heat processing

8/13/2019 Heat Processing

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FSM 3001

HEAT PRESERVATION OF FOODS



HEAT TRANSFER

• The transfer of energy in the form of heat intoor out of a product

– Heating

• Pasteurization

• Boiling

– Cooling• Freezing



TYPES OF HEAT TRANSFER

• Radiation

• Convection

• Conduction



Principle of Heat Transfer

• Conduction – from one particle to another by contact

– food particles in can do not move

• Convection – movement inside can distributes heat

• Radiation – energy transfer through a medium which itself is

not heated



CONDUCTION



Heat Transfer

product

Conduction

Heating medium

Convection

tank wall



• Increase palatability –Baking, broiling, roasting (dry heat)

–Frying in oil (160-190 °C) –Boiling, stewing in boiling water

OBJECTIVES OF HEAT

PROCESSING



HEAT INDUCED CHANGES

• Desirable

– Destruction of microorganisms

– Destruction or inactivation of enzymes

– Alteration of color, flavor, texture

– Improved digestibility



HEAT INDUCED CHANGES

• Undesirable – Degradation of nutrients

– Degradation of sensoryattributes

• Color

• Flavor

• Texture



COOKING OR HEATING FOODS

– kills some microorganisms

– destroys most enzymes

– improves shelf life

– does not indefinitely preserve



OBJECTIVES OF HEAT

PROCESSING

• Increase storage life - minimize foodborne

diseases

– Blanching

– Pasteurization

– Sterilization = “commercial” sterilization



BLANCHING

A process where food is briefly heated by

1) Immersing in boiling water

2) Steaming3) Microwave

… and then rapidly cooled to stop cooking



BLANCHING

Blanching is often used as a preliminary

step for freezing, canning, or dehydration



PURPOSES OF BLANCHING

• Inactivate enzymes that can cause

• Deterioration in flavor, texture,color, and nutrients during

storage• Reduce number of microorganisms

• Remove air from tissues

• Make food more compact

• Enhance color



PASTEURIZATION

• Low order heat treatment at temperatures below boiling.

• Destroys pathogenic microorganisms.• Extends shelf life by destroying microorganisms

& enzymes (milk, fruit juices, beer, and wine)

• Products contain many living organisms capable

of growth, thus limiting shelf life.



PasteurizationMethod Processing Parameters Approx. Shelf Life

Batch 63ºC for 30 min. ~ 12 days

High temperature 71.5 ºC for 15 sec. ~ 14 days

Short time (HTST)

Ultra pasteurized 140 ºC for 2 sec. & ~ 45-60 days

conventionally packaged

Ultra high temp. 140 ºC for 2 sec. & ~ 6 mo. @ room temp.

(UHT) aseptically packaged ~ 1 yr. @ refr. temp.



PASTEURIZATION

• Destroys pathogenic microorganisms in

vegetative state – Juices, milk, liquid eggs

• Extend product shelf life by reducing microbialand enzymatic spoilage

– Beer, wine and other alcoholic drinks

– Fruit juices

– Pickles



SUMMARY

• Pasteurization - Temps < 100oC (212oF)

– Destroys pathogenic microorganisms – Extends product shelf life (but not extensively)

– Ex: milk, beer, fruit juices, liquid eggs• Blanching

– Primarily used for fruits & vegetables

– Deactivates enzymes

– Kills some bacteria



COMMERCIAL

STERILIZATION

• Destroys both vegetative and spores of

pathogenic organisms

• Reduces nutritional value

• Causes loss of organoleptic properties



STERILIZATION

Complete destruction of microorganisms

• 121ºC for 15 minutes or more

• Can be considered to be a very harsh treatment• Used to sterilize foods in cans or containers



Commercially “Sterile” Foods

All pathogens & toxin-forming organisms are

destroyed as well as other organisms that

could cause spoilage under normalconditions.



Commercially “Sterile” Foods

• May contain a small number of heat-resistant

bacterial spores, but these will normally not

multiply in the food.

• Shelf life of two years or more.



SUMMARY

• Sterilization


• 121oC (250oF) for 15 minutes (internal temp)

• Commercially Sterile

All pathogenic & toxin-forming organisms are

destroyed (applies to most preserved foods)



Conventional Retort Processing and

(Non-Aseptic) Packaging

Product Package

(FORM)

Fill Seal

“Sterilization”

(Heat)

ShelfStable

Product



Aseptic Packaging

• Food is sterilized outside the can• Placed into a sterile container and sealed

under aseptic conditions

• Paper and plastic packaging materials most

commonly used

• Most suitable for liquid-based food products

SELECTION CONDITIONS ARE



SELECTION CONDITIONS ARE

BASED ON :

• Nature of the food (pH, composition, viscosity,heat capacity, other components)

• Storage conditions following thermal

processing• Heat resistance of organisms

• Heat transfer characteristics• Initial load of organisms

• Post-processing packaging



pH CONSIDERATIONS

• HIGH ACID FOODS (pH <3.7)

– Spore forming bacteria do not grow

– Depends on either inactivation of yeasts

and molds or maintenance of anaerobic

conditions



pH CONSIDERATIONS

• Acid foods (3.6<pH<4.5) –Based on outgrowth of facultative

anaerobes• B. Coagulans

• B. Thermoacidurans• B Polymyxa



Low acid means higher pH

pH CONSIDERATIONS

• LOW ACID FOODS (pH>4.5)

– Cl. Botulinum can grow

– Low acid canned foods ideal for growth and toxin

production

– Control of spoilage organisms requires more heat -B. Stearothermophilus used as reference organismfor spoilage



Processing Requirements Based Upon

Acidity (pH)

Acidity

Class pH

Food

Group

Spoilage

Agent

Processing

Required

LowAcid 7.0

6.0

MeatFish

Milk

PoultryVegetables

Soups

MesophilicSpore-forming

Anaerobs

Thermophiles

High Temp116o-121

oC

240o-250

0F





Acidity (pH)

AcidityClass pH FoodGroup SpoilageAgent ProcessingRequired

Acid 4.5 Fruits

Berries

Aciduric,

spore-formingand non spore-

forming

bacteria

Boiling

water100

oC

(212oF)

F d P i R i t B d



Food Processing Requirements Based

Upon Acidity (pH)

Acidity

Class pH

Food

Group

Spoilage

Agent

Processing

Required

High

Acid

3.0 Pickled

foods,

jams, jellies

Yeasts, molds Boiling

water

100

o

C(212oF)



CANNED

FOODS

THERMALLYPROCESSED

FOODS



Canning : Historical Perspective

• Late 1700’s

• France was at war with most of Europe

• French troops ate salted meat & bread

• Other food could not be kept fresh

• Soldiers were dying of scurvy and other disease

because of their diet• Needed some nutritious food



Canning : Historical Perspective

• Napoleon offered a prize of 12,000 francs towhomever could devise a method to preserve

food

• Nicolas Appert, a French confectioner& chef

won the prize is 1809



Heat Preservation

• Appert put food in cork stoppered, wide

mouth bottles and submerged them in boiling

water for several minutes

• Published a report: “The art of preserving

animal and vegetable substances for manyyears.”



THE

PROCESS

OF

CANNING

FRUITS



CANNED FRUIT

PROCESSING STEPS

WASHING AND CLEANING

GRADING

PEELING

BLANCHING

CAN FILLING

SEAMING

RETORTING

COOLINGPACKING

STORAGE AND DISTRIBUTION



THERMALLY PROCESSED FOODS



THERMALLY PROCESSED FOODS

• The primary objective of thermal processing of

food is to destroy the most heat resistant pathogenic spore forming organism, which is

clostridium botulinum

• The secondary objective of thermal processing

of food is to destroy spore forming organisms

that cause spoilage. These organisms aregenerally more heat resistant than the pathogenic

spore formers

MICROBIAL DESTRUCTION BY



MICROBIAL DESTRUCTION BY

HEAT

• Spores are much more resistant that vegetative cells

• Lethality terms

– D value - time at a given temperature to cause a one

log cycle decrease in cell numbers – Z value- temperature required to give a one log

cycle decrease in the D value

– Fo value - time at 121 oC to give a 12 log cycle

decrease in the spore or cells of a given organism



Thermal Death Curves• Heat kills bacteria logarithmically

– i.e. If 90% are killed in the first minute ata certain temperature, then

– 90% of those remaining alive will dieduring the second minute, and

– 90% of those remaining alive will die

during the third minute, etc.

Spores are more heat resistant than vegetative cells



1,000



1

10

100

1,000

210 230 250

TEMPERATURE (o F)

1 ,0 0 0 / m l

1 0 ,0 0 0 / m l

1 0 0 ,0 0 0 / m l Killing

time(min)

Thermal death curves for bacterial spores

at different initial concentrations



UHT



Ultra High Temp

Pasteurization

Temperature

Profile

Of Pasteurization

And

UHT



°



D VALUES AT 121°

C

• Bacillus stearothermophilus (flat sour)

– D value = 4.0 to 5.0

• Clostridium botulinum

– D value = 0.1 to 0.2 min

MICROBIAL DESTRUCTION BY HEAT



MICROBIAL DESTRUCTION BY HEAT

• Factors affecting heat inactivation

– pH

– Time and temperature

– Viscosity – Product type

– Convection versus conduction

– Package size

– Organism



HIGH/LOW ACID FOODS

Foods can be classified on the basis of pH

>pH 4.5 ARE LOW ACID FOODS

<pH 4.5 ARE ACID FOODS

<pH 3.7 ARE HIGH ACID FOODS

CONVECTION VERSUS CONDUCTION



CONVECTION VERSUS CONDUCTION

HEATING

• Fo is determined at the slowest point in the

package

• Fluid products are heated mainly by convection

• Products with high viscosities or with

particulates are heated by conduction

Thermocouple Placement at



e ocoup e ace e t at

Cold Point in Can

Determining Process Time and Lethality



1. Heat-sensing thermocouples placed at the cold

spots in the can

2. Measure come-up times for the heat process insidethe can as well as the cooling periods

3. Total lethality of the heat process represents a

summation of the lethal effects of changing

temperatures with time during the entire retort

operation4. The required heat treatment will be different

depending on the retort, the size and shape of the

containers, and the composition of the food.

Degrees of Heat Treatment



Degrees of Heat Treatment

• Sterilization


• 121oC (250oF) for 15 minutes (internal temp)

• Commercially SterileAll pathogenic & toxin-forming organisms are

destroyed (applies to most preserved foods)



Selecting Heat Treatments

• Heat that is sufficient to destroy all

microorganisms and enzymes is detrimental

to other food quality factors such as:

• Color• Flavor

• Texture

• Nutrition

• Consistency



Time/temperature combination required toinactivate the most resistant microbe

• The most heat resistant pathogen in canned

foods is Clostridium Botulinum (botulism) – Therefore, must use time/temperature

combination adequate to kill this species



Assumptions of Safety

• Unknowns in raw foods, especially thosewhich are low acid:

– types of microbes present

– number of microbes present

• Therefore assume:

– C. Botulinum to be present in large numbers

INOCULATED PACK STUDIES



Method

A known substantial population of Clostridium strain

is inoculated into cans of food that are then processed

in a retort. After processing, the cans are stored at

temperatures favorable for outgrowth of any

surviving spores, and checked periodically for growthand spoilage, such as bulging cans due to gas

production.

To Check the Effectiveness of Thermal Processing




Acidity (pH)

AcidityClass pH

FoodGroup

SpoilageAgent

ProcessingRequired

Low

Acid

7.0

6.0

Meat

FishMilk

Poultry

Vegetables

Soups

Mesophilic

Spore-formingAnaerobs

Thermophiles

High Temp

116o-121oC240

o-250

0F


Acidity (pH)



Acidity (pH)

Acidity

Class pH

Food

Group

Spoilage

Agent

Processing

Required

Acid 4.5 Fruits

Berries

Aciduric,

spore-formingand non spore-

forming bacteria

Boiling

water100

oC

(212oF)

Food Processing Requirements Based



Upon Acidity (pH)

AcidityClass pH

FoodGroup

SpoilageAgent

ProcessingRequired

HighAcid

3.0 Pickledfoods,

jams, jellies

Yeasts, molds Boilingwater

100

o

C(212oF)

HEAT TRANSFER



• Every food particle inside a can must reach

the critical temperature for the required time• Factors affecting heat penetration include:

size of canshape of can

consistency of the food item (thick or thin)

nature of the food (particulate vs liquid)

Protective Effects of



Food Constituents

• Sugar protects bacterial spores in canned

fruit

• Starch & protein protect spores

• Fats & Oils protect bacterial spores

Examples of Process Times



p

Initial Temp 307x409 cans

ProductoC

oF

Min @

116

o

C(240

oF)

Min @

121

o

C(250

oF)

Green Beans 21 70 21 12

French Beans 21 70 40 20Corn, cream 71 160 100 80

Corn, whole 38 100 55 30

Peas 21 70 36 16

Pumpkin 71 160 80 65



Time-Temperature Combinations From thermal death curves, the following

time/temperature treatments yield the same

microbe killing effect:

0.78 min @ 127oC 10 min @ 116oC 1.45 min @ 124oC 36 min @ 110oC

2.78 min @ 121oC 150 min @ 104oC

5.27 min @ 118oC 330 min @ 100oC

Heating Before or



After Packaging• After:

– simplest

– oldest form of preservation using heat

• Before: – less damaging to food

– requires aseptic packaging

Temperature - Pressure Relationship



10 psi = 116 °C

15 psi = 121 °C

20 psi = 127 °C

Retort



Retort



Heating Food Prior to Packaging

• Pasteurization (liquid products)

• Batch

– Product in steam-jacketed kettle heated to specified

temperature and rapidly cooled (for example, milk heated to 63oC for 30 min)

• Continuous

– High Temp Short Time (HTST)

– For example, Milk heated to 71 oC for 15 sec.

Aseptic Packaging



• Food is sterilized outside the can

• Placed into a sterile container and sealed

under aseptic conditions

• Paper and plastic packaging materials mostcommonly used

• Most suitable for liquid-based food products



CAN MORPHOLOGY



RETORT POUCH



• Metal can sizes are derived from

diameter



nominal outside dimensions andexpressed in inches

• The custom is to use a conventional

method in which three-digit numbers

are used to express each dimension.

• The first digit indicates the numberof whole inches in a dimension

• The second and third digits indicate

the fractional inches as sixteenths of

an inch.

height



• The first three-digit number describing a round canindicates the diameter measured across the outside

of the chime on the seamed end.• The second three-digit number indicates the overall

height of the can with one end on.



• For the dimensions of oval, obround, or obrotund cans,

outside dimensions are used, the dimensions of the opening

being stated first, followed by the height.

• There are three sets of figures, the first two being the long

and short axis of the opening.

• Their interpretation in inches and sixteenths of an inch is

the same as with round cans.• An oval can might have the size give as 402 x 304 x 612,

which would mean that the oval opening was 4-2/16 x 3-

4/16 inches and the height was 6-12/16 inches.

Three-piece Food Can Dimensions

Imperial Size Metric Size

(mm)

Metric Volume

(ml)



202 x108 52 x 38 70

202 x 213* 52 x 72 140

202 x 309 52 x 90 180

52 x 134 250

211 x 202 66 x 54 155

211 x 205 65 x 59 175

211 x 301 65 x 78 235

211 x 400 65 x 102 315

211 x 414 65 x 124 385

300 x 108 73 x 38 125

300 x 201 73 x 52 185



Why Can Foods?



SOME FACTS ON CANNING

• Many vegetables lose some of their vitamins



when harvested.

• Nearly half the vitamins may be lost within a

few days unless the fresh produce is cooled or

preserved.

• Within 1 to 2 weeks, even refrigerated produceloses half or more of some of its vitamins.

• The heating process during canning destroys from one-third

to one half of vitamins A and C thiamin and riboflavin



to one-half of vitamins A and C, thiamin, and riboflavin.

• Once canned,additional losses of these sensitive vitamins are

from 5 to 20 percent each year. The amounts of other vitamins,

however, are only slightly lower in canned compared with fresh

food.

• If vegetables are handled properly and canned promptly after

harvest, they can be as or more nutritious than fresh produce

sold in local stores.

What Are the Ridges Often

Seen Around the Body of a

C ?



Can?

• Ridges or "beads" are designedto give added strength to the can

body

• The "rings" around the can ends

are designed to allow forexpansion of the ends during heat

processing without causing

permanent distortion.

How Long Can I Keep Canned Foods?

• Manufacturers advise two years from time of manufacture.

It i d ti t th ithi t l th f



• It is good practice to use them within twelve months of

purchase to enjoy maximum flavour, appearance and

nutrition.

• Always store canned foods in a cool, dry place.

• Canned foods must be permanently marked in such amanner as to identify the manufacturer and to trace the

batch or time of manufacture. This information is usually

displayed via embossing or inkjet on the can ends and

might be encoded.

How Do I Know Whether the Food in the

Can Is Still Good?



Can Is Still Good?

• If any can is slightly swollen, bulging or leaking

return it to the point of purchase.

• Small amounts of rust on a can should not affect

the contents but a badly rusted can should not be

used.

• The common sense practice of testing by smelland sight after opening any packaged food product

should be followed.



Do Canned Foods Contain Preservatives or

Not?



Not?

• Heat sterilisation of the contents of the can in the

food canning process means that no chemical

preservatives are needed or used.

• Anything added to canned food is simply toenhance texture, taste or flavour.

• A wide range of low or no-sodium and reduced

sugar or sugar-free varieties are available if

preferred.

What Food Additives Are Used in

C d F d ?



Canned Foods?

Sugar and salt are added to some canned

foods. These are added to suit people's tastes -no canned foods need any form of

preservative.

Are Artificial Colours and Flavours Used in



Are Artificial Colours and Flavours Used inCanned Foods?

Artificial flavours and colours may be used in

some products. Only those listed in the Food

Standards may be used.

Can I store unused food in its can?



• Canned foods don't contain preservatives.

• Once opened, the contents of the canshould be treated just as you would fresh

food.

• Any unused portion must be transferred to

a plastic or glass container, cover and store

in the refrigerator.

I'm Concerned About Food Poisoning. How

Safe Is Canned Food?• Very safe



• Very safe

• The cans are first checked for quality before they are filled

with food prepared by Good Manufacturing Practice (GMP).

• Each can is sealed and heated under pressure to above

100°C.• Heating is to a predetermined temperature for a specified

time is so that each can becomes like a little pressure cooker

ensuring that organisms, or bacteria called which cause food

poisoning, are killed.

Is there a difference between the nutritional

value of fresh and canned food?



value of fresh and canned food?

• There is a perception that "fresh is better"

• The canned food industry commissioned research

to establish whether this perception is true or not.

• The studies showed that there is very little

practical difference in the nutritional value of

canned foods compared with their fresh

equivalents.

Why Are Cans Never Completely Full?

Wh l d i h t d d i i i t l



• When a sealed can is heated during processing an internal

pressure develops.

• If a can was completely filled this might cause excessive

strain and subsequent distortion of the can ends as there

would be no room for expansion of the contents.• The consumer always gets the correct net content weight

stated on the label because allowances are made for this socalled "headspace".



DISADVANTAGES



• Loss of quality due to thermal degradation of

– Color

– Flavor

– Texture



Microwave Heating



• Eliminates temperaturegradients

• Rapid heating• Limited packaging (no

metal containers)



Temperature distribution of microwave heating 2% milk cylinder

MICROWAVE HEATING OF EGG



Domestic Oven

Heating Of Poultry

Carcass



•Considerable variation (up to

30°C) in final surfacetemperatures at the same

defined positions on replicate

carcasses•Average temperature

difference of up to 61°C

between different points on

the carcass



STERILIZATION EQUIPMENT

• UHT sterilizers



– Combined with aseptic packaging provides

for less heat induced changes• Retorts (pressure processors)

– Still – Rotary sterilizer

– Hydrostatic cooker (pressure provided by a40-50 feet of head pressure)

Heating of Food in Cans



• Still Retort

– Max temp of 121oC to prevent food damage nearcan wall

– Long cook time

• Agitating Retort

– Shorter cook time

– Less food damage

Retort



Hydrostatic Retort



• Continuous flow of cans• Uses hydrostatic head

to control pressure• Is an agitating system



Pasteurizer



HIGH TEMPERATURE SHORT TIME (HTST)

Homogenized milk is

bro ght to 72 75 °C for 15



brought to 72-75 °C for 15

seconds and then chilled to4 °C in the High

Temperature Short Time

(HTST) process, to ensure

a pasteurized product with

a life span of 8 to 10days.



Scraped Surface Heat Exchanger



PROCESS EFFECTS

High Heat treatment Inactivation of enzymes, destruction of

microorganisms; browning; flavor changes;

texture changes

Freezing Minimize of microbial growth; slowing the rate



of chemical rreactions; disruption of cellular

material (softening); precipitation of proteins onthawing

Packaging Improper packaging or packaging materials can

permit the transfer of oxygen into the product

and cause off flavors; moisture transfer into

packaged foods can cause caking, increase in

the rate of chemical reactions and permit

enzymes to act of food constituents

High shear pumping Can cause size reduction; production of foams

(either desired or undesired); disruption of

protein structure; activation of enzymes in some

cases.



THE END

heat processing

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