (during handling for slicing and
packaging). After this new regulation the industry must
choose one of three next alternatives: (i) application of a
post-lethality treatment (may be an antimicrobial agent) to
reduce or eliminate microorganisms on the product and an
antimicrobial agent or process to suppress or limit growth
of L. monocytogenes, (ii) application of a post-lethality
treatment (may be an antimicrobial agent) to reduce or
eliminate microorganisms on the product or an antimicro-
bial agent or process to suppress or limit growth of
L. monocytogenes, and (iii) a combination of sanitation and
microbiological testing programs for food contact surfaces
and holding of the product when results of testing are
positive [74, 176].
An advanced alternative for prevention of contamination
and control of L. monocytogenes (and other damage and
pathogen microorganisms) is ultra-clean and aseptic pro-
cessing (e.g., slicing), storage (Fig. 1), and packaging
technology (Figs. 3 and 4), involving a combination of
sanitation and microbiological testing programs for food
contact surfaces [166, 167]. But, it is very important to
understand the difference between non-hygienic, hygienic,
Fig. 4 Class 10.000 clean room closing a Class 100 clean room, for
ultra-clean packaging of fruit juices
94 Food Eng Rev (2009) 1:84–104
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ultra-clean, and aseptic processing and packing and their
consequences for processing and food safety [92].
Food Safety and Quality Standards
Quality standards have contributed to food safety [63].
During the last decade there was a strong trend towards
quality certification by large Western retailers. Private
safety control systems, standards, and certification pro-
grams are used to respond to higher consumer expectations,
because quality is no longer related to the product alone,
but also to the characteristics of the production and dis-
tribution processes, including the hygienic design [184].
Contrary to more general quality systems like HACCP
and ISO, systems used by retailers often cover more parties
in the chain [102]. ISO standards are international stan-
dards, enacted to achieve uniformity and to prevent tech-
nical barriers against trade throughout the world. The
standard extends the ISO 9001:2000 quality management
system standard, which is widely implemented in all sec-
tors, but does not specifically address food safety (www.
ISO.org; [184]). Demands regarding private food safety
and quality standards are best represented by three exam-
ples of systems used world-wide: Eurep-GAP, British
Retail Consortium (BRC), and Safe Quality Food (SQF).
Eurep-GAP is an organization of more than 20 large
European retailers and purchase organizations (e.g.,
AHOLD, TESCO). GAP stands for Good Agricultural
Practice. In 1998, the BRC, with participants such as
TESCO and Sainsbury, took the initiative to define com-
mon criteria for the inspection of suppliers of food prod-
ucts. The norms of the BRC are converging with HACCP
norms, although more attention is being paid to a docu-
mented quality management system, factory environments
and facilities (including hygienic design), product and
process control, and personnel. SQF aims at quality
assurance from a total supply chain perspective, including
food safety [184].
Fig. 5 Lay-out of air HEPA filters in a clean room Class 10.000 with access SAS
Food Eng Rev (2009) 1:84–104 95
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Advanced Systems for Active and Intelligent Packaging
Active Packaging
According to Brody et al. [19], active packaging, some-
times referred to as interactive or ‘‘smart’’ packaging, is
intended to sense internal or external environmental change
and to respond by changing its properties or attributes and,
hence, the internal package environment. From Robertson
[162] and Day [52] active packaging is defined as ‘‘pack-
aging in which subsidiary constituents have been deliber-
ately included in or on either the packaging material or the
package headspace to enhance the performance of the
package system,’’ including the safety, sensory, and quality
aspects of the food [52]. But, Kerry and Butler [97] prefer
to gather all forms of packaging where the package does
more than simply protect, store, and give information about
the product under the all-embracing term ‘‘smart packag-
ing’’ encompassing aspects of packaging design and
incorporation of mechanical, chemical, electrical, and
electronic systems, or a combination of these within the
package. But, active packaging is not synonymous with
intelligent packaging that senses and informs [51].
According to LoPrinzi [109], who assess the difference
between active (UV blocking, oxygen scavengers, moisture
controllers, ethylene absorbers, edible films, antimicrobial
agents), controlled (modified atmosphere, aseptic, retort,
sous-vide, biodegradable polymer), and intelligent (RFID,
electronic article surveillance, electronic shelf labels,
hybrid/interactive) packaging for foods and beverages, the
global market for such value-adding packaging (i.e., for
foods and beverages) will increase from $15.5 billion in
2005 to $16.9 billion by the end of 2008, reaching $23.6
billion by 2013, with a compound annual growth rate of
6.9%.
Application of Essential Oils from Plants to Improve
Safety of Packaged Food
In industrialized countries there is a high incidence of heart
disease and hypertension, and WHO has recommended the
reduction of salt content in foods [197, 198]. But, as salt is
a major barrier to the growth of certain pathogens in food,
its use is limited mainly to minimally processed foods that
require refrigeration, where cases of foodborne diseases
caused by psychrotrophic microorganisms such as Listeria
monocytogenes have increased [71, 78].
Therefore, it is necessary to investigate new methods of
manufacturing food to improve food safety, using hurdle
technology with natural antimicrobials that are safer and
healthier than synthetics. One possible solution is the use of
certain essential oils from plants that, at moderate doses,
have antimicrobial effects and are harmless to human
health; some even exhibit beneficial antioxidant and/or
antimutagenic effects [20].
The essential oils of plants (EOs) are complex mixtures
of different compounds. Many exhibit antimicrobial prop-
erties against bacteria, molds, and yeasts [3, 13, 17, 43, 83].
This property is attributed to the presence of aromatic
nuclei with a polar group [94]. In the food industry, their
main use is as food flavoring agents. Among the most
important EO components we can cite are carvacrol,
carvone, cinnamaldehyde, citral, p-cymene, eugenol, lim-
onene, menthol, and thymol [26]. Some components such
as estragole and methyl eugenol are toxic, however, and
their use in food is banned in the EU [41, 42].
EOs or their components are applied as antimicrobials
on food at industrial scale; in general, they are used in
larger doses than in lab tests to achieve the values of min-
imum inhibitory concentrations (MIC) or minimum bacte-
ricidal concentrations (MBC) [172, 174]. This increase can
be 2–100 times depending on the type of food [26]. The
antimicrobial effect of EOs generally varies with the
extrinsic and intrinsic factors of the food. The drop in pH
tends to increase the antimicrobial activity of the EOs due
to an increase in hydrophobicity of the active molecules of
the EOs, which increase the interaction with the membrane
lipids of the target microorganisms [94]. The high fat
content decreases the effectiveness of the antimicrobial
EOs, because if dissolved in lipids they are in less con-
centration, affecting their availability to attack the mem-
brane of target microorganisms in the aqueous phase of the
food [29, 124]. The high content of proteins has also been
identified as inhibitors of EOs [33, 48, 175]. However, it
has not been shown that carbohydrates have an inhibitory
effect on the antimicrobial activity of EOs [172]. Burt [26]
reviewed the literature describing experiments on appli-
cations of EOs to various kinds of foods, such as meats,
milk, fish dishes, vegetables, and fruits, and concluded that
the main EOs can be classified approximately according to
their antimicrobial activity as: oregano/clove/coriander/
cinnamon [ thyme[mint[ rosemary[mustard[cilantro/
sage. In the same way the main components of EOs can
be classified, from high to low activity, as: eugenol [carvacrol/cinnamic acid [ basil methyl chavicol [ cinna-
maldehyde [ citral/geraniol.
We can cite as examples foods with high EOs content,
such as bread with cinnamon [70] and milk flavored with
cinnamon and lemon [29]. But in general, the high sensory
impact that is present with EOs, at doses effective as anti-
microbials, limits their use in foods. For this reason, EOs
could be used by hurdle technology in synergistic combi-
nations with other physical or chemical agents to reduce the
dose needed and, thus, to reduce the sensory impact of EOs
and to increase acceptance of treated foods by the consumer.
Recently Cava et al. [29] introduced the concepts of Partial
96 Food Eng Rev (2009) 1:84–104
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Inhibitory Concentration (PIC) and Partial Bactericidal
Concentration (PBC), which consist of lower doses with less
sensorial impact in the foods than MIC and MBC. The doses
PIC and PBC may have an effect on improving food safety
when combined with other chemical or physical antimi-
crobial agents. The effect of EOs on various microorganisms
and food has been studied. Among the most studied micro-
organisms are the pathogens, L. monocytogenes, E. coli,
A. hydrophila, Salmonella spp., and Staphylococcus spp.
[88]. Among the spoilage microorganisms studied Alicy-
clobacillus acidoterrestris can be cited due to its impor-
tance, as this organism is extremely heat resistant and cannot
be eliminated by standard heat treatment used for canned
vegetable and fruit juices. Bevilacqua et al. [15] recently
suggested the use of EOs to prevent the germination of
A. acidoterrestris spores that have survived heat treatment.
When combined, EOs or their components, their antag-
onistic, additive, or synergistic effects can be observed. The
antagonistic effect means that the antimicrobial activity of
the mixture is lower than that of the components used on an
individual basis. The additive effect occurs when the activity
of the mixture is equal to the sum of activities of the com-
ponents. Finally, the synergistic effect occurs when the
activity of the mixture is higher than the sum of activities of
the components [49]. It has also been found that natural EOs
have a higher antibacterial activity than their individual
components or even their main components mixed, sug-
gesting the importance of the synergistic effect of the minor
components of the EOs [26, 77, 136].
Some examples of synergistic combinations of EOs and
other preservatives can be found in the literature. Syner-
gistic effects of sodium chloride combined with peppermint
EO were observed against S. enteritidis and L. monocyt-
ogenes [180]. A synergistic effect of powdered clove and
sodium chloride against E. aerogenes [195] has also been
described. Combinations of oregano EO and sodium nitrite
have also shown a synergistic effect for inhibiting the
growth and toxin production of C. botulinum types A, B,
and E [91]. The combination of nisin with carvacrol or
thymol has been described with synergistic effect for the
destruction of B. cereus; the antimicrobial activity of the
mixture increased when cells of B. cereus were heat-
shocked at 45�C, 5–40 min [146].
Encapsulation makes it possible to increase the effec-
tiveness of EOs and to decrease its sensory impact on
foods; for example, the encapsulation of rosemary EO has
proved to have more antimicrobial activity than rosemary
EO alone against L. monocytogenes in pork liver sausage
[142]. Eugenol and carvacrol encapsulated in micelles of
non-ionic surfactant have proved to be highly effective
against four strains of Listeria monocytogenes and E. coli
O157: H7, favoring the access of a greater amount of
antimicrobial on the surface of the bacteria [75, 145].
EOs are also more effective at low temperatures. Men-
doza-Yepes et al. [126] found that a mixture of EOs (DMC)
inhibited the growth of Listeria monocytogenes in soft
cheese stored in refrigeration. Cava et al. [29] found that
cinnamon and clove EOs were more effective in milk
incubated at 7�C than 35�C. Fitzgerald et al. [69] indicated
that vanillin is more effective in inhibiting the growth of
yeasts in soft drinks at 8�C than 25�C. The antimicrobial
action of EOs is based on the damage caused to the cell
membrane. This is due to its hydrophobicity, which allows
EOs to interact with the lipids of the cell and mitochondrial
membranes, disrupting their structures and increasing their
permeability. This increase in permeability can explain the
higher antimicrobial activity of EOs at low temperatures.
The phospholipids of the cytoplasmic membrane, growing
at 7�C, have a higher degree of unsaturation, which makes
the cell membrane more fluid, allowing the EOs to more
easily dissolve in the lipidic bilayer [29].
The application of EOs can be combined with the action
of mild heat to lower the temperatures of pasteurization,
thus obtaining foods more similar to natural foods with
better nutrient content and organoleptic characteristics.
However, the stability of EOs during the thermal process
should be studied as, for example, it has been found that
cinnamaldehyde becomes benzaldehyde at temperatures
close to 60�C when heated alone, although is stable for
30 min at 200�C when combined with eugenol or cinna-
mon leaf EO [70]. Karatzas et al. [95] found a synergistic
effect of carvone (5 mmol) and mild heat treatment (45�C,
30 min) on L. monocytogenes.
Karatzas et al. [96] found a synergistic effect of thymol
and carvacrol with HHP against L. monocytogenes. The
authors suggested that HHP treatment damages the cell
membrane of the microorganisms and enables a more
effective action of the EOs as antimicrobial on the damaged
membrane. Mohacsi-Farkas et al. [127] used high pressure
combined with oregano or thyme for the treatment of tomato
juice, lengthening the shelf life from 4 days to 3 weeks in
tomato juice stored at 15�C. More recently, Adegoke et al.
[1] found that moderately high pressures of 1800 kg/cm2,
combined with 150 mg/ml of alpha-terpinene for 1 h at
25�C, achieved a reduction of 6 log cycles in Saccharomyces
cerevisiae.
EOs could have synergistic effects with other nonther-
mal processes that cause damage to the cell membrane,
such as PEF, which allows inactivation of pathogenic and
spoilage microorganisms in food without significant loss of
flavor, color, and nutrients [10, 61]. PEF is equivalent to a
nonthermal pasteurization, which inactivates microorgan-
isms due to structural changes in the cell membrane,
resulting in the formation of pores and loss of viability of
the cells [151]. The use of PEF in combination with citric
acid or cinnamon bark increased the inactivation of
Food Eng Rev (2009) 1:84–104 97
123
Salmonella enteritidis and E. coli O157: H7 in apple, pear,
orange, and strawberry juices [132], Salmonella enteritidis
in tomato juice [133], and Salmonella enteridis, Listeria
monocytogenes, and E. coli O157:H7 in melon and
watermelon juices [134].
The antimicrobial activity of EOs is influenced by the
degree to which oxygen is available. This could be due to
the fact that when little oxygen is present, few oxidative
changes happen in the EOs; and/or when microbial cells
obtain energy by anaerobic metabolism, they are more
susceptible to the toxic effect of EOs. The antibacterial
activity of oregano and thyme EOs is favored heavily
against Salmonella typhimurium, and Staphylococcus
aureus when oxygen levels are low [143]. The lethal
effect of clove and coriander EOs on Aeromonas hydro-
phila in pork steaks stored at 2 and 10�C was more
effective in vacuum-packed samples than in air-packed
ones [177]. In a similar way the use of vacuum-packed
samples in combination with oregano EO had a syner-
gistic effect on the inhibition of L. monocytogenes in beef
steak spoiling microflora; with dose at 0.8% v/w of EOs,
the microbial population was reduced 2–3 log10. The
effect was greater in vacuum-packed samples with low
oxygen permeability films than in aerobically packed
samples or vacuum-packed ones with high oxygen per-
meability films [185]. The oregano EO delayed the
growth of spoilage microorganisms in fillets of meat
packed under MAP (40% CO2 ? 30% N2 ? 30% O2);
however, no distinct inhibition was found in beef packed
under air [173]. Valero et al. [188] found that table grapes
packed in active packages under MAP with eugenol and
thymol improved their sensory, nutritional, and functional
properties, as well as decreased the microbial contami-
nation. Chouliara et al. [38] found an additive preserva-
tion effect with oregano EO and MAP on shelf-life
extension of fresh chicken meat stored at 4�C. Rodriguez
et al. [164] assayed paraffin-based ‘‘active coatings’’ for
paper packaging materials intended to come into direct
contact with foods. This article was combined with EOs
of clove, cinnamon, and oregano and cinnamaldehyde-
enriched cinnamon EO. The shelf life of packaging
manufactured using fortified cinnamon EO was evaluated
against C. albicans and A. flavus, and was found to retain
its total inhibitory activity over the whole 71-day test
period. The efficacy of the coatings was tested in trials for
two varieties of strawberries and complete protection was
obtained during 7 days storage at 4�C; during this period
no fungal contamination or organoleptic changes were
observed in the strawberries. More recently, Serrano et al.
[171] reviewed the application of EOs with antimicrobial
and antioxidant properties in increasing the shelf life of
fruits packed in MAP.
Intelligent and Smart Packaging
Early ‘‘smartness’’ in packaging covered a number of
functionalities, including those from active packaging and
intelligent packaging. But, eventually there was an
important distinction between package functions that are
smart/Intelligent (Time–Temperature Indicators, Microbial
Growth Indicators, etc.) and those that become active
(Oxygen Scavenging, Anti-microbial, etc.) in response to a
triggering event [27]. In 2003, intelligent packaging (IP)
still was referred to as that which monitors the condition of
packaged foods to give information about the quality of the
packaged food during transport and storage [137]. Later,
Yam et al. [201] defined smart packaging devices as small,
inexpensive labels or tags that are attached to primary or
secondary packaging, to facilitate communication
throughout the supply chain.
However, the technologies and smart components
combining only the sensors and indicators, for example, the
freshness indicators and TTIs, giving the package the
intelligent function of monitoring, but not allowing a data
flow between the food chain agents, have limitations of use
[98]. With the Information and Communication Technol-
ogies (ICT), as RFID (Radio Frequency Identification), and
SAW (Surface Acoustic Waves) technologies, it is possible
to achieve a complete traceability and data flow without
line of sight between packages and the other supply chain
agents [14, 35, 40, 159].
There are many alternatives (options) available to
develop an IP, but the most prominent one is RFID tech-
nology, with which it is possible to have complete trace-
ability of food products [4].
RFID has been identified as one of the 10 greatest
contributory technologies of the 21st century [36]. In the
last several years, RFID has been one of the most studied
topics for application in warehouse management, supply
chain management (SCM), and logistic fields. The impact
of this technology in the supply chain has been evaluated
for years. Due to its developed infrastructure, it is con-
sidered as the first option in the development of the IP
using ICTs [140].
Smart packaging development, including active, con-
trolled, and intelligent packaging, must be considered as a
part of multidisciplinary food safety engineering, as it
involves different active and intelligent packaging systems
(oxygen scavengers, carbon dioxide scavengers/emitters,
ethylene scavengers, preservative releasers, ethanol emit-
ters, moisture absorbers, flavor/odor absorbers, temperature
control packaging, temperature compensating films, RFID
and SAW tags, etc.) that must be engineered (different
materials, bio-polymers, nano-matters, Eos, and devices in
contact with food) to achieve adequate food safety [46, 52].
98 Food Eng Rev (2009) 1:84–104
123
Conclusions
This review has included the main knowledge blocks that
constitute Food Safety Engineering: (i) predictive microbi-
ology, applied to traditional and new food products and
processing technologies, (ii) advanced food contaminants
detection methods, to be applied during food processing and
distribution along the supply chain, (iii) advanced process-
ing technologies and safety, (iv) advanced systems for
re-contamination control in food processing, storage and
packaging, including barrier technology, hygienic design
and zoning, ultra-clean and aseptic processing, storage and
packaging, and quality standards, and (v) advanced systems
and materials for active, controlled and intelligent packag-
ing, paying special attention to the use of EOs.
It is deduced that the complexity of Food Safety Engi-
neering, as an emerging specialization involving the
application of different engineering sciences to address
microbial and chemical safety challenges, justifies the need
for a specific curricula for studying this specialty, as
developed under the Food Engineering degree. Thus, dif-
ferent universities should propose that Food Safety Engi-
neering be established as part of a degree program,
including research in the above knowledge blocks, and the
study of regulations of authorities for food safety and
security, to be applied to all materials and technologies
entering in contact with foods.
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