Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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myofibrillar protein solubility, lower water-binding

capacity, and somewhat tougher and drier texture.

In these studies, samples were thawed after storage

periods of 2–3 days at 20



C, so the relationship

between freezing rates and storage life was not inves-

tigated.

0023 The results on freezing rate are scientifically very

interesting, but in industrial practice, most meat is

air-frozen in the form of large individual pieces or

cartons containing smaller portions. In commercial

situations, freezing rates of 0.5 cm h

1

in the deeper

sections would be considered ‘fast,’ and there would

be considerable variation in freezing time within the

meat. The mutton samples frozen in these studies

were much smaller (77.6 g in weight) than most

commercial products. Even with such small samples,

there was no significant difference in drip after 48 h

between cryogenic freezing at 90



C and a walk-in

freezer operating at 21



C(Table 2).

0024 Experiments have been carried out on freezing

samples similar in size to a domestic joint. There

was no significant difference in drip loss from 700-g

samples of pork l. dorsi frozen in air at 20 or

80



C. At 20



C, samples required approximately

6 h to pass from 1to6



C, compared with half this

time at 80



C. Average drip losses were 3.7% at

20



C and 5.2% at 80



C. In commercial situ-

ations, freezing times typically range from tens of

hours to a few days. Freezing rates are therefore

outside the values that influence drip potential.

0025 Drip loss in frozen storage has been shown to

increase with storage time and increase in storage

temperature. After approximately 42 and 63 days,

drip from beef stored at 10 or 15



C had reached

80 and 90%, respectively, of its maximum. At

25



C, it required over 120 days to reach the 80%

value.

0026 Drip loss during thawing from ground beef patties

was also found to increase with the length of time the

patties had been in frozen storage. For higher-fat-

content samples, drip loss increased from 1.8% in

fresh samples to 12.5% after 20 weeks in storage.

Higher drip losses in thawing were found for samples

stored at 12.2



C than lower temperatures. How-

ever, there was no difference between storage tem-

peratures of 23.3 and 34.4



Flavor Changes

0027No marked changes in fruit flavor occur on freezing

except after an extended process at elevated tempera-

tures. Changes in flavor constituents of frozen fruit

are generated during prolonged storage and increase

as the storage temperature is increased. The first sig-

nificant change in stored frozen fruits is a loss of fresh

aroma. After this, some off-flavors may develop that

are dependent on the type of fruit. Some fruits are

known to be more stable than others, but the exact

reason is not known.

0028Enzymes in fruits and vegetables are slowed down,

but not destroyed, during freezing. If not inactivated,

these enzymes can cause color and flavor changes as

well as a loss of nutrients.

0029Enzymes in vegetables are inactivated by blanch-

ing, then rapidly cooled in ice water to prevent

cooking. Blanching is essential for top-quality frozen

vegetables.

0030Another type of chemical change that can take

place in frozen products is the development of rancid,

off-flavors. This can occur when fat, such as in meat,

is exposed to air for a certain period of time.

0031Species has an influence on rancidity development.

Investigations have been carried out on rancidity de-

velopment in cooked and uncooked ground meat

patties made from chicken, beef, or pork. In one

study, the TBA (thiobarbituric acid) values in un-

cooked patties were higher in beef than in those

made from either pork or chicken (Figure 1). Levels

in chicken patties did not change appreciably during

150 days, storage at 20



C. After 150 days, the TBA

values in beef were approximately 7 times higher than

those in chicken, and the values in pork were 4–5.5

tbl0002 Table 2 Drip loss (%) from 77.6-g samples of Mm. longissimus lumborum et thoracis frozen under different methods and thawed

at 4



Freezingconditions Freezing time to 2.2



C Freezing rate (cm h

1

)Storagetimeat20



48 h 2.5months

Cryogenic  90



C 15 min 6.4 3.34

9.49

Cryogenic  65



C 22 min 4.4 4.70

a,b

9.72

Blast freezer  21



C 1.83 h 0.55 5.53

12.74

Walk-in freezer  21



C 1.88 h 0.53 4.71

a,b

13.18

Domestic freezer  25



C 1.96 h 0.51 5.26

11.72

From Sacks B, Casey NH, Boshof E and van Zyl H (1993) Influence of freezing method on thaw drip and protein loss of low-voltage electrically stimulated

and non-stimulated sheeps’ muscle. Meat Science 34: 235–243.

a, b, c, d, e, f

The same letters indicate no statistical differences.

2738 FREEZING/Structural and Flavor (Flavour) Changes

times as high as those in chicken. Cooked chicken

patties had a higher lipid oxidation potential than

cooked beef or pork patties.

0032 Other studies have found a temperature and species

interaction for pork and beef. In experiments, the

practical storage life (PSL) and high-quality life of

pork were superior to beef at 5



C, but at 10 and

20



C, the storage life of beef was much longer. In

other trials where more than one species was com-

pared, storage times were not fully presented, or

direct comparisons were not possible.

0033 It seems fair to conclude that most work indicates

differences in frozen storage life between species.

However, we currently lack the understanding to use

data on the frozen storage life of one species under a

given condition to predict the likely storage life of

other species under that condition.

0034 Animal-to-animal variation is believed to cause

wide variations in storage times. Investigations in

New Zealand have found that animal-to-animal vari-

ation can lead to storage-life differences as great as

50% in lamb but do not give any definite reason for

this variation. Two trials were carried out in which

lamb was stored at 5



C. In the first trial, the lamb

was judged rancid after 20 weeks, and in a duplicate

trial using identical temperature, processing, and

packaging conditions, the lamb was found to keep

for 40 weeks. The only variation that could be deter-

mined was that different animals were used in the two

trials.

0035 Processing of meat prior to freezing generally

results in a lengthened storage time. It has been

found that the amount of TBA-reactive substances,

in prerigor cooked boar, did not change during 3

months, storage at 20



C. Heating prior to freezing

can result in a 50% longer PSL for sausages and is

thought to be due mainly to inactivation of some

of the enzymes present or, possibly, inactivation of

the catalytic activity of hemoglobin. However, the

heating process may be critical, since muscles cooked

at higher temperatures are most susceptible to oxida-

tive changes during storage. Investigations have

also found that pressure-cooking chicken breast at

0.36 kg cm

2

produce higher TBA values than

cooking at atmospheric pressure.

0036Smoking is generally advantageous due to the anti-

oxidant properties of the smoke. It has been suggested

that wood smoke may not only aid frozen storage,

due to its antioxidant properties, but also mask off-

flavors. Smoked broilers have been found to keep well

for over a year without any major quality change.

Smoked ham has also been found to store well for a

year at 18



C without any loss of flavor or weight.

0037Studies on chicken breast and salmon have shown

that fast and slow freezing, at undefined rates, have

no effect on the rate of development of lipid oxidation

during storage, slightly higher levels being found in

the fast frozen muscle. In studies on buffalo meat,

plate-frozen meat was scored higher for color, tex-

ture, and overall quality than blast-frozen samples.

Tests were carried out after 3 months’ storage at

15



C, and the freezing times, for 500- to 600-g

pieces, from 4 to 30



C were 280 and 140 min,

respectively, for the plate- and blast-freezing oper-

ations. After 1 month’s storage, the TBA values in

plate frozen cuts were significantly higher than in

those blast-frozen, but the difference had disappeared

after 3 months.

0038Few would disagree that storage temperature influ-

ences frozen storage life and that, in general, the

lower the temperature, the longer the PSL. However,

there appear to be few papers with data from experi-

ments on the PSL of food at different storage

temperatures. Most of the studies published to date

concern products that do not meet the lower-

temperature longer-storage rule (normal stability).

0039It has been shown that rancidity in bacon is in-

creased by a higher salt content and that the rates of

chemical reactions are accelerated as the temperature

is lowered when packed in permeable wrapping.

0.2

0.4

0.6

0.8

1.2

1.4

1.6

0 75 150

Storage time (d)

mg malonaldehyde/kg

Beef LD

Beef SM

Pork LD

Pork SM

Chicken B

Chicken T

fig0001 Figure 1 Raw meat TBA values during storage at 20



C. From Rhee KS, Anderson LM, and Sams AR (1996) Lipid oxidation of beef,

chicken and pork. Journal of Food Science 61: 8–12 with permission.

FREEZING/Structural and Flavor (Flavour) Changes 2739

Studies have shown that free fatty acids accumulate

Further Reading

Anon. (2001) Rapid Cooling – Above and Below Zero.

Paris: International Institute of Refrigeration.

Anon. (1986) Recommendations for the Processing and

Handling of Frozen Foods, 3rd edn. Paris: International

Institute of Refrigeration.

Bald WB (ed.) (1991) Food Freezing: Today and Tomorrow.

London: Springer-Verlag.

George RM (1993) Freezing processes used in the food

industry. Trends in Food Science & Technology 4:

134–138.

Heap RD and Mansfield JE. The use of total loss refriger-

ants in transport of foodstuffs. Australian Refrigeration,

Air Conditioning and Heating 37(2): 23–26.

Kennedy CJ (ed.) (2000) Managing Frozen Foods. Cam-

bridge, UK: Woodhead.

Mallett CP (ed.) (1993) Frozen Food Technology. London:

Blackie Academic & Professional.

Nutritional Value of Frozen

Foods

J S Pai, University of Mumbai, Mumbai, India

Background

0001Freezing of foods has been practiced for a long time,

and frozen foods have become very common today.

All types of frozen foods are available on the market,

from butter, meat, fish, and poultry to semiprocessed

foods like frozen vegetables, orange juice concen-

trate, frozen cake and biscuit dough, French fries,

ready-to-eat processed foods like icecream, and

some items that simply need to be heated in the

oven and are ready to eat. Several decades ago, the

frozen food market consisted of only a few vege-

tables. In recent years, the range and quantity of

frozen food have increased tremendously. Some

2740 FREEZING/Nutritional Value of Frozen Foods

cooked dishes and meals are also being offered in

frozen form.

0002 Freezing has improved the convenience in the prep-

aration of foods. Foods are available out of season

and have a very similar quality to that of fresh foods.

Frozen foods have been evaluated by experts who

observed that when properly prepared and stored,

frozen foods have a nutritional value not only as

good as the fresh commodity but at times even higher

than the commodity procured from the fresh food

market and cooked at homes.

0003 Freezing is used as a method of preservation, since

most microorganisms do not grow at temperatures

below 0



C. Spoilage-causing microorganisms nor-

mally grow on foods and cause spoilage at ambient

temperatures. When the foods are chilled to below



C, the growth of most spoilage organisms slows

down but does not stop. Enzymes present in foods

and microbial enzymes also bring about changes,

resulting in spoilage. These enzymes prefer milder

temperatures. Their activity is reduced when the tem-

perature is lowered. However, chilling temperatures

above 0



C may allow various microbial and enzymic

activities to continue. There are many microorgan-

isms, called ‘psychrophiles’, that grow quite rapidly

at temperatures around 0



C. Thus, although they

have a longer shelf-life than fresh foods, chilled

foods are more perishable than frozen foods. Whereas

chilled foods may last for a few days to a couple of

weeks, frozen foods that are frozen and stored prop-

erly may have a shelf-life of a few months to even a

couple of years.

0004 The spoilage organisms can be destroyed or

stopped from growing and spoiling foods by different

methods, including pasteurization, canning, low-

temperature storage, including chilling and freezing,

chemical preservatives, etc. Heating is the oldest

method, but as well as killing the spoilage organisms,

heat also degrades the components responsible for

color, flavor, texture, etc., affecting sensory proper-

ties. It also destroys many nutrients. Chemical preser-

vatives are undesirable, as people prefer natural,

additive-free foods. Some preservatives have caused

undesirable side-effects in some sensitive individuals.

Drying removes the water from foods, and microbes

and enzymes need water for their activity. Dried food

after rehydration does not completely regain all its

original sensory qualities, and there is also a signifi-

cant loss of nutrients. Chilling and freezing have

therefore gained acceptance with consumers as the

preferred method of food preservation.

0005 Although chilled and frozen foods may not spoil,

their sensory quality and nutritive value may not

remain unchanged. Some nutrients are degraded

during the processing itself. Losses depend on the

process design and rate of freezing. Some nutrients

are lost during frozen storage, and here, also, the

rate and amount of loss depend on the conditions

of storage, including the storage temperature, pack-

aging, type of food being stored, and its composi-

tion, etc. Same factors also affect the color, flavor,

appearance, texture, etc.

Process of Freezing

0006Food is at ambient temperature when it is harvested

and may undergo deteriorative changes unless it is

chilled as soon as possible. If a food is to be stored

unprocessed for long periods, it is normally cooled.

Pretreatments such as washing, cutting, trimming,

sorting, peeling, removal of pit, feathers, skin,

bones, etc., removal of certain parts, and blanching

are carried out prior to freezing. Washing, trimming,

and peeling remove dirt and foreign material and

reduce the microbial load. Blanching is a process

of heating in water or steam and achieves several

objectives in different products. It fixes color in

green vegetables, wilts leafy vegetables like spinach,

so it can be packed tightly into cartons, and removes

undesirable odors associated with some vegetables

and fruits. It also deactivates enzymes naturally pre-

sent in many foods, which, if not removed, cause odor

formation during storage, and it removes dissolved

gases from food tissues. Finally, it reduces the micro-

bial load, and in the case of certain harmful patho-

genic organisms, it might be the only way to control

such organisms.

0007These processes affect the nutrient contents as

washing leaches out some water-soluble nutrients,

and cutting, trimming, peeling, and pitting, etc.

remove parts of the foods that may contain some

nutrients. Blanching not only degrades some tempera-

ture-sensitive nutrients but also leaches out water-

soluble nutrients if hot water is used. Blanching also

disrupts the cells and tissues, so the mixing of differ-

ent components of foods takes place. Some of these

components react and degrade each other.

Freezing Damage

0008The freezing process also causes changes in the tissues

of food of animal and plant origin. Some irreversible

changes are brought about as a result of freezing,

so even after thawing, some changes in the food are

evident. When certain commodities, especially those

of tropical origin, are chilled, changes take place in

membrane lipids and in the structure of proteins. This

affects the integrity of the cells, and nutrient loss

results from mixing with degrading enzymes or

other chemicals.

FREEZING/Nutritional Value of Frozen Foods 2741

0009 When food is frozen, the water in both intra-

cellular and extracellular solutions forms ice crystals,

increasing the solute concentration and affecting

many nutrients. Proteins become denatured as a

result of the loss of water from the protein structures

as well as the increase in solute concentration. Some

vitamins become degraded, as a result of the change

in pH and the increase in concentration of degrading

chemicals.

0010 Ice crystals can cause mechanical damage by

causing excessive stress. Water freezes first from the

extracellular area, and ice crystals start forming there,

increasing the osmotic pressure outside the cells. This

causes the water from inside the cells to move outside,

leading to cellular collapse. The loss of cellular integ-

rity not only allows various chemicals to mix and

react with each other resulting in degradation of nu-

trients, but also causes leakage of watery solution as

drip loss or exudates when frozen food is thawed.

This may lead to further nutrient loss. (See Freezing:

Principles.)

Food Preservation and Nutritive Value

0011 People believe that foods purchased raw and cooked

at home are more nutritious than foods prepared in

factories. It is generally considered that the housewife

or cook at home has a greater expertise and that foods

cooked at home are nutritionally superior to factory

products, as large-scale cooking may not preserve the

nutrients adequately. Although this was probably

true about a century ago, today, factory processes

can be designed scientifically to preserve nutrients

and taste by controlling the processes involved. This

is possible because of the advances in scientific knowl-

edge about foods and the better design of the equip-

ment used for processing. The degree of nutrient loss

depends on the process used: freezing is by for the

least damaging process. (See Preservation of Food.)

0012 Foods are preserved to feed large populations,

especially in urban areas, as well as to make foods

available out of season. Traditional preservation pro-

cesses have included sun drying, smoking, and

salting. Later, other processes such as canning, pas-

teurization, sterilization, and, more recently, chilling,

freezing, and freeze-drying were introduced. In the

ancient times, knowledge of nutrition was limited

and also the motivation of profit overrode concerns

for public health. However, gradually, the knowledge

of nutrients has evolved, and several food laws have

been introduced to ensure the safety and high nutri-

tive value of food. Factory food processed by food

technologists today using newer techniques and more

efficient processes, is highly nutritious and sometimes

even superior to home-cooked food.

0013Raw food is often associated with freshness. It

looks fresh, but it may not have been harvested re-

cently and may have been stored at ambient tempera-

ture for several hours or days. This is called ‘market

fresh’, as opposed to ‘garden fresh’, which means that

a food has been harvested recently. After harvest,

when a food has been kept at room temperature

(which sometimes may be up to 40–50



C in the

summer), there are many changes to nutritive values,

including vitamin contents. Many nutrients like

vitamin C and folate are degraded quite rapidly in a

matter of hours or days after harvest. Green leafy

vegetables in warm climates lose 5–18% of their vita-

min C 2 h after harvest and as much as 90% within

24 h. Garden peas can lose 7% of their total vitamin

C each day, so after a week, they may lose up to 50%

vitamin C.

0014Processing plants, however, have access to freshly

harvested foods, and within hours of harvest, they

may either process them or precool them and store

them until processing, resulting in less nutrient

loss. Thus, processed foods may have a higher

nutrient content in the raw material than those in

fresh food markets. Even after cooking, processed

food may often be more nutritious than market

fresh food cooked at home, particularly with frozen

foods.

0015There are several different mechanisms of nutrient

loss during food processing. Nutrient losses can be due

to physical separation, as in peeling, trimming, etc.,

leaching during blanching, or chemical degradation.

When water is involved in the process, water-soluble

nutrients like vitamin C, folate, B vitamins, etc. and,

to lesser extent, soluble carbohydrates, proteins,

and mineral are lost because of leaching. Boiling or

steeping in water is an example. Heat damages nutri-

ents that are sensitive to higher temperatures like

thiamin, carotene, vitamin A, and vitamin C. How-

ever, when food processing includes heat treatment,

the food is partly or completely cooked, so it does not

have to be cooked again, and brief heating to warm it

is enough. Thus, the loss of nutrients incurred in the

factory is instead of, and not in addition to, that

incurred at home.

Nutritive Value of Frozen Fruits and

Vegetables

0016Fruits and vegetables are important dietary sources of

vitamin C, folate, minerals, carotenoids, and antho-

cyanins, especially in colored fruits, but poor sources

of B vitamins and macronutrients. Some years ago, a

study was undertaken to evaluate frozen foods from

150 factories with respect to vitamins and minerals.

The vitamin contents are listed in Table 1.

2742 FREEZING/Nutritional Value of Frozen Foods

0017 The ranges are quite wide, and, besides experimen-

tal error, this may be because original nutrient con-

tents vary in fruits and vegetable owing to varietal

differences and cultivation and harvest practices. The

freezing process includes precooling, washing and

other pretreatments, blanching and cooling, freezing,

and frozen storage with respect to temperature and

time. All these parameters affect the nutrient con-

tents.

0018 Prefeezing storage at warm or ambient conditions

causes substantial losses. Raspberries left to stand at

ambient temperatures for 24–48 h prior to freezing

have been shown to lose 17 and 30% of their vitamin

C. Strawberries stored at 0



C or lower for 2–4days

showed only slight losses in vitamin C.

0019 Freezing itself has very little effect on nutrients,

but most studies have indicated losses during blanch-

ing and cooling prior to freezing, during frozen stor-

age, and during thawing. Blanching is carried out

before freezing to deactivate the enzymes that might

be active and cause deteriorative changes in nutrients

and sensory quality. Blanching may be carried out in

hot water or steam or by using microwave heating.

0020 The losses include water-soluble nutrients such as

vitamins C, B complex, and folate, and much less

important losses of minerals and a small fraction of

proteins and carbohydrates have been reported.

Figure 1 shows the losses occurring mostly during

blanching and very little during freezing. Not only

does water leach out the vitamins, but heat during

the blanching causes losses of vitamin C and thiamin,

which are heat-sensitive. The type of food, enzyme to

be inactivated, size of pieces, etc. determine the length

of treatment, which in turn affects the vitamin losses.

0021 Losses depend on the area-to-volume ratio of the

material being blanched. Almost half the total vita-

min C is lost from vegetables like peas, sliced beans,

broccoli, spinach, and diced carrots because of the

large surface area-to-volume ratio. Smaller losses of

only about 30% occur in whole beans, potatoes, and

sprouts, which have smaller ratios. Losses are mostly

because of leaching out of water-soluble vitamins.

Microwave blanching does not involve water, so

much less losses are reported. Microwaving is also

more rapid, so heating losses are less. Green beans,

when blanched, lose 9% by microwaving, 14% by

hot water, and 18% by steam. Some studies have

reported almost the same losses by the three methods.

Blanching is followed by cooling before freezing, and

if water is used, the losses are higher compared with

air cooling (see Figure 2).

0022Although blanching causes losses of vitamins,

when vegetables are not blanched, there are greater

losses during frozen storage. Without blanching,

green beans lose 35% and spinach loses 54% vitamin

C during frozen storage at 19



C for 9 months,

whereas blanched vegetables lose only 10 and 24%,

respectively. The vitamin B

and B

losses of

unblanched green beans during 1 year’s storage at

20



C are 74 and 39%, whereas after blanching,

the losses are 22 and 3% only.

0023Nutrient losses in fruits and vegetables are negli-

gible during the freezing process. Studies on various

vegetables like asparagus, green beans, lime beans,

broccoli, sprouts, cauliflower, kale, peas, potatoes,

and spinach have shown that the losses of vitamins

Vit C

(mg)

Vit B

(ug)

Vitamins

Amounts per 100 g

Vit B

(ug)

Fresh After blanching After freezing

fig0001Figure 1 Vitamin losses from green beans.

Spinach

Green peas

Cauliflower

Sprouts

Broccoli

Lima beans

Green beans

Asparagus

Vit B

Vit C

02040

Losses (%)

Vegetables

60 80

fig0002Figure 2 Vitamin losses during blanching.

tbl0001 Table 1 Vitamin contents of some frozen vegetables (mg/100 g)

Frozen vegetable Vitamin Content (approx.)

Asparagus Thiamin 0.10–0.25

Broccoli Carotene 1–3

Brussels sprouts Ascorbic acid 70–110

Lima beans Niacin 1–2

Spinach Ascorbic acid 10–50

FREEZING/Nutritional Value of Frozen Foods 2743

C, B

, niacin, and carotene are either nil or negli-

gible.

0024 Frozen storage, however, causes some losses, and

these are affected by the temperature and packaging

method. Losses at the usual recommended tempera-

ture of 18



C are quite low. More rapid losses have

been reported in vitamin C when frozen peas are

stored at higher temperatures. Other vegetables

show some losses in vitamins C, B

, carotene,

etc. when stored at 18



C, but besides vitamin C,

other vitamins are less sensitive to storage at higher

frozen temperatures (see Figure 3).

0025 Losses of vitamin C from many fruits can be large,

particularly if fruits are not packed in syrup. Rasp-

berries packed in syrup lose only small amounts of

vitamin C. Losses of vitamin C from peaches and

strawberries are generally moderate during frozen

storage, and this depends also on the oxygen barrier

properties of the package. Metal cans are much better

packages in that respect compared with composites

with metal ends. Citrus juice concentrates are reason-

ably stable with respect to vitamin C during frozen

storage for 9–12 months at 18



C. Vitamin C deg-

radation of frozen boysenberries, strawberries, and

peaches is greater when they are stored at higher

temperatures at 12, 7, and 1



C, rather than

18



C. Citrus juices from grapefruit, orange, and

tangerine are more stable at different temperatures.

The stability of citrus juices may be due to their low

pH and low oxygen content.

0026 Thawing conditions have little effect on vitamin

losses, according to the few studies that have been

carried out on vegetables and fruits. Losses of vitamin

C from citrus juice concentrates during thawing are

insignificant. Also, peaches, apricots, nectarines, and

fruit salad packed in syrup lose little vitamin C during

various thawing procedures of different times ranging

from 20 min to 19 h. However, holding the fruits after

thawing at ambient conditions will incur losses of

vitamin C. Raspberries and peaches after thawing

lost up to 15% vitamin in a period from 2 h to 1 day

(see Table 2).

0027Losses of vitamin C in fruits and vegetables during

the entire freezing process have been studied. In some

vegetables, 10–65% of the original vitamin C is lost.

When fruits are protected by syrup and properly

packaged to keep oxygen out, the losses are less, as

in the case of strawberries, apricots, and peaches.

Without sugar syrup, they may lose up to 65–85%,

whereas with syrup and good packaging, their losses

can be reduced to about 15–30% in up to 9 months of

storage at 18



Nutritive Value of Frozen Animal Foods

0028Meat is an important source of many vitamins and

minerals such as vitamins B

, niacin, and iron.

Other vitamins are available, like B

from offals and

vitamin A from liver. There is no blanching in meat

processing, but an important treatment prior to freez-

ing of meat is aging. In one study, beef was aged for

21 days at 1



C, resulting in no loss of thiamin and

riboflavin but a 35% loss of total niacin. Another

study on beef reported no significant losses of vitamin

and pantothenic acid. When pork roast was aged

for 7 days at 1



C, the amounts of thiamin, ribo-

flavin, pantothenic acid, and nicotinic acid were not

affected consistently. Short-term aging with a low

nonfreezing temperature did not destroy vitamins

significantly. Phosphate treatment of fish did not

affect the vitamin and mineral contents, except that

the sodium tripolyphosphate treatment increased the

sodium content by three to seven times that in

untreated samples.

0029B vitamin losses in various animal meat products

such as beef steak, beef liver slices, beef stew, Chicken

la king, Shrimp Newburg, oysters, and pork chops

have been investigated during freezing. No significant

Vit C

Vit B

Carotene

Peas

% Vit losses

Green beans

Spinach

fig0003 Figure 3 Vitamin losses in vegetables stored for 6 months at

18



tbl0002Table 2 Losses of Vitamin C in different frozen vegetables

stored for 6–12 months at 18



Frozen vegetable Vitaminin fresh vegetable

(mg/100 g approx.)

Percent loss after

storage (approx.)

Asparagus 35 10

Green beans 20 45

Lima beans 30 50

Broccoli 110 50

Cauliflower 80 50

Peas 30 45

Spinach 50 65

2744 FREEZING/Nutritional Value of Frozen Foods

losses of thiamin, riboflavin, niacin, pantothenic acid,

and pyridoxine have been reported in these products

(see Table 3). Some losses have been indicated in pork

wherein both freezing and thawing losses were

combined.

0030 Losses have been monitored during frozen storage

of several meat products at 18



C for 6 months.

Losses have been shown mostly in pyridoxine (18–

59%) in beef steak, pork chops and roast, and oysters

with minor losses of niacin and pantothenic acid.

Oyster incurred significant losses of most B complex

vitamins.

0031 Most losses from frozen meats occur when they are

improperly thawed. The amount of drip loss or thaw

exudates depends on several factors such as time

taken to thaw, pH of the meat, state of rigor, ageing

prior to freezing, size of cuts, and freezing rate. The

amount can range from 1 to 10%. The water-soluble

vitamins are lost along with the drip or exudates,

and their retention is better, when meat is thawed at

room temperature or at 0



C, than in warm ovens (see

Table 3).

0032 The effects of various thawing methods have been

investigated. Losses of B vitamins from unpackaged

beef steak are generally greater when water is used for

thawing, rather than air. Thiamin losses are lowest

when a microwave is used for thawing, slightly

greater with infrared heating, and greatest with

boiling with water. In packaged products, the method

of thawing is less significant with respect to losses of

B vitamins. Nutrients lost in thaw exudates have been

estimated for beef and pork (see Figure 4).

0033 The total losses during the entire freezing process

have been evaluated. The meat was aged, frozen,

stored for several months at 18



Cto23



before thawing. The losses are shown in Figure 5.

0034 In a more recent study, when rib steaks were aged

for 5 days, then frozen and stored at 18



C and

thawed at room temperature for 15 h, the losses

were found to be about 10% for each of B

niacin, and folate, whereas about 30% of pantothe-

nate was lost. Almost all of these losses could be

traced to drip losses, and it might be good sense to

include drip or thaw juices with meat before cooking,

so as to recover most of the lost nutrients. There will

of course be a small loss due to heating.

Nutritive Value of Frozen Dairy Products

0035Some products like butter, margarine, and ice creams

are stored frozen. Butter loses only a small amount

of vitamin D when stored at 10



C for 2 years,

whereas butter and margarine lose about 17% of

vitamin A. Ice cream is frozen at lower temperatures.

When frozen and stored at 23



C for 7 months, it

loses 5% of riboflavin, 16% of carotene and all of the

vitamin C (there is very little vitamin C in ice cream

tbl0003 Table 3 Vitamin B

losses from thawing

Frozen food Percent thiamin loss

(approx.)

Beef liver, slices 20

Beef stew 1–10

Chicken a la king 2–10

Shrimp Newburg 4–10

Beef steak

Loss (%)

Pork chops

Thiamin Riboflavin Niacin Pyridoxine

Pantothenic acid Folic acid B

fig0004Figure 4 Losses in thaw exudates.

Oysters

Turkey, leg

Turkey, breast

Poultry, leg

Poultry, breast

Poultry, dark meat

Poultry, light meat

Pork loins

Beef, aged

Beef, unaged

Beef steak, long stored

Beef steak

Beef liver

01020

Loss (%)

Niacin B

30 40 50

fig0005Figure 5 Vitamin losses in the entire process.

FREEZING/Nutritional Value of Frozen Foods 2745

anyway). When frozen milk is stored for 19 weeks at

14



C, the losses in biotin and nicotinic acid are nil.

Comparison of Nutritive Value with Other

Methods

0036 There have been many types of processed foods avail-

able commercially, and there has always been an

interest in evaluating these for the losses of nutrients.

This is a difficult task, as foods have different

varieties as well as degrees of maturity suitable for a

particular method of processing. Thus, if the same

raw material is used for all the processes and unpro-

cessed for control, it would be an unfair comparison.

Also, raw materials of different degrees of maturity

would have different amounts of nutrients, and any

comparisons would be meaningless. Studies have

been undertaken to determine the nutrient losses

resulting from different processes. Green peas have

been processed by different methods and analyzed for

their vitamin C content, the most vulnerable of all the

vitamins (see Table 4).

0037 Cooking losses from fresh food have been com-

pared with those from frozen foods, and the losses

have been shown to be comparable. Many commer-

cial samples have been purchased and cooked and

compared with fresh foods cooked. The amounts of

vitamins B

, and B

show no difference, whereas

some foods such as beef stew, fish cakes, codfish, and

Brussels sprouts show higher values for frozen

samples. Also, the amount of vitamin C is higher in

frozen sprouts. Some experiments have been carried

out with cooked meals that have been stored frozen.

These have been found to have a higher vitamin C

content than conventionally prepared fresh food

meals roughly the some amounts of other vitamins

like B

and B

, and a slightly higher retention of

available lysine.

Frozen Prepared Meals

0038 Frozen prepared meals are either complete meals or

portions of meals that are precooked, packed in trays,

and frozen for retail. Their popularity is due to the

diversity in menu and convenience in preparation.

Typical packs may include meat dishes, vegetables,

pasta products, sauces, and desserts. Meats are often

a major component, which is cooked or fried after

treatments like marinating and tenderization. Heat

treatment removes pathogens and improves the

flavor. While chicken may be completely cooked,

delicate foods like fish are heated for a short time,

allowing the consumer to complete the cooking while

reheating the product. Sometimes, heating may be

carried out after packing meat and applying a

vacuum. Vegetables are either procured frozen, or

raw vegetables are frozen on site after cooking.

Other items are normally prepared fresh and included

in the meal and frozen.

0039Different items are assembled on trays composed of

aluminum foil, paperboard, or plastic. These trays are

embossed to compartmentalize each item. The pack-

age is made so that it can be conveniently reheated in

either an electric oven or a microwave oven. An alter-

native is boil-in-bag meals, which have flexible bags

in which meals are packed, and the frozen packaged is

simply immersed in hot water to heat the contents,

which can be poured on to a plate after cutting open

the bag.

0040Each item may be stored frozen before being added

to the tray, or the freshly prepared items may be

deposited on the tray and then frozen. These products

are fed into the depositing machines, which deposit

them on to the trays, and these filled trays are then

conveyed to the freezer. A belt freezer is commonly

used, in which trays are placed on a wire mesh belt,

which takes the product through a freezing chamber

operated at 40



C. Freezing is accomplished in

a short time, usually about 90 min. Alternatively,

a spiral or plate freezer can be used. After freezing,

the product is packed into cartons and stored at

low temperatures during storage, transport, and

marketing.

0041Freezing per se does not damage nutrients to a

great extent, but the rate of freezing and the different

chemical substances present in the environment of

nutrients may affect the retention of nutrients during

freezing, frozen storage, and reheating. Nutrients are

preserved to a greater extent if individual components

of a meal are frozen optimally and separately and

then assembled on to a tray. However, some or all

of the components are assembled and then frozen

because of the ease of production and economics.

When different items are to be frozen simultaneously,

the ideal conditions are difficult to maintain for each.

Thus, losses may occur to a greater extent. Secondly,

reheating also affects nutrient retention with the

method used (such as oven or microwave heating)

tbl0004 Table 4 Ascorbic acid losses during complete processing by

different methods in green peas

Processof

preservation

Percent loss after

cooking (approx.)

Cooked product

content (mg/100 g)

Dried in air 55 11–12

Canned 60 8–11

Freeze dried 35 13–18

Frozen 40 12–16

Fresh peas 30 16–19

2746 FREEZING/Nutritional Value of Frozen Foods

being an important pronounced factor besides the

storage conditions. The microwave oven leads to

fewer losses, as heating is rapid. Using a higher freezer

temperature leads to greater losses of vitamins such as

vitamin C.

004 2 There are many manufacturers of frozen prepared

meals and many different products available. Al-

though seemingly similar, many have different ingre-

dients and processing procedures. The inherent

differences make it difficult to generalize the nutrient

losses in such products. In one study, it has been

shown that a 300-gram frozen chicken dinner sup-

plies half the RDA of protein, more than 100% of

the RDA of vitamin A, and substantial amounts of

thiamin, riboflavin, vitamin C, niacin, iron, and cal-

cium, whereas a 300-gram beef dinner provides the

following RDAs: 50% protein, 25% P, 60% Fe, 14%

vitamin A, 25% thiamin, 30% riboflavin, and 95%

niacin. A different recipe and processing method

might give different results which will be further

affected by the storage time, temperature, and

reheating procedure. Thus, it is very difficult to state

the nutrient contents of these foods and their losses

during processing and just prior to consumption.

Conclusions

0043 Nutrient losses in the freezing process are primarily

due to blanching in fruits and vegetables, frozen stor-

age in all the frozen foods, and during thawing if

water is used with unpackaged frozen food. These

losses can be minimized if the frozen storage is main-

tained at the recommended temperature of  18



and if the proper packaging method and material is

used to prevent the food coming into contact with

oxygen. Blanching can be carried out without water,

e.g. by using microwave heating. Thawing should be

carried out without contact with water or without

removing the packaging material, preferably at

room or refrigerated temperature. There will be

some drip or thaw exudate losses, which can be re-

duced if the thaw juices are used with the food during

cooking. Modern technology has allowed raw

material of the highest quality to be processed under

ideal conditions, thus incurring minimum losses of

nutrients. Such frozen foods, upon cooking yield

highly nutritious products often containing nutrients

in quantities at least as much as that of home-cooked

unprocessed food.

Seealso: Canning:Principles; Chilled Storage:

Principles; Freeze-drying:TheBasicProcess;Structural

andFlavor(Flavour)Changes; Freezing:Principles;

StorageofFrozenFoods;StructuralandFlavor(Flavour)

Changes; Pasteurization:Principles; Preservation of

Food; Spoilage:ChemicalandEnzymaticSpoilage;

BacterialSpoilage;FungiinFood–AnOverview;Moldsin

Spoilage;YeastsinSpoilage; Sterilization of Foods