The document classifies foods based on their perishability into stable, semi-perishable, and perishable categories, emphasizing the conditions required for their storage. Additionally, it categorizes foods based on pH levels into high acid, acid, medium acid, and low acid foods, detailing the associated spoilage microorganisms and methods for preservation. Understanding these classifications aids in effective food storage and safety management.

1. Food Classification Based
on Perishability and PH
MISBAH AJAZ
LECTURER, ZU

3. INTRODUCTION
• Some foods have longer shelf life than others.
• Perishability refers to the quickness with which a food gets
spoilt.
• Foods can be classified into three groups depending on
how long they can be kept without any treatment.

4. Food Classification Based on Perishability
Based on the ease with which foods get spoiled, they can be
classified into the following three categories:
1. Stable or non-perishable foods
2. Semi Perishable Foods
3. Perishable Foods

5. 1. Stable or non-perishable 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 include in the category are honey,
sugar, dry cereals (wheat, maize, rice, barley) and legumes.

6. •NPF will keep for months or years without spoiling unless handled and stored carelessly.
•Examples of such foods are all preserved food products (canned, dried, pickled etc), whole
cereal, pulse and seeds, nuts, fats and oils, honey, sugar, salt, some spices and essence.
• 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. Storage of Non-Perishable Foods
Storage of foods should be done in clean containers with tight fitting lids. Containers can be
made of tin, aluminum, plastic or glass. Clay pots may also used in case of large quantities.
A dry cool and dark area should be chosen for storage of non-perishable foods.

8. 2. Semi Perishable Foods:
Food those remain unspoiled for a fairly long period if
properly handled and stored. Example potatoes, onions etc

9. SPF an be stored for a couple of weeks or even a month or two without any detectable signs of
spoilage.
Temperature and humidity of the environment again affects the shelf stability of such foods.
Proper handling and storage can result in fairly long storage without spoilage.
Examples are all cereal and pulses products like wheat flour, vermicelli, and some fruits and
vegetables like pumpkin, roots, potatoes, onions, garlic etc.

10. Storage of Semi-Perishable Foods
• Processed cereal products develop an off-flavor or are infested by insects very easily if not taken
care.
•They should be sieved and cleaned of all such contamination, exposed to the sun for a few
hours, allowed to cool and then stored in tightly covered bottles or other contains.
•Especially onions and potatoes should be stored in a cool, dry and airy place to prevent them
from developing molds or growing shoots.
•They are best hung up from the ceiling in a wire or plastic-mesh basket, or kept in mesh
containers which permit air circulation.

11. Nuts become rancid and get infested with insects very easily, therefore, they should be bought
in large quantities only when storage space is available.
Fruits like apples, oranges and semi-ripe mangoes do last for a few weeks and should be put in a
basket lined and covered with paper to prevent them from drying up. They need a cool
environment to last long.

12. 3. Perishable Foods:
Foods that spoil readily unless special preservative methods
are used. e.g. milk, eggs, meat, fish, poultry, most fruits and
vegetables.

13. PF can be kept at room temperature for only few hours or 1-2 days before spoiling.
In general, the most perishable foods contain a high level of protein or have moisture and
carbohydrates in them.
Special methods are used to preserve such foods.
These foods keep well under refrigeration at household as well as commercial level.
The rate of spoilage varies with the temperature, moisture and or dryness of the environment.

14. Storage of Perishable Foods
•All other vegetables keep well in a cool place with relatively high humidity in a basket overed
with a damp cloth
•Vegetables must be kept in plastic bags to prevent drying by evaporation, if stored in a
refrigerator.
•Do not wash fruits before storing as they spoil faster.
•Remember not to, refrigerate bananas, pineapples, papayas and avocadoes, as these fruits
undergo undesirable changes in texture and flavor at refrigerator temperature.
•Most other fruits keep well, when refrigerated.

15. • Flesh foods like meat, chicken and fish need to be kept frozen at -60 ◦C in a deep freeze for long
term storage.
• Eggs are best kept in a cool place or in a basket in an airy room.
•Milk in boiled form can be kept at room temperature for 6 to 12 hours during winters. Inside a
refrigerator milk can last 3 to 4 days or even more in a closed container.
• The keeping quality of a vegetable depends upon its nature.
•Leafy vegetables wilt and deteriorate within minutes of buying unless they are kept wrapped in
a damp cloth or inside a plastic bag in the refrigerator wherein they last for more than a day or
two

16. • pH value of 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 temperatires.
Food Classification Based on pH

17. Continued…….
•According to this criterion, all foods are divided into four categories.
 High acid foods
Acid foods
Medium acid foods
Low acid foods.

18. 1. High Acid Foods:
Foods having pH below 3.7 fall in this category. This group includes more citrus
fruits (lemon, lime) and fermented vegetable products (pickles). The spoilage
organisms usually associated with them are molds.
Acid resistant bacteria sometimes pose problems in these foods. However, these
organisms have a low heat resistance and are readily destroyed at temperatures
(65-88 ⁰C).

19. 2. Acid Foods:
Foods within the pH range of 4.5 – 3.7 fall in this class. Include in this group are
guavas, orange, mangoes, pineapples, apples, tomatoes and most other fruits.
Naturally occurring enzymes and non-spore forming acid bacteria are usually
responsible for their spoilage.
Proper sanitation of the plant will prevent contamination by these organisms.
Food poisoning organisms do not usually grow in acid foods. Hence, these are
also safe in this respect.

20. 4. Medium Acid Foods:
This group includes foods that fall within the pH range of 5.0 – 4.5. Examples are most meat and
vegetables mixtures with tomatoes, tomato soup, sauces and others whose ingredients are
produced through a partially acidic product.
These foods are spoiled by the same group of microorganisms as the low acid foods.

21. 4. Low Acid Foods:
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, egg and fish fall in this group.
Egg white of freshly laid egg has a pH of 8.0.

22. The medium and low acid foods are spoiled by naturally occurring enzymes, spore forming
bacteria and non spore forming 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 extent the shelf life of the food.
Most of the 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
infection.

23. Summary

24. THANK YOU