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Techno Science Africana Journal, Volume 3 Number 1, June, 2009
CHANGES IN NUTRIENTS DURING STORAGE AND PROCESSING OF
FOODS - A REVIEW
Dandago, M.A.
Department of Food Science and Technology, Kano University of Science and Technology, Wudil, Kano
State
dandago223@yahoo.com
ABSTRACT
Various changes that occur in nutrients during processing and storage of various food products
were reviewed. Preliminary unit operations such as cleaning, soaking, peeling and dehulling
leads to significant losses of vitamins and mineral contents of food products. Applications of
heat during processing also lead to losses quantitatively and qualitatively and it was noticed that
water soluble vitamins were worst affected. Undesirable reactions in proteins which can lead to
decrease in its biological value may also occur in some foods products. Sugars are affected by
leaching and also take part in browning reactions. Irradiation is not suitable for fatty foods.
Recommendations were made on adopting new/modern processing methods to decrease the
losses. Proper storage conditions especially temperature and humidity controls should be
adhered to strictly at the same time local producers/processors should be educated on
consequences of over processing.
Key words: Nutrients, vitamins, dehulling, peeling, leaching, oxidation.
INTRODUCTION
Food is any substance assimilated into the body
of living organism, which provides energy,
material for growth, body repair, reproduction
and assist in regulation of various processes in
the body (Odeyemi and Duramola, 2000). Food is
like fine China not only is it expensive, but it
must be handled carefully because of its fragile
nature. Food products are susceptible to
spoilage, loss of nutrients, insects and rodents
infestations, and changes in color, flavor and
odor (Hurst, Reynolds, Scheler and Christian,
1993).
Storage is defined as holding goods until
needed for further processing, marketing or
consumption. The expression connotes the
expectation that goods would not just be kept,
but in the most appropriate conditions for
maximum retention of both quality and quantity
(Wajilda, 2008).
The term processing cover an enormous
field of widely different treatments carried out to
render food safe, edible and palatable. The major
methods of preservation all cause some changes
in the nutritional value of food but the loss is not
significant. Nutrients are those substances in
foods which when eaten provide nourishment to
the body. The most sensitive nutrients to change
are vitamin C and to a lesser extent vitamin B1.
Other nutrients are much more stable and very
little is lost in most processes. However, greater
losses can occur due to improper storage of food
under adverse environmental conditions (Hurst et
al., 1993).
Cooking improves the digestibility of
foods, promotes palatability and improves the
keeping quality as well as wholesomeness. The
heat used during processing can be a dry heat
(as in baking) or wet heat (as in steaming). Heat
helps to sterilize the food by killing harmful
bacteria, control undesirable enzymatic reactions
and enhance nutrients availability (Okaka and
Okaka, 2001). Proteins are denatured by heat
where they are made more easily digestable by
proteolytic enzymes and cellulosic cell walls that
can not be broken down by monograstric animals
(e.g. man) are broken down during heating. Heat
also helps to inactivate anti-nutritional factors
such as trypsin inhibitors.
There is significant improvement in
quality and digestibility of carbohydrates after
malting process and anti-nutritional substances
in the grains are leached out. Soaking of cowpea
prior to milling helps to hydrolyze the
indigestible oligosaccharides. Foods are made
more stable for certain period of time after
drying, cold storage, irradiation, addition of
preservatives etc however; despite all the
advantages of food processing and storage there
are adverse effects or changes that occur in the
nutrients during some operations. There is need
to understand these undesirable changes in food
nutrients and take possible measures to over
come them.
Changes in Various Nutrients:
Changes in Vitamins and Minerals during
storage
There is every reason to believe that only
insignificant level of vitamin B is lost during
storage of frozen meats provided the
temperature is low enough and does not
fluctuate. The most susceptible vitamins are B1
and B2. Milk may lose substantial amounts of
vitamins B2. and C within few hours if stored in a
clear bottle in sunlight whereas vitamins A and D
are not affected (Hurst et al., 1993).
The vitamin content of cereals (rice and
wheat) remains relatively stable provided the
moisture content does not increase above 10%.
The vitamin B content of stored bread and break
fast cereals remains stable provided good
storage conditions are used.
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Techno Science Africana Journal, Volume 3 Number 1, June, 2009
Vitamins A and C are regarded as the most
important nutrients in fruits and vegetables but
substantial quantities of both vitamins are lost if
kept at room temperature. Vitamin E which is
highly susceptible to oxidation is found in
substantial amount in nuts. The vitamin can be
preserved by vacuum packaging or freezing the
product in oxygen impermeable film (Hurst et al.,
1993).
According to Hurst et al, (1993) drying
does not cause major losses in vitamins provided
the finished food are adequately protected from
oxygen either by proper packaging or use of anti-
oxidants.
Changes in Vitamins and Minerals during
Processing
Because of their essential nature, the extent of
destruction of vitamins during processing is
often the main criterion by which workers judge
the quality of processed foods (Ihekoronye and
Ngoddy, 1985). But it is often realized that home
cooking generally lead to much greater loss of
vitamins than those encountered in industrial
processing. Generally, the skin of fruits and
vegetables is richer in vitamins than other areas
and also the bran of cereals grains contains the B
vitamins. In tuber crops the surface is usually
higher in vitamins than the cortex and
consequently trimming, peeling, washing etc. of
fruits and vegetables; root and tubers prior
processing result in loss of vitamins and
minerals.
To understand the effect of trimming or
peeling on the nutritional value of foods it is
important to understand the distribution of
vitamins on food materials. Vitamin C for
example is higher in the peels of fruits and
vegetables than in the cortex. Niacin and
Riboflavin are also slightly higher in the peel of
fruits. Fresh citrus fruits show much higher
concentration of Ascorbic acid in the outer peel
and inner white skin than in the fruit pulp or
juice whereas in vegetables, vitamins are
normally higher in leafy portions. In carrots for
example, the peel is much higher in niacin and
carotene than the remaining root. The same is
true of palm fruit and potatoes which show
vitamin higher content in the peel than in the
flesh. There is no doubt that trimming and
peeling of fruits and vegetables reduce the
nutrients content, however boiling the food
material with the intact skin helps to retain these
nutrients (Leriei 1998).
In Nigeria, leafy vegetables and many
fruits are hardly processed and only small
quantities of harvested vegetables are sun dried
locally. Losses may occur with vitamins labile to
heat, light and air (Ihekoronye and Ngoddy,
1985). Blanching is the first step for effective
preservation of some fruits and vegetables and in
many instances, blanching treatment is often
combined with the use of chemicals in order to
produce certain desirable qualities. Loss of
vitamins and minerals during blanching can be
significant and is a function of surface area per
mass of product, degree of maturity of the
product, blanching method, blanching time and
method of cooling after blanching. Nutrients
losses that occur during blanching are caused by
leaching, oxidation of water soluble nutrients
and thermal destruction (Walter, Truond and
Espinel, 1998).
Both vitamin A and Carotene are
unaffected by most cooking methods but small
amounts may be lost during frying. Also about
25% of thiamin is lost when potatoes are boiled,
meat looses about 40% of its thiamine content
when roasted and also when bread is baked
about 25% of the thiamine is destroyed.
According to Ihekoronye and Ngoddy (1985), the
overall loss of water soluble vitamins is greater
than that of fat soluble vitamins during cooking.
Preservation by freezing and storage of these
frozen products is generally regarded as the best
method for long term preservation when judged
on vitamin retention. Losses that occur are
generally not significant if proper packaging and
freezing procedures are used. A loss in the
ranges of 0-40% vitamins does occur in
vegetables and animal tissues during frozen
storage (Okaka and Okaka, 2001).
During flour milling, the outer coat
where B complex vitamins and minerals are
localized are removed in order to obtain flour of
desirable texture (Asiedu, 1989). This
necessitates flour enrichment with vitamins and
minerals after milling.
Changes in Proteins during storage
The biological value of proteins is usually
little affected by proper storage of food products.
High storage temperature will cause certain
amino acids (e.g. lysine) to chemically bind with
simple sugars to form brown pigments through
maillard reaction. The reaction affects the
nutritional value of the food because it causes
the essential amino acid to become
physiologically unavailable (for example
improperly stored dried milk and egg white
powder are particularly susceptible to this
browning reaction) the reaction will also occur if
poor packaging of dried foods allow as increase
in moisture level (Hurst et al., 1993).
Changes in Proteins during Processing
A number of changes may occur during
processing, some of which are desirable while
others are undesirable. Some chemical changes
may lead to compounds which are non
hydrolysable by the intestinal enzymes; or to
improvement of nutritional value by deactivating
certain anti-nutritional factors such as trypsin
inhibitors (Ikeme, 1990). The types of changes in
protein during processing are recognized as
follows:
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Techno Science Africana Journal, Volume 3 Number 1, June, 2009
1. Denuturation which requires mild heat is the
unfolding of the protein complex structure,
and according to Nielsen (2004) the effects
of denuturation include:
(a) Peptide bonds of the protein are more readily
available for hydrolysis by proteolytic
enzymes.
(b) Enzymes activity if originally present is lost
or decreased.
(c) Crystallization of protein is no longer
possible.
(d) Intrinsic viscosity is increased.
Afterall boiling and roasting of food materials
certainly denature the protein as indeed will
the acid of the stomach, but there is no loss
of nutritive value (Behsnilian, Regier and
Stahl, 2003).
2. The second type of change is caused by mild
heat in the presence of reducing substances
which results in a linkage between the end
epilson amino group of lysine with reducing
substances which can not be hydrolyzed by
the digestive enzymes. The lysine is still
present and is liberated by acid hydrolysis,
but since it can not be librated during
digestion, it is biologically unavailable.
3. More severe heating reduces availability of
other amino acids as well as lysine and can
occur in absence of reducing substances. At
temperature of 1150C, cystine is relatively
sensitive and can be oxidized to disulphide
or disulphene. Milk for instance is
pasteurized at 720C for 15 seconds
(Ihekoronye and Ngoddy, 1985). Changes in
temperature and time will lead to off flavor
production because of unfolding of -lacto
globulin. Consequently, there is exposure of
sulphadryl groups of cystine for hydrolysis
and production of hydrogen sulphide. Also
light induced oxidation of proteins is known
to lead to off flavor and destruction of
essential amino acids in milk. Sunlight
attacks methionine and converts it into
methionol which cause a typical sunlight off
flavor at 0.1ppm (Behsnillan et al., 2003).
The source of light induced off flavor in milk
resides in low density lipo protein fraction.
4. Excessive heat such as applied to the outside
of foods of the puffing exploding type of
processing used in the manufacture of some
breakfast cereals and pop corn causes
severe protein damage. It leads to the
destruction of amino acids by complete
decomposition or by forming of cross
linkages forming poly amino acids.
Temperatures of 1800C such as used in
roasting meat, fish, coffee and biscuit baking
have these effects (Ihekoronye and Ngoddy,
1985).
5. Alkali treatment in conjunction with heat
treatment and oxidation damages protein
quality. Alkali treatment is been used in
preparation of protein concentrates and
isolates. This treatment leads to the
formation of new amino acids such as Lysino
– alanine, Lanthronine and ornithino-alanine.
Cystine, lysine and serine are primarily
involved in such reactions (Ihekoronye and
Ngoddy, 1985).
6. Ionizing radiations is a modern method that
is employed in food processing and
preservation. These radiations can produce
charged particles (ions) in the materials they
strike and hence undesirable reactions may
occur. In proteins, deaminations, oxidations,
polymerization and decarboxylation have
been observed during irradiation. Histidine,
phenylanine, Tyrosine and sulphur
containing amino acids are reported to be
the most sensitive to the effect of irradiation
(Fellows, 2000).
Changes in Lipids during Storage
The nutritional value of fat lies in the energy it
supplied to the body during digestion. Fats are
fairly stable to processing (except frying) but may
undergo quality deterioration during prolonged
storage.
Oxidation and hydrolytic rancidity occurs
in stored foods leading to off flavor development.
These reactions can be caused by enzymes or by
moisture and air. They occur more rapidly under
adverse conditions but can also develop in
properly stored fatty acids. Lipids oxidation
produces off flavor components called hydro
peroxides and peroxides which react chemically
with fat soluble vitamins rendering them
nutritionally useless. Loss of these nutrients can
be minimized by wrapping foods in moisture
proof and oxygen impermeable packaging
materials (Hurst et al., 1993).
Changes in Lipids during Processing
Excessive heating will cause reaction of carbonyl
components resulting from the decomposition of
unsaturated fatty acids which may lead to
reactions similar to those involved in non-
enzymatic browning. Lipases and phospholipases
release fatty acids from meat and fish during
frozen storage and free fatty acids are more
susceptible to oxidative rancidity (Okaka and
Okaka, 2001). This problem is especially
important in products with high degree of
unsaturated fatty acids (e.g. pork and sea foods).
Many irradiation promoted reactions
occur in lipids and produce results similar to
oxidative rancidity with loss in fat soluble
vitamins. Several carbonyl compounds may be
formed together with other potentially active
intermediates that can be carcinogenic.
Changes in Carbohydrates during Storage
Carbohydrates can be said to be relatively stable
to processing and storage compared to sensitive
nutrients such as vitamins.
There is no significant loss in the
nutritional value of carbohydrates in frozen,
canned or dried foods.
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Techno Science Africana Journal, Volume 3 Number 1, June, 2009
Infact, some carbohydrates are made more
digestible through processing and thus
nutritionally available and complex
carbohydrates are converted to simple sugars.
Adverse brown pigments occur in frozen and
dried foods when carbohydrates react with
proteins (Hurst et al., 1993).
Changes in Carbohydrates during Processing
During wet heat treatment as in blanching and
boiling; there is considerable loss of low
molecular weight carbohydrates as well as micro-
nutrients into the processing water. The loss of
glucose and fructose at boiling is higher than
that of sucrose. The loss of low molecular weight
carbohydrates also may vary between species and
cultivars.
Non enzymatic browning reactions occur
between reducing sugars and amino groups in
foods during processing and storage. These
reactions are temperature dependent and most
extensive at intermediate water activities (Leriei,
1998). They are important nutritionally as they
may diminish the bio availability of amino acids
especially lysine and thus diminishing the protein
nutritional value. The carbohydrate content and
availability is influenced only marginally.
When starch is heated in the presence of
water, the starch granules ruptures and form
gels. The gelatinization increases the availability
of starch for digestion by amylolytic enzymes.
Gelatinized starch is not in thermodynamic
equilibrium and according to Leriei (1998) there
is therefore a progressive re-association of the
starch molecules upon ageing. This
recrystallization is referred to as retrogradation
and may reduce the digestibility of the starch.
Changes in Moisture during Processing
Changes in moisture content of dried and frozen
food can affect the nutritional quality of food.
Increase in the moisture level of dried food
promotes microbial deterioration and accelerate
rancidity. Improperly wrapped foods suffer form
freezer burn which is a form of dehydration from
the food surface. This loss of moisture causes
oxidation of fats and browning leading to off
flavor development and at the same time
lowering the nutritional value of the food (Hurst
et al., 1993).
CONCLUSION AND RECOMMENDATIONS
Processing foods is necessary to achieve
desirable sensory and healthy attributes in the
food product. Storage of food materials is also
necessary to extend the shelf life of the product
and make it available for future use and for
processing. Because storage and processing of
foods are inevitable, there is need to devise
methods to at least reduce the adverse effects
due to these processes. These effects can be
reduced by the following recommendations:
i. Strictly following the storage conditions of
temperature and relative humidity for the
particular food product and also avoiding
temperature fluctuations.
ii. Adopting high energy transfer processing
method such as (HTST) to reduce the
treatment time.
iii. Adopting new processing methods such as
high hydrostatic pressure technology, ohmic
heating, and ultrasound technologies where
necessary.
iv. Improving temperature, humidity control and
packaging systems in food storage and
distributions
v. It is also recommended that the populace be
educated on the effect of over processing on
the nutrients and suggest possible ways to
avoid it. This can be achieved through radio
jingles and or use of extension workers.
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Behsnilan, D., Regier, M. and Stahl, M. (2003).
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Fellows, P. (2000). Food Processing Technology:
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Hurst, W.C. Reynolds, A.E., Schuler, G.A. and
Christian, J.A (1993). Maintaining Food
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Cooperative Extension Service Bulletin 914.
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