Maharashtra Board Class 11 Food Science and Technology Chapter 7 Food Spoilage PDF Download

Food Spoilage

Most of the natural foods have a limited shelf life. Some foods such as fish, meat, milk, bread, tomatoes, etc have a short life span as they contain high amount of moisture. Other foods are kept for a considerably longer time (low moisture food) but may get decomposed eventually. Once food has been harvested, gathered or slaughtered, it starts to deteriorate until it becomes unfit for consumption. This deterioration is known as decay and leads to food spoilage.

Spoilage is the process in which original nutritional value, texture, flavour, etc. of food are damaged, such food ultimately becomes unacceptable for consumption. Hence, it is essential to process or preserve foods after harvesting or slaughtering to combat the problem of food spoilage.

Definition:

"Food spoilage is the process of change in physical, chemical, microbial and sensory properties of the food so that it becomes unfit for human consumption. Food spoilage is any undesirable change in food and such changes can be detected by smell, taste, touch or sight."

7.1 Classification Of Food On The Basis Of Spoilage

Food commodities can be classified into three groups on the basis of moisture content as perishable foods (high level of moisture), semi-perishable foods (medium level of moisture) and non-perishable foods (low moisture).

1. Perishable Foods

Perishable foods are those likely to spoil, decay or rot quickly so that they become unsafe for consumption unless special preservation methods are used. Perishable commodities usually require some sort of refrigerated storage. Perishable foods include dairy products, eggs, meat, fish, poultry, fruits and vegetables, cooked foods and leftovers.

2. Semi-perishable Foods

Semi-perishable foods are those that do not require refrigeration, having medium level of moisture but still have a limited shelf life. They include foods like potatoes, apples, onions, etc.

3. Non-perishable Foods

Foods that do not spoil under normal storage conditions for a reasonably long time (contain low moisture) are known as non-perishable foods. These foods have long shelf life and don't require refrigeration. These items are usually kept under dry and cool storage conditions and are protected from moisture e.g. grains, flour, sugar, pulses, toast, biscuits, etc.

Teacher's Note

In your home, milk and fish spoil quickly, so we keep them in the fridge. But rice and flour stay fresh for many months without the fridge. This is because milk has more water.

Exam Trick

Remember: Perishable = needs fridge (Meat, Fish). Non-perishable = no fridge needed (Rice, Dal). Just like your phone battery (needs charging) vs a battery in a wall clock (lasts for years).

Points To Remember

Perishable foods have high water and spoil fast.
Semi-perishable foods have medium water and spoil slowly.
Non-perishable foods have low water and last for many months.
Moisture is the main thing that makes food spoil.

7.2 Signs Of Food Spoilage

Food deterioration is manifested by the reduction in aroma, flavour, texture and nutritional values of foods. Different types of undesirable changes may occur due to spoilage in food are listed as follows:

Change in colour: The fruits like banana turn black after storing for a long period of time and reduce the acceptability of food. (black, soft and fermented)

Change in smell: Rancid smell of spoiled oils, fatty food, bitter smell of curd or sour smell of starchy food. (rancid samosa, potato wada, chakali, etc.)

Change in consistency: Curdling of milk, stickiness and undesirable viscosity in spoiled cooked dal, curries and vegetables (thread, foam, bubbles).

Change in texture: Some vegetables like potato, brinjal, carrot, etc. undergo too much softening leading to rotting, changes in firmness. Lump formation take place in powdered materials (milk powder, wheat flour).

Change due to mechanical damage: Mechanical damages such as eggs with broken shells, bruising of fruits and vegetables during harvesting, packaging, transportation and handling, causes damage.

These gradual changes that cause deterioration and decay (rotting) in foods may occur due to certain organisms and chemicals present in the food and outside the food.

Teacher's Note

When banana becomes black or when milk becomes sour, these are signs of spoilage. You can see, smell, and taste these changes easily at home.

Exam Trick

Remember: Five signs are Color, Smell, Taste, Texture, and Mechanical damage. Think of your five senses - you can detect spoilage by seeing, smelling, tasting, and touching the food.

Points To Remember

Color changes show spoilage - banana becomes black.
Bad smell tells us food is spoiled - like sour milk.
Texture changes like soft vegetables mean spoilage.
Broken egg shells allow germs to enter.
All these changes make food unsafe to eat.

7.3 Factors Affecting Food Spoilage

Food spoilage may occurs mainly due to one or more of the following factors:

a. Microorganisms

The microorganisms that can cause food-borne illness are called pathogenic microorganisms. These microorganisms grow best at room temperatures, but most do not grow at refrigerator temperatures. Pathogenic microorganisms may grow in foods without any noticeable change in odour, appearance or taste. When food spoilage microorganisms are present, the food usually looks and/or smells unpleasant. These microorganisms include bacteria, yeasts and molds.

b. Enzymes

Enzymes are proteins in nature and they acts as biocatalyst in chemical reactions. They are responsible for spoilage in fruits and vegetables that causes changes in texture, colour and flavour e.g., softening of banana tissues, browning of cut apple.

c. Air

Oxidation is a chemical process that produces undesirable changes in colour, flavour, texture and nutritional content of food. e.g. rancidity, discoloration of light-colored fruits and loss of vitamine C.

d. Light

Light exposure could result in loss of colour and vitamin. Light also may be responsible for the oxidation of fats.

e. Insects And Rodents

These creatures require food to survive, therefore they damage packed and stored food making it more vulnerable to further deterioration.

f. Physical Damage

Bruises, cuts and cracks on raw produce (fruits and vegetables) may cause due to mishandling where microorganisms can grow easily and leads to spoilage. Dented cans, improper and broken packages provide places for microorganisms, air, light and creatures to enter into it easily.

g. Temperature

At higher temperatures food will get deteriorated at faster rate. Microorganisms, will grow rapidly at room temperature. At this temperature the growth of microorganisms, chemical reactions, biochemical reactions, metabolic reactions (ripening, respiration and transpiration) increases the rate of spoilage.

Do You Know?

Water is an essential component of all foods, even dry foods items like flour also contains water. Water or moisture greatly affects the keeping qualities of food. Moisture can adsorb on the surface of a product and can cause many food defects like moulding, sogginess, caking and lumping of dry products. Water in foods can be controlled by drying, freezing, concentration, packaging, etc.

h. Time

Microorganisms require optimum time and favourable atmosphere to grow and multiply. Under favourable conditions such as temperature, moisture, pH, gas, concentration, microorganisms grow rapidly and thereby cause food spoilage and illness.

Teacher's Note

In your kitchen, if you leave cooked food at room temperature for many hours, germs grow and food spoils. But if you keep it in the fridge, it stays fresh longer because cold stops germs from growing.

Exam Trick

Remember: Temperature, Moisture, Time are the three main factors. If temperature is high, moisture is high, and time is long - germs grow fast and food spoils quickly. It's like watering a plant - more water and more sun = faster growth.

Points To Remember

Bacteria, yeasts, and moulds are living things that spoil food.
Enzymes make fruit soft and apples brown.
Air and light damage food by oxidation.
Insects and rodents eat stored food and make it bad.
Temperature, moisture, and time are key factors for spoilage.

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