Thermal and Alternative Food Processing Technologies

Dr. Sirichai Songsermpong

Dept. of Food Science and Technology

Kasetsart University

alternative technologies

Microwave and Radio Frequency

Ohmic and Inductive Heating

High Pressure Processing

Pulsed Electric Field

Irradiation

High Voltage Arc Discharge

Pulsed Light

Oscillating Magnetic Fields

Ultraviolet Light

Ultrasound

overview

review of thermal and alternative technologies

discussion of principles that apply to all of the technologies, focusing on reaction kinetics

research needs are identified

thermal processes

Commercial sterilization

batch retort

batch retort

batch retort

Advantages

Cost of equipment

Accept different container size, type and product flexibility

Equipment failures for one retort don’t stop entire production line

Disadvantages

High energy cost

High labor cost

continuous systems

continuous systems

hydrostatic retorts

hydrostatic retort

Cans enter the hydrostatic retort in a “stick”

hydrostatic retort

continuous retort

Advantages

Low labor (15-40% less labor) and energy (25-50% less steam) cost per unit produced

Disadvantages

Cost of equipments

Limited to metal containers of one size

Equipment failure stops the entire line

Can only process one type of food at a time

Reaction kinetics

Establishing the mechanisms of a reaction

Obtaining experimental rate data

Correlating data by equations(kinetic parameters)

Designing food processes (heat transfer, electric fields,…)

Reaction rate and rate constant

Reaction rate

Rate constant

dt

dCr

...),,(

),,(),,(

),,,,(

BA

BA

BA

CCetcPTkr

etcCCfetcPTkr

etcPTCCfr

r = k C (first-order kinetics)

log C/Co

Salmonella in ground beef at 57.2 °C

(Goodfellow and Brown, 1978)

Ckdt

dC

tDC

C 1log

0

tkC

C'log

0

D-value

Decimal reduction time

C

CDt 0log

DDt 1

10log

DDt 10

100log

Microwave, ohmic and inductive heating

The energy absorption from microwaves and electric currents can raise the temperature of the food high enough to inactivate microorganisms for pasteurization or sterilization.

A number of studies suggest that the thermal effect is the essential contributor to the destruction of microorganisms as well as the degradation of vitamins, etc

Reported non-thermal effects are likely to be due to the lack of precise measurements

Microwave, ohmic and inductive heating

Thermal D-values provide a sound basis for development of processes for the microwave energy and electrical resistance (ohmic and inductive) technologies

High pressure and electric field

The concept of D-value can describe the microbial population reduction at a constant pressure or constant electric field.

D(P), D(E)

assumptions

a) The basic model assumes a first-order relationship between microbial population and time

b) D-value describes the microbial population reduction at a constantand defined temperature, pressure and/or electric field.

Research needs

Non-linear models

There are considerable discussions about the appropriateness of using a first-order model to describe the reduction in microbial population for all preservation technologies

Non-linear models

Demonstration of how forcing a straight line through a concave semi-logarithmic survival

curve can result in an over or under estimate of an organism's resistance to a lethal agent

(Peleg, 1999)

Non-linear models

Alternative models are being developed to explain microbial inactivation kinetics when the linearity of the data is questionable (Peleg and Cole 1998; Anderson 1996).

If there is evidence of a non-linear model, different parameters need to be identified for prediction purposes.

Non-linear models

Listeria monocytogenes in chicken meat at 70 °C

(Murphy et al., 2000).Salmonella in egg yolk (Michalski et al., 1999).

nbtC

C

0

log

Peleg’s model (1998)

assumptions

a) The basic model assumes a first-order relationship between microbial population and time

b) D-value describes the microbial population reduction at a constanttemperature, pressure or electric field.

Constant pressure

High pressure processing (HPP), also described as high hydrostatic pressure (HHP), or ultra high pressure (UHP) processing, subjects liquid and solid foods to pressures between 100 and 800 MPa.

HPP acts instantaneously and uniformly throughout a mass of food independent of size, shape, and food composition. Thus, package size, shape, and composition are not factors in process determination

Constant temperature?

Cold point

Heat penetration study

Data Acquisition System

Thermocouple

Typical heat penetration result

0.0

50.0

100.0

150.0

200.0

250.0

300.0

0 20 40 60 80 100 120 140

Time (minutes)

Tem

pera

ture

(d

eg

F)

PRODUCT TEMPERATURE

MEDIUM TEMPERATURE

Heating and Cooling Profiles

processing time

direct steam injection

tubular heat exchanger

Triple tube

Double tube

Triple tube

Double tube

Indirect: plate heat exchanger

Example: pasteurization

Pathogens

30 min, 63 C

D = 2.5 min

Vitamins

30 min, 63 C

D’ = 120 min

tDC

C 1log

0

Example: pasteurization

Pathogens

71 C

D = 0.021 min

Same lethality

Vitamins

71 C

D’ = 250 min

HTST pasteurization systems

155 degrees F (69 degrees C) for 30 minutesEggnog

280 degrees F (138 degrees C) At least 2 secondsAll milk products

Ultra-Pasteurized (Extended Shelf Life)

180 degrees F (83 degrees C) for 15 secondsEggnog

175 degrees F (80 degrees C) for 25 secondsIce cream mix

175 degrees F (80 degrees C) for 25 secondsCream

161 degrees F (72 degrees C) for 15 secondsMilk

HTST- Pasteurization

155 degrees F (69 degrees C) for 30 minutesIce cream mix

150 degrees F (66 degrees C) for 30 minutesCream

145 degrees F (63 degrees C) for 30 minutesMilk

Batch Pasteurization

155 degrees F (69 degrees C) for 30 minutesEggnog

280 degrees F (138 degrees C) At least 2 secondsAll milk products

Ultra-Pasteurized (Extended Shelf Life)

180 degrees F (83 degrees C) for 15 secondsEggnog

175 degrees F (80 degrees C) for 25 secondsIce cream mix

175 degrees F (80 degrees C) for 25 secondsCream

161 degrees F (72 degrees C) for 15 secondsMilk

HTST- Pasteurization

155 degrees F (69 degrees C) for 30 minutesIce cream mix

150 degrees F (66 degrees C) for 30 minutesCream

145 degrees F (63 degrees C) for 30 minutesMilk

Batch Pasteurization

Batch and HTST times