shotly introduction of food classification..

1. Classification of Food
Submitted To:
Mam Saima Kubabib
Submitted By:
Muhammad Hannan
Semester 2nd
B.Sc. (Hons.) Agriculture (Water
Management)
B.Z.U.

2. Food classification based
on Perishability
 All foods differ with respect to their
keeping qualities. Some commodities like
wheat, rice and maize, stay for long
period without showing obvious signs of
deterioration and spoilage, while fresh
fruits, vegetables, meat, fish and milk will
keep only for a few short period. A
comparison of short life of foods can be
made by keeping them under identical
conditions.

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 Thus, when fresh food commodities are
kept at 220C, beef, fish and poultry will
remain acceptable for one day only,
leafy vegetables for one to 7 days, fruits
for one to 20 days and most root crops
for 7-50 days. Naturally or artificially dries
commodities (seeds, fruits, and dried
smoked fish) can keep for 350 days or
longer.

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 Thus, based on the shelf life, the food
processor classifies all food into three
broad categories:
 Stable
 Semi perishable
 Perishable foods

5. Stable Foods
 Stable foods are those that when stored
under proper conditions will remain
acceptable to the consumer for a long
period, ranging from a minimum of three
months to as long as three years. Foods
included in this category are honey,
sugar, dry cereals (wheat, maize, rice,
barley) and legumes (copies, chickpeas,
mash).

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 Processed food like powder, not fat milk,
breakfast cereals and pasta also fall in
this group.
 The food spoilage agents do not readily
spoil the naturally stable food. It is
interesting to note that in this group the
moisture content is low (usually below
15%) which makes their shelf life stable.

7. Semi-perishable Food
 Foods that are kept fit for human
consumption for a fairly long period with
little care in handling and storage are
classified as semi-perishable. These
usually have a shelf life ranging from a
few weeks to a few months. Included in
this group are fresh commodities as
potatoes, ginger, garlic, onions and
some apple varieties. Commercially
processed foods like fried snacks, some
cheese varieties and ice cream have a
normal shelf life of up to 4 months.

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 The semi-perishable foods are often
subject to spoilage by growth of
undesirable microorganisms especially
some bacteria and moulds. The mode of
deterioration in commercially processed
food is usually by chemical reactions like
rancidity in foods containing fats and oil.
 The moisture content of natural semi-
perishable food ranges between 60-90%.
Potatoes and similar commodities can
keep for a few months if they are stored
under proper conditions of temperature
and humidity.

9. Perishable Food
 Perishable foods have shelf life of a few
hours to a few days under modest
storage conditions. Foods classified in
this category are fresh commodities like
milk, meat, fish, eggs, fruits and
vegetables. Among the processed food,
some types of dairy products
(pasteurized fluid milk, cottage cheese
and fresh cream) and fresh bakery
products (cakes, biscuits, bread and
Chappati).

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 Heated canned foods are treated as
perishable when these are open for
consumption or further preparation.
Storage of such foods at low temperature,
e.g, in the household refrigerator, may
prolong their shelf life. The moisture
content in these foods usually ranges from
80-95%.
 The perishable foods are readily spoiled by
microorganisms, especially bacteria. Such
foods having a very short shelf life require
immediate attention by the processor.
These should be consumed or processed
within the minimum possible time from
harvest.

11. Food classification based
on pH value
 pH value of a food affects the rate of
microbial survivals during short storage,
heating, drying and other forms of
processing. This classification provides
information on:
 The possible spoilage microorganisms
 Food poisoning microorganisms
 The choice of heat processing
temperatures

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 According to this criterion, all foods are
divided into four categories
 High acid foods
 Acid foods
 Medium acid foods
 Low acid foods

13. High acid Foods
 Foods having pH below 3.7 fall in this
category. This group includes more citrus
fruit juices (lemon, lime and grey fruits)
and fermented vegetable products
(pickles). The spoilage organisms usually
associated with them are yeast and
moulds. Boiling water processing is
sufficient to destroy the spoilage agents.
 Acid resistant bacteria sometimes pose
problems in these foods. However, these
organisms have a low heat resistance and
are readily destroyed at pasteurization
temperatures (65-88oC). Food poisoning
organisms do not only thrive in high acid
foods.

14. Acid Foods
 Foods within the pH range of 4.5-3.7 fall
in this class. Included in this group are
guavas, orange, mangoes, pineapples,
apples, tomatoes and most other fruits.
Naturally occurring enzymes and non-
spore forming acid uric bacteria are
usually responsible for their spoilage.
Since these organisms have low heat
resistance, pasteurization treatment is
sufficient to destroy them.

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 Few mesophilic anaerobic spore forming
organisms such as Clostridium
Pasteurianum may also cause spoilage in
acid food. These organisms have relatively
low heat resistance and are easily
destroyed at normal atmospheric
processing temperature of 100oC.
 Proper sanitation of the plant will prevent
contamination by these organisms. Food
poisoning organisms do not usually grow in
acid foods. Those that can grow will not
produce toxins. Hence, like high acid
foods, these are also safe in this respect

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 Sometimes canned tomato juice (an
acid food) is subject to spoilage by
Bacillus thermoacidurans, a spore
forming bacterium, which is responsible
for flat sour spoilage of the product. This
organism enters the canned juice
through contaminated equipment or
ingredients and is related to unsanitary
conditions of the processing plat.

17. Medium Acid Foods
 This group includes foods that fall within
the pH range of 5.0 to 4.5. Examples are
most meat and vegetables mixtures with
tomatoes, tomato soup, sauces and
others whose ingredients produce a
partially acidic product. These foods are
spoiled by the same group of
microorganisms as the low acid food
and are subject to similar heat
processing conditions for preservation.

18. Low Acid Food
 Foods with a pH value of 5.0 and above
are grouped into this category. Most
vegetables (carrots, leafy vegetables,
peas and green beans), maize, meat,
milk, eggs and fish fall in this group. Egg
white of freshly laid egg has a pH of 8.0.

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 The medium and low acid foods are spoiled by
naturally occurring enzymes, mesophilic spore
forming bacteria, thermophilic spore former
and non sporing organisms. Since spores are
very heat resistant and can germinate at the
pH of these foods, hence high temperature
treatment (115-1210C) is required to destroy
these organisms and extend the shelf life of the
food.
 Most food poisoning organisms prefer to grow
in the pH range of medium and low acid foods
(>4.5). Consumption of foods containing such
organisms or toxins can produce food in
toxication or infection. Examples are species
from the genera Clostridium, stephalococcus,
shigella, salmonella and Vibrio.