Unit 6 - EVALUATION OF FOOD

Introduction

Quality is a desired attribute for any food product.
Consumer choose food on the basis of its quality and their individual likes and dislikes.
When consumer makes a selection they basically look for food that is attractive in terms of colour, flavour, texture, the nutritional quality and shelf  life.
Keeping quality and cost factor are other criteria which may affect their selection .
Today’s consumers are discerning, demanding and more knowledgeable about food.
Therefore knowing consumer’s preferences of the sensory characteristics of food and beverage products is vital to food manufacturers as well as caterers.
Without appropriate evaluation, there is high risk of market failure.

Objectives of Food Evaluation

The major objectives of evaluation of food are:
(1) To develop new products – the food industry depends on evaluation in developing new products and maintaining quality in existing products.
(2) To observe consumer reactions – how the consumer reacts to particular food dictates the quality of the product.
(3) To identify changes in menus to make food acceptable – catering supervisors in institutional food service depend on evaluation to identify changes in menus to make food acceptable.
(4) To collect information of food acceptability –the studies on plate waste provide valuable information regarding food acceptability.
(5) To assist in determining the shelf life of a product.
(6) To understand how the product competes in the market.
(7) To determine whether or not consumers can detect differences between products due to recipe modification.

QUALITY can be evaluated by
(1)sensory methods i.e. by sensory organs like eyes, nose
and mouth
(2)objective methods i.e. by use of instruments.

Sensory Evaluation of Food

When quality of food is assessed by means of human sensory organs the evaluation is said to be SENSORY OR SUBJECTIVE OR ORGANOLEPTIC EVALUATION.
 The method of judging of food is done by a panel of judges.
The evaluation deals with measuring, analyzing, and interpreting the qualities of food as they are perceived by the senses of sight, taste, touch, etc.
By the senses of sight the size shape and colour of the food and other characteristics like transparency, opaqueness, turbidity, dullness or gloss can be perceived.
Other sensory organs i.e. nose and mouth are utilized to obtain information on flavor.
Flavour of a substance is due to the combined senses of taste and a composition sensation known as mouth feel.

The various attributes to be judged are:
APPEARANCE: - The surface characteristics of food product contribute to the appearance
          Example: surface of a chocolate is smooth.

COLOUR – Colour provides variety to the diet and used as an index of quality for a number of foods
          Example: Ripeness of fruits and the strength of tea and coffee.

FLAVOUR – Flavor has 3 components odour, taste, and mouth feel. Mouth feel consists of texture, consistency and temperature of food.
The texture of the food can be smooth or velvety as that of an ice cream or can be coarse as that of corn flakes.

Classification of Methods of Evaluation

Sensory Evaluation

Sensory evaluation is the evaluation of the sensory properties of food (appearance, flavour, texture)
• It can be carried out by the following steps:
Look at the food and describe the overall appearance
Smell the food and describe its aroma
Cut the food and feel its texture
Chew the food and describe the taste and mouthfeel

Sensory properties of food are
Appearance
Involves the sense of sight
Can be described in terms of colour, size, shape, consistency and crumb
• Example: golden brown, small, round, smooth

Texture
• Involves the senses of sight and touch
• Mouthfeel is the sensation when we bite and chew food
•Different cooking methods produce different textures  Example: soft, chewy, crispy, sticky, grainy, coarse etc.

Flavour
• Flavour is produced by a combination of taste and aroma
• Taste – The taste buds on our tongue enable us to detect the different tastes of food – Example: sweet, spicy, bland, buttery, nutty
• Aroma – Involves the sense of smell – Detected by the nose – Example: fragrant, burnt, floral, fishy, fruity

Conducting Sensory Evaluation

A panel of judges is selected. They should be unbiased for tasting.
Physical, psychological and environmental conditions should be maintained as these affect one’s judgement.
The sampling has to be done homogenously.

Preference Test

Judging should be done in individual booths.
This assures independent judgement and communication between panel members should be allowed except for consultation with the panel leader on any point of doubt.
The best time of day for sensory testing is morning 10.00 am to 12 noon and 3 to 5 pm.
The size of the panel is usually 50 to 100 people to avoid any experimental error.
Judgement should be done quickly, but not hurriedly.
They are valuable in developing new foods and in evaluating quality.
These tests are designed to provide information on selected characteristics and to indicate preference or acceptability of products.

Acceptance Preference Test

In this method, a single sample or two samples may be tested.
It is used to find out whether a product will be used by consumers and this also shows their preference for the sample being tested.
If a new food is introduced, only one sample is offered to the panel, but if a food is modified then two samples are offered and their preference is seen.
The HEDONIC SCALE is most commonly used for evaluation.
In this scale ratings of preference or liking and disliking are measured.
It is generally used with untrained assessors.

HEDONIC SCALE
There is also a Facial Hedonic Scale consisting of 5 to 9 faces depicting varying degrees of pleasure and displeasure , it may be used with young children.

Fact Scale

FACT SCALE – food action rating scale

It is a more sensitive method made up of a nine point food action rating scale.
The codes used clearly indicate the action the panelist would take regarding the food i.e. how often the subject would like to eat the food.
FACT Scale

DIFFERNCE TESTING

These tests are designed to determine whether the difference in two or more food products can be detected.
The result of these tests are more precise and reproducible. Tests in this category are:
(1) Discrimination tests
(2) Descriptive tests
Discrimination tests

Paired comparison test 

Prepare two different samples of the food product you wish to test.
Compare one attribute, e.g. which one is smoother?
 Record the response from the tasters.

Duo-trio test

In this test, three samples are to be tested of which two are control samples and one is variable sample.

One of the control sample is presented first followed by the other two sample, and evaluator is requested to identify which of the two sample is different from the control.
The chances of guessing correctly are 50%.

Triangle Test

Prepare three food samples, two of which are the same.
Arrange the samples in a triangle.
Ask the tasters to decide which of the samples is the odd one out.
Record the responses from the tasters
Two Samples A and B can be presented in two combinations AAB and BBA and for replication in six different- AAB,ABA,BAA,BAB,ABB and BBA.

Dilution test

This test is used to measure the quality of an ingredient which has been substituted.
A standard sample is presented to the judges followed by other samples which may or may not contain the unknown at a definite level of dilution.
Example: use of dried egg powder with fresh eggs. If of good quality the product quality will be difficult to get detected, if poor quality the product will be detected at low concentration or high dilution.

Taste threshold test

This test determines the lowest concentration of a substance that can be detected.
It also indicates the lowest concentration of a substance required to be able to identify it.
The taste threshold of sweet, salty, sour, and bitter tastes can be detected.
Sweet - usually indicates energy rich nutrients.
Umami - the taste of amino acids (e.g. meat broth or aged cheese).
Salty – the taste of common salt.
Sour - typically the taste of acids.
Bitter - allows sensing of diverse natural toxins.
Ranking order

 DESCRIPTIVE TESTS

These tests describe the sensory attributes of food in exact words and the judge / evaluator is asked to select the exact word description from the score card which matches with the sample.
These tests are superior to preference tests which provide information about acceptability of a food sample and discrimination tests which detect deviations between samples.
Accurate descriptions of each characteristic of the sample to be evaluated by the judges is described over a range.
The score cards needs to be carefully designed for descriptive testing.
These are two types of descriptive tests.

 Profiling

In this, a panel of experts sit together and formulate a very detailed word description, generally of flavors which is used as a standard for evaluating further product.

Score cards

In this method food samples are individually evaluated by judges with the help of score cards which have a series of descriptive terms or levels of a characteristic.
Numerical values or scores are assigned to each descriptive term.
FOR EXAMPLE : The juiciness of meat which is a textural characteristic is evaluated on the basic of one of the following terms:

Extremely juicy     - 6
Moderately juicy   - 5
Slightly juicy          - 4
Slightly juicy          - 3
Moderately dry     - 2
Extremely dry        - 1

Score cards

While evaluating the food, the judge should think of the appropriate descriptive adjective and take a decision and not decide on the basis of the score.
It is preferable not to mention the numerical score on the score card which is given to the evaluator.
All score cards should have columns to fill the name of the judge and date of evaluation, and this should be filled in advance.

The following are the point to be kept in mind while preparing score cards.

• Select the different characteristics of a food product which need to be evaluated – example – appearance , colour , flavor , texture.
• Select appropriate descriptive terms pertaining to the characteristics chosen and arrange in sequence.
• Give numerical values to the descriptive terms.
• All products which are to be evaluated should be given a code. Codes could be symbols, colours or randomly selected three digit numbers.
• Score cards should be descriptive.

Score cards

Score cards

Environment for conducting sensory test

• Separate sensory booths should be provided so that judges do not interact with each other except when preparing profiles because judges work together to develop vocabulary needed to describe food samples.
• Controlled air and lighting so that food is correctly visible and booth is free from odours other than the sample . Temperature should be comfortable and non-smoking zone observed.
• Small sinks should be provided for spitting out samples or rinsing ones mouth

Sample preparation and presentation

• Samples should be of identical size.
• They should be in identical shape or from identical portions e.g.  edge of cake from one sample and centre slice from another sample should not be taken.
• It should be served at the customary temperature example. e.g.Soup should be served hot.
• Sample plates should be marked.
• Plates or containers used should be of identical size and colour.
• Necessary cutlery, glass of water should be provided at room temperature.
• Only a limited number of samples should be evaluated at a time to avoid fatigue and for efficient judging.

Members of the Panel

• The judge should neither be too hungry or too well fed.
• Smoking, chewing gum or nibbling snacks 20 minutes prior to the test should not be permitted.
• The judges should be healthy and not suffering from a cold as this will affect their sense of taste and smell.

PROXIMATE ANALYSIS

A method for the quantitative analysis of the different macronutrients in food is the proximate analysis
Proximate Analysis is a partitioning of compounds in a food into categories based on the chemical properties of the compounds. The categories are:
moisture
ash
crude protein
crude lipid
digestible carbohydrates &  crude fibre
Purpose of proximate analysis
Estimation and determination of how much of the major food components, which are Moisture, CHO,
Lipids, Proteins, Ash, Crude Fiber, exist in a given food.
It is important to remember that proximate analysis is not a nutrient analysis, rather it is a partitioning of both nutrients and non-nutrients into categories based on common chemical properties.
Purpose of proximate analysis
Moisture Analyses
Crude Fat Analyses
Crude Protein - (Non-protein nitrogen also included) most proteins contain 16% nitrogen. Therefore the general “protein factor” is 100/16=6.25. If we multiply the percent nitrogen by 6.25, we obtain crude protein.
Ash - residue after burning all organic material. Some minerals become volatile at high temperatures of burning and therefore can be lost. Also some minerals occur in the form of salts of organic acids like citrates which contain carbon and are lost.
CHO and Crude Fiber Total carbohydrate = 100 - [moisture + crude fat + crude protein + ash].
Crude fiber: residue left after alkaline and acid digestion of organic matter. If we subtract the total of 1-5 from 100, we get the digestible carbohydrates.

RHEOLOGICAL ASPECTS OF FOOD

It is the science of measuring forces, which are needed to deform food materials or to study the flow properties of liquid foods. It deals with the viscous behaviour of a system.
Solid food can be chopped up, ground, minced, sliced, torn apart or broken while it is being prepared or eaten, the texture is determined as crisp, tough, chewy, creamy, sticky, spongy etc.
Liquid foods are fluid or viscous. Viscosity is defined as the resistance of a liquid to flow. It is measured by an instrument called viscometer. This property of liquid is seen in batters, sauces and syrups.

REOLOGICAL PROPERTIES OF FOOD

ELASTICITY is the tendency of solid materials to return to their original shape after being deformed. Solid objects will deform when forces are applied on them. If the material is elastic, the object will return to its initial shape and size when these forces are removed. Elasticity is a characteristic of importance in baked products such as cake especially when they are fresh. Elastic deformation is reversible.

PLASTICITY- is the tendency of food items to be moulded into shape while soft, and then set into a rigid or slightly elastic form.

VISCOSITY is resistance of a liquid to flow. It is a measure of the resistance of a fluid to deformation under shear stress. It describes a fluid’s internal resistance to flow and maybe thought of as a measure of fluid friction. Thus water is thin having low viscosity while vegetable oil is thick having a high viscosity.

UNIT 5 - FOOD PROCESSING

Introduction

The action of performing a series of mechanical or chemical operations on food in order to change or preserve it.
Food processing takes clean, harvested or slaughtered and butchered components and uses them to produce marketable food products.
Unless natural foods are processed and preserved, they will deteriorate.

Objectives of Food Processing

The main objectives of food processing are:
1.Removal of unwanted matter from the food.
Unwanted matter may be inedible, indigestible or harmful to health. Unwanted matter is removed by appropriately designed gadgets. The processes may include shelling, destoning, milling, peeling etc.

2.Making food safe for consumption.
Some foods contain natural toxins which need to be inactivated. Fungal growth on food items, infected portion of food are removed by visual examination. Heat is used to destroy microorganisms and their toxins.

3. Increasing Digestibility 
Most foods are difficult to digest unless they are cooked. Cooking softens fiber, gelatinizes starch, denatures protein and makes food easier to digest. With exceptions to fruits and some vegetables, all other foods need some kind of processing to make them more digestible.

4. Enhance flavor, colour and taste 
The acceptability of food depends to a large extent on its sensory qualities. Processing techniques enhance the appearance of food and many techniques make food more appetizing and tasteful.

5. Improving texture and consistency 
Processes such as emulsification, aeration, gel formation are aimed at improving the texture and consistency of ready-to-eat, cook-chill and cook-freeze operations.

6. Minimizing nutrient loss 
Nutrients are better retained by controlled processing conditions. Nutrients lost during processing are generally compensated by adding synthetic vitamins.

7. Extending the shelf life 
Processing extends the shelf life because apart from removing unwanted, spoilt and harmful matter and subjecting the food to temperatures outside the danger zone, all processes such as dehydration, cold storage, canning and pasteurization are aimed at preservation of food.

8. Increasing acceptability through fabricated foods 
New products of uniform size and shape are being introduced in the market. They are made from low grade commodities which are plentiful or good for health.

So to summarize,

• Foods are processed for the following reasons:
• All the raw food materials are processed to improve their palatability, nutritional value and shelf-life.
• Preservation for later consumption or sale to fetch better price
• Removal of inedible portions
• Destruction or removal of harmful substances 
• To boost the shelf life of food articles.
• To prevent contamination of food.
• For transportation and food storage.
• To turn food products into the ones that appeal to customers.

Food Spoilage and Contamination

Food can spoil at any stage in its preparation or storage. In fact, spoilage in food begins as soon as

Vegetables and fruits are harvested.
Eggs are laid.
Fish is caught
Animals are slaughtered for meat.
Milk is drawn from milch animals.
This spoilage continues till food is consumed.

Food Contamination: 
The term contaminated is used for those foods which are not fit to be eaten for sanitary reasons. Although contaminated food may look, smell and taste good, it may contain harmful chemicals, non-food matter and bacteria. Contamination of food results in its spoilage.

Food Spoilage:
It is the decomposition or damage causing undesirable changes in food. It is caused due to various agents making food unsuitable for consumption. Spoiled food looks, smells and tastes bad.

Causes of Food Spoilage

Food spoils because of any one or more of the following reasons.

• Growth and activity of bacteria, yeast and mold – Micro-organisms can cause visible changes in the food.
• Insect infestation – Insects such as worms, weevils and moths infest cereal grains and make grains unfit for consumption.
• Enzymatic changes – Natural enzymatic changes also cause food spoilage.
• Chemical action – Rancidity.
• Physical Changes.

Methods of Food Preservation

Use of Low Temperatures

Low temperatures preserve food by retarding chemical reactions, enzymatic action, growth and activity of microorganisms. The lower the temperature , the better the food will be preserved. Microorganisms are not killed at low temperatures.

The various food preservation techniques using low temperature are as follows:

1. Refrigeration / Chilling
2. Cook – Chill
3. Freezing
4. Cook – Freeze
5. Vacuum Packing

Refrigeration / Chilling

Temperature of 1 to 40C prevents food from spoiling for short periods.
Frozen foods kept at -180C preserves food for a year.
Frozen food kept at -280C preserves food for a two years.
Chilling temperatures retard microbial growth and biochemical changes which affect colour, texture, flavor and nutritive value.
Food can be kept at chilling temperatures for a limited period and have to consumed by the ‘best before date’.
Relative humidity needs to be controlled when fruits and vegetables are stored in refrigerators. Low RH means loss of moisture and shrinkage in them and high RH favours surface spoilage by microorganisms.

Cool - Chill
In this system, food is cooked in the kitchen in advance and rapidly chilled and stored at 0 – 30C.
It is reheated just before it is served.
The cook – chill system is used for almost all kinds of foods and is popular in airlines and institutional catering.
Proper cooking procedures and hygienic standards need to be followed to ensure safety and quality.

Precautions for Cook – Chill Foods
Food should be properly cooked to destroy the microorganisms and the cooking process should be complete.
Cooked food should be portioned and chilled in a blast chiller unit within 30 minutes of cooking.
Chilling temperature of 30C must be reached within 11/2 hours after cooking.
Chilled storage temperature should be between 00C to 30C
While distributing cook-chill foods, temperature should be as low as possible.
During reheating the temperature must reach 700C.
Food should be reheated just before it is consumed and must be consumed after 2 hours of reheating.
If the temperature exceeds 100C during storage or distribution the food must be discarded.
Recipes should be suitably modified.
The storage life of cook-chill meals should not exceed 5 days.

Freezing

Food is preserved for long periods by reducing the temperature to -180C or lower.

At this temperature, water gets converted into ice and microbial growth stops.
Freezing retains colour, flavor and nutritive value.
If properly stored, frozen food has a self life of 3 – 12 months.
Food is quickly frozen by using any one of the following equipments.


Blast Freezers – In this cold air at -180C to -340C is vigorously circulated over food while it passes through an insulated tunnel.

Plate Freezers – Food to be frozen is placed in contact with a metal surface which is cooled by a refrigerant. It is used for ice creams, juices, etc., both packaged and unpackaged foods.

Immersion freezers – packaged or unpackaged food is frozen by immersing it or spraying it with a freezing agent. It is used for freezing poultry.

Spray freezers – This is the quickest freezing method in which liquid nitrogen or carbon dioxide is used. It is called cryogenic freezing. The food to be frozen is placed on  conveyor belt which passes through an insulated freezing tunnel. Liquid nitrogen or carbon dioxide is injected into the tunnel through a spray which changes its state and vaporizes, resulting in instant freezing.

Freeze flow – In this system, food freezes but does not harden. A wide variety of frozen foods, both cooked and uncooked are available in the market. A cryoprotectant  is used. Frozen foods once thawed should not be refrozen as when it is thawed its temperature is in the danger zone where bacteria present in the food multiply rapidly.

Cook – Freeze – It is a specialized method of a food processing system in which food is cooked  and immediately blast frozen at -18oC or below and stored at this temperature till it has to be served. It has a shelf life of 3 – 6 months.

Vacuum Cooking

Vacuum cooking is a form of cook – chill using a combination of processes. The food is first sealed in a plastic pouch. It is then cooked by steam and quickly chilled in ice water. 

Although this system has many advantages, its main disadvantages are uneven cooking if size of cut food varies, longer cooking time, and extra cost of vacuum pouches and packing equipments.
Vacuum packed food does not get oxidized and once packed.
Packs must be stored at appropriate storage temperature, well labelled and FIFO must be followed strictly.

Flow of Freezing Process for Fruit Based Products

Flow of Freezing Process for Veg. Based Products

Use of High Temperatures

High temperatures destroy microorganisms by denaturation of cell proteins and inactivation of enzymes needed by them for their metabolism. At temperatures above 630C, bacteria stop multiplying and as the temperature increases, they are gradually destroyed.

The Thermal Death Time (TDT) is the time needed at a given temperature to kill a number of microbes. The heat used to destroy microbes maybe in the form of wet heat or dry heat.

Uses of High Temperatures
WET HEAT

This is more commonly used in the food industry. If carefully administered, it is a useful method of controlling microorganisms. The food processing techniques using wet heat are as follows:

1.Blanching: Foods which are to be frozen, dried or canned are immersed in hot boiling water for a few minutes prior to processing. Balancing helps in removal of peel, inactivation of enzymes that oxidize vitamin C, removal of gas from tissue spaces and wilting of tissues. The enzymes which bring about discoloration or browning seen in apples, pears and potatoes are also inactivated.

2. Pasteurization – This method is used to control microorganisms in milk, fruit juices and wines. Food may be pasteurized by any one of the three methods:
Low temperature holding (LTH) method at 620C for 30 minutes
High temperature short time (HTST) or flash method at 720C for 15 seconds.
Ultra high temperature sterilization (UHTS) at temperatures above 1350C for 2 seconds. This method makes food commercially sterile. Such foods are packed under aseptic conditions and can be stored at room temperature for three to six months.

3. Canning -  In this process, temperatures used are above 1000C. All microorganisms that could spoil food under normal conditions of storage are destroyed by heating the food in an autoclave at temperatures between 1150C and 1250C.

• The exact temperature and time required for canning depends on the type of food to be canned.
• Acidic foods such as fruits are heated to 1000C only because acid also helps in preventing microbial growth.
• A vacuum is created inside the can or the air in the headspace may be replaced by nitrogen gas to prevent growth of aerobic bacteria.
• This is the most common method of food processing . It is used to preserve fruits, vegetables, fish, meat, poultry etc.
• In this process no preservatives are added to the food which is sealed in air tight containers. These are then heated to sterilize the food.

Canning Process

The following basic steps need to be followed while canning or bottling food:

1. Cleaning and Preparing – The food to be canned is cleaned thoroughly and prepared for canning.
2. Filling – Raw prepared food is filled into cans or bottles either mechanically or by hand. Filling should be carefully controlled to ensure that the headspace is neither too little nor too large.
3. Exhausting – A partial vacuum is created in the can by removing part of the air. As oxygen is reduced, bacterial spoilage is retarded. Exhausting prevents the ends of the can from bulging during heating.
4. Sealing – Cans and bottles are sealed with airtight lids by sealing machines.
5. Processing - The sealed containers are heated at a controlled temperature for a specified length of time. The time and temperature depends on the food being processed and the size of the container.
6. Cooling – As soon as processing is over, cans are cooled immediately to stop further cooking. Cans are cooled by dipping them in cold water  or even air cooling. He cans are then labelled and packed in cartoons to be marketed.

Advantages of Wet Heating

1. Convenience
2. Long Shelf life
3. Needs little preparation
4. No chemical preservatives
5. Variety of food is available.

Disadvantages of Wet Heating

1. Heat labile nutrients are lost.
2. Heat required for processing affects the texture, colour and flavor of the product.
3. Cost of canned food is high in India.
4. Once opened, canned food should be treated like fresh food and consumed within stipulated period.

Cooking (boiling, steaming, stewing and poaching)

In these methods of cooking, wet or moist heat is used. The temperature attained is 1000C.
At this temperature, most microorganism are destroyed but spores survive. Foods cooked by these methods cannot be stored for long periods under normal conditions.

Methods of Food preservation

DRY HEAT is used in the following methods.
Sun drying, Smoking and Freeze drying – In these methods, dry heat is used to control microorganisms. Dry heat brings about dehydration of the foods or the surface of the food. It destroys molds, yeast and most bacteria and spores.
Cooking (baking, roasting, grilling) – In these methods of cooking, food is cooked by dry heat. The temperature reached on the surface is approx. 1150C. Most bacteria are destroyed. Internal temperature of food is generally lower.
If food is to be kept for sometime, it should be cooked
thoroughly. Foods cooked by dry heat methods do not spoil as fast
as moist heat methods as they have a lower moisture content.

Removal of moisture from food
Microorganisms need moisture for their growth. If foods are dried or dehydrated (removal of moisture), they will not be spoilt by bacteria, yeast or molds.
Moisture can be removed by sun drying, mechanical dryers and freeze drying.

Sun Drying
It is used for certain fruits and vegetables. The dried items should be turned during drying. Light coloured fruits are sulphured to prevent enzymatic browning. It can be used in hot dry climates only.

Use of mechanical dryers
The food to be dried is passed on conveyor belts through hot air with controlled relative humidity, or hot air is passed through the food. Liquid food such as milk is dried by passing it over heated rollers. Dried food should b packed in airtight containers immediately.

Freeze Drying
In this process, the food to be dried is first frozen in a cabinet. A vacuum is created and by the process of sublimation the ice turns into vapours.
Freeze dried food needs no further refrigeration or preservation. It is light in weight and retains its size and shape , and when soaked in water regains its original size and flavor, It is used to dry fruits, vegetables, meat, poultry and seafood.

Advantages of Drying
Dried food is easy to transport and store.
It has a long shelf life provided it remains dry.
It occupies less storage space.
It is a cheap method of preservation and easy to use.

Effect of Heat, acid and Alkali on Food Constituents

Heat

High temperatures destroy harmful micro-organisms due to coagulation of cellular proteins and inactivation of enzymes required
For the metabolism of these organisms. Heat also causes dehydration which makes water unavailable for microorganisms to survive in.

Acids (Acetic Acid, Citric Acid)
Acids reduce the ph. level of foods below the growth range and also Inhibit metabolic activity.
Effect of Heat, acid and Alkali on Food Constituents

Alkali
 It causes high osmotic pressure causing plasmolysis (breakdown of cell walls) of cells. It dehydrates food by drawing out water and dehydrates microbial Cells.
It ionizes to yield chlorine which is harmful to microorganisms. It reduces solubility of oxygen in the moisture .
It interferes with the activity of proteolysis enzymes

QUESTION BANK

BHM 117 PRINCIPLES OF FOOD SCIENCE (Question Bank)

The questions that follow below carry 10 marks each

1. (a) Define Food Science.

    (b) Enumerate its importance for catering establishments.

2. (a) Classify carbohydrates.

    (b) Describe any five functions of carbohydrates in food preparation.

3. Explain the process of gelatinization with the help of an illustration and state the

factors affecting it.

5. The hotel industry uses the principles of food science in many of its operations.

     Explain how?

6. Food Science is inter-related with various other field. Explain.

7. Name five examples of processed foods available in stores today. What are the

benefits of food processing?

8. Highlight the types of food processing techniques using heat and cold

temperature.

9. (a) Classify carbohydrates.

    (b) Describe any five functions of carbohydrates in food preparation.

10. What are the refining techniques used for oils?

11. Define food science and discuss the relationship of food science with food chemistry, food micro-biology and food processing.

12. What are Fats and Oils? Differentiate between them.

13. Differentiate between amylose and amylopectin. Explain the factors      

affecting starch gel formation.

 14. Define Food Science, Food Processing and Food Microbiology.

      Discuss the inter-relationship between them.

The questions that follow below carry 5 marks each.

Give brief description of the following:

(a)  Dextrinisation

(b)  Gelatinisation

(c)   Commercial uses of fat

(d)  Autoxidation

(e)  Retrogradation

The questions that follow below carry 2.5 marks each.

Answer in brief:

1.    Refining of Fats.

2.    Pasteurization

3.    Winterization

4.    Freezing as a method of Food processing.

5.    Rendering of oil.

6.    Shortening Agent

Fill in the blanks (each blank carries 1 mark)

1.    _________ is a protein present in wheat flour.

2.    The unpleasant odour of fat results in _________.

3.    Flavour reversion is a phenomenon usually encountered in _________.

4.    Rancidity occurs in __________.

5.    The protein gluten is present in __________.

6.    Dry heating of starch is known as __________.

7.    Class of carbohydrate that do not dissolve in water_____________.

8.    A processing technique applying heat which kills only the disease causing micro-organism is ___________.

9.    Starch is present in two forms ____________ and ___________.

10. Frozen foods can be preserved at ____________ degree Celsius for a duration of

one year.

11. Curd is formed due the ________________ bacteria.

12. Undesirable change in flavor and colour of lipids is known as ______________ .

13. _________ is a type of fat extracted from Beef.

14. Rancidity is of two types __________ and _____________ .

15. _____________ is the best thickening agent used in the food industry.

16. The oil extracted by rendering, pressing or solvent extraction is called _________oil.

State whether True or false   (1 mark each)                                                                       (5X1=5)

            (a) Lard is a type of plant fat.

(b)Gelatin is used while making puddings.

(c)Halibut is a type of Marine oil.

(d) Carbohydrates are made up of Carbon, Halogen and Oxygen.

(e) Lipase is a natural antioxidant present in Lipids.

UNIT 4 - PROTEINS

Introduction

Proteins are complex organic compounds that contain carbon, hydrogen, oxygen, nitrogen, and usually Sulphur or phosphorus.
They are composed of one or more chains of amino acids.
Proteins are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies that are necessary for the proper functioning of an organism.
They are essential in the diet of animals for the growth and repair of tissue and can be obtained from foods such as meat, fish, eggs, milk, and legumes.

Basic Structure of a Protein

Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains.
There are 20 different types of amino acids that can be combined to make a protein. 9 are essential and 11 are non essential.
The sequence of amino acids determines each protein’s unique 3-dimensional structure and its specific function.
The bond which unites the two amino acids is called a peptide bond.
 One amino acid has
1 carboxyl group (COOH)
1 amino group or nitrogen group (NH2)
1 hydrogen (H)
And 1 functional group (R)

NH2CHRCOOH.

Classification of protein based on origin

Classification of protein based on characterization

Classification of protein based on function

Structure of Protein

Effect of heat on proteins (Denaturation)

At the molecular level, natural proteins are shaped like coils or springs. When natural proteins are exposed to heat, salt, or acid, they denature—that is, their coils unwind.

When proteins denature, they tend to bond together, or coagulate, and form solid lumps.
Coagulation is what which occurs on the physical structure during denaturation. As the proteins gets denaturated it become a hard or solid structure which is called as coagulation.
An example of this is a cooked egg white, which changes from a transparent fluid to an opaque solid. As proteins coagulate, they lose some of their capacity to hold water, which is why protein-rich foods give off moisture as they cook, even if they are steamed or poached. Denatured proteins are easier to digest than native proteins.

Factors affecting denaturation are

Agents such as acids, alkalis, salts
Increase in temp
 Extensive beating

Effect of heat on proteins (Denaturation)

Effect of heat on proteins (Denaturation)

Stages in heat denaturation

Unfolding of helix of the protein molecules as the cross wise link holding helix is disturbed.
R groups are exposed. Re-bonding takes place between adjacent R groups of protein molecules leading to aggregation of the molecule bringing about increased viscosity. This is the first change in denaturation which is called as surface denaturation.
When sufficient proteins have united, the protein molecules are no longer dispersed as a sol. At this stage protein is said to have coagulated (second stage) i.e. water is held in the capillary spaces formed by the united proteins molecules and the coagulation of protein forms a gel.
If the liquid is separated from the coagulated protein, the protein is said to be precipitated or flocculated i.e. curdling take place (third stage of denaturation)

Effects of Denaturation

Properties of denatured proteins are completely different from their native form.
Denatured proteins are easily attacked by proteolytic enzymes, e.g. cooked meat is more easily digested than raw meat.
They show decreased solubility, e.g. cooked egg white is not soluble in water.
They loss their biological activity as enzymes are destroyed e.g. browning does not take place in boiled potato.
Denatured proteins lose their ability to crystallize.
There is an increase in viscosity of food.
Heat Denaturation results in improved flavour and texture e.g. cooking improves flavour in meat and eggs give structure and improves texture of cakes.
Denaturation of food is irreversible unless it occurs under very mild conditions.

Factors affecting Denaturation

 pH – Denaturation is brought about by controlling pH .
Heat – when egg white is heated at 600 C the protein ovalbumin gets denatured. As temperature increases, coagulation takes place and egg white separates out as a solid.
Surface Denaturation – this is brought about by mechanical means e.g. beating egg white or milk to a foam.  If the foam is heated, as in egg white foam, it becomes firm due to the coagulation of ovalbumin.
Salts – when present in a high concentration, it precipitates proteins out of solution and disperses them e.g. cured ham baked in white sauce.
Moisture – low moisture levels cause less Denaturation than higher moisture levels at the same temperature.

Functional properties of proteins

Gelation 

Gelatin is partially degraded protein prepared from collagen.
 Collagen is the intercellular cementing substance between cells.
Skin, ligaments and bones are hydrolyzed by dilute acid or alkali, breaking collagen molecules into shorter fibrous molecules called gelatin.
Dry gelatin is soaked in cold water for preliminary hydration before adding some hot water. The mixture is stirred to form a sol.
Alternatively, hydrated gelatin is heated in a double boiler for gelatin to dissolve. The concentration gelatin sol is added to gel a liquid stirring thoroughly to prevent from solidifying into rubbery strands or lump.

Foamability 

 Egg white is a viscous sol with proteins dispersed in it. It can be beaten into a foam.
The protein ovomucin, ovogloulin and conalbumin are necessary to form a fine  foam with small air cell. As air is incorporated into the liquid, protein molecule collect at the air-water interface. When more air is incorporated, the water layer gets thinner and protein molecule gets stretched and unwinds from their coiled structure.
Surface Denaturation takes place and makes the foam rigid and when heat is applied protein coagulate forming a permanent foam.

Emulsification

 It is the most important process in the manufacturing of many formulated foods. Emulsion represents a heterogeneous mixture of fat globules. Food emulsions can be of the oil in water (O/W) or water in oil (W/O) type. The difference between O/W and W/O emulsions is that an O/W emulsion commonly exhibits a creamy texture, while a W/O system has greasy textural properties.
Protein emulsifying activity is the ability of the protein to participate in emulsion formation and to stabilize the newly created emulsion. The emulsifying capacity is the ability of the protein solution or suspension to emulsify oil. Emulsifying properties are useful functional characteristics which play an important role in the development of new sources of plant protein products for uses as foods. Proteins are the components that dominate in most food emulsions.

Viscosity 

The viscosity of a solution is related to its resistance to flow under an applied force.
Viscosity or consistency of the products is very important for the consumer acceptance of several liquid and semisolid-type foods (e.g. soups, beverages). High-molecular-weight polymers such as proteins greatly increase viscosity.
The viscosity behavior of proteins is affected by several variables including size, shape, protein-solvent interactions, hydrodynamic volume and flexibility in the hydrated state.

COMMERCIAL USES OF PROTEINS

The major role of protein in food preparation includes the ability of proteins to
Form foams
Bind water and form viscous sols and gels
Get coagulated by heat
Exhibit emulsifying properties
Show enzymatic activity

No single protein shows all these properties and these complex reactions are influences by other constituents present in food. Proteins are of major significance in determining the characteristics and nutritional value of food.
Egg, milk and gelatin are used to make gels, foams, whips, soufflés, meringues, custard, cakes, puddings, confections, soups and sauces.
Protein extract from natural and novel sources are being extensively used in the manufacture of convenience food for catering systems and for low-cost feeding programmes which rely on protein to bridge the protein calorie gap.

COMMERCIAL USES OF PROTEINS

Other commercial uses of protein

TEXTURED VEGETABLE PROTEIN (TVP)

Plant protein can be used to produce textured protein products also called protein analogs. They form an important substitute for expensive animal products. Textured vegetable protein (TVP) includes proteins manufactured from soya bean, ground nuts and other oilseed after oil has been expelled. Proteins can also be extracted from green leaves and certain grass and species of microorganisms such as yeast, mould and bacteria.

TEXTURED VEGETABLE PROTEIN (TVP)

The advantage of using TVP is as follows:

1. They can be used as substitute for real meat in curries, biryanis etc.
2. Alternatively they can be used along with real meat as meat extender by mixing it with meat products as in cutlets, keema matar etc.
3. They are equally nutritious as meat and cheaply priced thereby cutting down the costs
4. They are widely used in the food processing industry.
5. They are acceptable to vegetarians and are used in nutrition feeding programmes.

Test you understanding of Proteins

UNIT - 3 FATS AND OILS

Introduction

• The basic use of fats and oils in cookery is to add richness and flavor to food and as a cooking medium to fry or cook food. They improve the texture of various preparations such as cakes, pastries and biscuits.
• Fats and oils are found in plants, animals and marine foods.
• They are organic compounds composed of C, H and O
• Collectively known as LIPIDS
• Immiscible in water but soluble in organic solvent. (Ether, Chloroform, Benzene and Acetone)
• Unlike carbohydrates – contains small proportion of O and larger proportion of H and C
• Provide more energy per gram than carbohydrates.

Classification based on origin

Classification based on degree of saturation

Difference between Fat and Oils

FAT                                                                             OIL                                                     

Remains solid at room temperature.                                    Remains liquid at room temperature.       
Relatively more saturated.                                                   Relatively unsaturated.
Relatively higher melting point.                                          Low melting point.                                   
More stable.                                                                         Less stable.                   

RANCIDITY

• Development of any undesirable odour and flavor in fats and oils causing spoilage.
• Observed when fats and oils are stored for some time.
• Rancidity develops in fats, oils and the fatty phases of foods such as pickles, fried snacks, cakes, cheese and salad dressings.
• Different fats and oils  show varying degree of resistance to spoilage.
• Vegetable oils deteriorate slow.
• Animal fats deteriorate fast.
• Marine oils having high proportion of unsaturated fatty acids deteriorate most rapidly.

Types of rancidity

HYDROLYTIC – by presence of moisture

OXIDATIVE – by presence of oxygen

HYDROLYTIC RANCIDITY

• Hydrolytic rancidity is brought about by hydrolysis of triglyceride molecule to glycerol and free fatty acids by the  presence of moisture in oils. The rate of hydrolysis is hastened by-
• The presence of enzymes e.g. lipase present in oils which have not been subjected to heat treatment.
• Microorganisms such as molds, yeasts and bacteria present in oils or contaminants during processing.

OXIDATIVE RANCIDITY or AUTO OXIDATION 

• The spontaneous uptake of oxygen by the unsaturated oils exposed to air is known as oxidative rancidity.
• It is the most common and important type of rancidity which results in the production of rancid or tallow flavours.
• Moisture and impurities do not have any effect on oxidative rancidity
• It is a chain reaction.
• Once it begins, it is continuous process.
• Occurs in two stages.

OXIDATIVE RANCIDITY or AUTO OXIDATION 

  First stage
Ø  Induction period fat and oil takes up oxygen from the air.
Ø  Oxygen from the air requires a free radical to combine with the fat.
Ø  Heat light and traces of metal help to form free radicals.
Ø  Free radical is formed to the carbon (by removal of 1 hydrogen molecule) adjacent to the carbon involved in double bond.
Ø  The free radical combines with oxygen (O2) forming a peroxide.
Ø  The new free radical combines with another hydrogen atom of another fatty acid to form hydro peroxide and a new free radical.
Ø  This new free radical again takes up two oxygen atoms.
Ø  The chain reaction continues till all unsaturated fatty acids are used up or all oxygen gets exhausted.
    Second stage 
Ø  The peroxide and hydro-peroxide formed rapidly break down into aldehydes and alcohols
Ø  Break down contributes to the undesirable flavor and odor in rancid fat.

REVERSION

• Many fats undergo a change in flavour before turning rancid.
• This change in flavor is very different  from rancid flavour and is called reversion.
• In rancidity the change in flavour is same for all fats.
• In reversion the flavor may be buttery, beany, grassy, painty and fishy.
• Reversion is seen in fish oils, linseed and soya bean oil.
• For reversion very small amount of oxygen is required as compared to oxidative rancidity.

Difference between rancidity and reversion

Factors leading to rancidity and reversion

Temperature

High storage temperature accelerates the development of odour and flavours in fats and oils.
 Moisture
Presence of moisture in butter and oils brings about hydrolytic rancidity. Clarified butter or Pure ghee does not turn rancid because the moisture is removed by heat.

 Air 
The amount of air in contact with the fat or oil is an important factor in determining its shelf life. Auto-oxidation occurs in the presence of oxygen and reversion occurs with very less amount of oxygen. Potato chips and salted nut turn rancid at a faster rate due to their large surface area.

Light
Light accelerates both reversion and rancidity.

Metals
The presence of metal in traces accelerates the development of both reversion and rancidity as they are active pro-oxidant. Metal contamination can occur from equipment used for extraction and refining of oil.

Degree of unsaturation
This is an important criterion for oxidative rancidity and reversion.
Oils containing high proportions of unsaturated fatty acids and shortening made from such oils show flavour reversion.

Absence of anti-oxidants
The natural presence of antioxidants or addition to oils prevents rancidity. Antioxidant takes up oxygen and gets oxidized thereby preventing rancidity.

Prevention of rancidity

• Store fat at low temperature in a cool, dark place.
• Use airtight container with minimum headspace.
• Keep away from strong smelly foods
• Use steel and aluminum container for storage. Copper and iron containers accelerate rancidity.
• Avoid undue exposure to light and air.
• Addition of anti-oxidants delay the rancidity
• Natural antioxidants present in oil are vitamin E and lecithin.

Synthetic Antioxidants

    I.          BHT – butylated hydroxyl toluene
   II.          BHA – butylated hydroxyl anisole
   III.         TBHQ – tertiary butyl hydroquinone
   IV.         EDTA – ethylene diamine tetra acetic acid
If fats and oils are stored for longer period of time they should be hydrogenated. It increases their shelf life and prevents rancidity

Effect of heat on fats and oils

During cooking or prolonged heating of fats and oils certain changes are seen:

• There is an increase in the free fatty acid content.
• Smoke point is lowered.
• Iodine number decreases.
• Melting point falls.
• Fat turns darker in colour.
• Fats get polymerized.

*The smoke point of an oil or fat is the temperature at which, under specific and defined conditions, an oil begins to produce a continuous bluish smoke that becomes clearly visible.

*All commonly used fats and particularly those high in polyunsaturated fatty acids tend to form larger molecules (known broadly as polymers) when heated under extreme conditions of temperature and time.

Polymerization

• This takes place because of the intense heat which the fat is subjected to during frying.
• Lipid breakdown takes place and free fatty acids are released.
• Fatty acids undergo further changes and form polymers.
• The polymers increase the viscosity of the hot fat.
• The colour darkens and quality deteriorates.
• Gum may be formed at the edge of the vessel.
• It is of utmost importance to avoid unnecessary heating of fats and oils and controlling frying temperature and time.

Care of Fats and Oils

• Fats and oils are used in many preparations and as a method of cooking food. If care is not taken while heating and storing fats, it may result in wastage of food as well as fat used for preparing it.
• Do not overheat fats, as they decompose at high temperature.
• Follow a time and temperature chart for frying food.
• Cover fats when left in the deep fryer and ensure that the temperature does not exceed 90 – 95 0 Celsius.
• Strain fat after use and used fat should be stored in closed containers in the refrigerator.
• When fat has to be reused for frying, replace with equal quantity of fresh fat.
• Do not use fats with a low smoke point for frying.
• To prevent fat from going rancid, it should be stored in an airtight container away from light.
• Fat should be stored in tall containers to keep minimum surface area exposed.
• Copper or rusted containers should not be used for storing fats.

Extraction of Fats and Oils

There are three methods for extraction of fats and oils from animal or vegetable tissues.

• Rendering
• Pressing
• Solvent Extraction

Rendering

This method is mainly used for extracting animal fat from fatty tissues. The tissue from which fat is to be extracted is carefully removed from the carcass and chopped or minced.
Rendering is of two types: Wet rendering and Dry rendering.

Wet Rendering: It is carried out in the presence of water. The chopped tissue is treated with very hot water or steam. Fat melts and forms  a layer on top, which is skimmed off. Fat obtained by this method has a bland flavor and complete extraction is not obtained. Antioxidants are added to prevent rancidity.

Dry Rendering: The chopped tissues are heated without addition of water. Lipids escape from the cells and melted fat is removed by draining and squeezing the fat out of the residue.

Pressing

In this method, oil is extracted by the application of high pressure to oilseeds or fruits rich in oil. The oil obtained is filtered to remove any unwanted matter. Oil obtained from the first pressing is called virgin oil and is particularly bland in taste.

In hot pressing, the oil bearing tissue is rolled, crushed or ground into flakes, and then heated by steam to 70 degree Celsius. The hot tissues are pressed to extract oil. Along with oil, gum and free fatty acids are also extracted.

Solvent Extraction

The crushed or flaked tissue is mixed along with the solvent to extract oil. This method is used to extract the fat remaining in the seedcake after pressing. The solvent is separated from the mixture by evaporation.

Refining of Oil

The oil extracted by rendering, pressing or solvent extraction is called crude oil. It may contain undesirable constituents such as gums, free fatty acids etc.
Crude oil needs several types of treatment to extend its shelf life and make it suitable and pure for use.

Steps in refining oil are as follows:

1.Settling – The crushed solid part is allowed to settle down and is removed by filtration.
2.Degumming and neutralization – The gum and free fatty acids are removed by steam distillation.
3.Bleaching – This step removes undesirable colouring and flavouring contaminants. Oil is filtered through activated charcoal till it becomes light in colour.
4.Steam deodourisation – Steam is injected into the hot oil under pressure to get rid of unwanted odour and then it is cooled rapidly.

Winterization of Oil

• After steam deodorization oils are chilled rapidly without stirring.
• Large filterable crystals are formed.
• These crystals are made of heavy triglycerides with high melting point.
• Separated by filtration and the cold viscous oil obtained is said to be winterized.
• Winterized oils do not solidify in refrigerator.
• Suitable to be used in food which require refrigeration e.g. salad dressings and mayonnaise which can be poured even when chilled.
• Olive oil is not winterized or deodorized as flavor is lost.

Hydrogenation of oil

• Liquid oils can be converted to solid fats by the process known as hydrogenation.
• In this process there is an addition of hydrogen to unsaturated fat thus converting oils into solid fats.
• Hydrogenation takes place in a reactor where hydrogen gas is bubbled through the liquid in the presence of nickel as a catalyst.  
• In this process some of the double bonds between the carbon atoms of the fatty acids portion of the triglyceride molecule are broken and hydrogen is added. This chemical change makes the fatty acid more saturated. The melting points of the fats are thereby increased.
• Hydrogenation increases the stability of oils and prevents it from spoilage due to oxidation which results in rancidity.
• Hydrogenation is utilized in the manufacture of a wide variety of fats such as vanaspati and margarine.
• Sometimes additives such as antioxidants, Vit. A, D are added to the fat.
• Air maybe whipped in, to impart a snow white color.
• Palm oil, palmolein, rice bran, cotton seed, sunflower, maize, soyabean, groundnut, and sesame oils are generally hydrogenated.

Shortenings

A shortening is defined as a fat, solid at room temperature, which can be used to give foods a crumbly and crisp texture such as pastry.  Examples of fat used as “shorteners” include butter, margarine, vegetable oils and lard.

• Oils and fats are used in a baked product to reduce the development of gluten giving the foods a crumbly texture.  The fats and oils break down the gluten into “shorter strands” hence the term shorteners.  Coating the flour in fat prevents the flour from absorbing water hindering the formation of gluten.  If too much gluten developed, the food would be stretchy and elastic.
• Shortening is used in most doughs and batters, to give the baked product a crisp and crumbly texture.   Rubbing the fat in causes the baked product to have a flaky texture, as the dough is separated into layers.  When fat is whisked with sugar, a process called creaming, the texture will be more like a cake, and be soft and springy.
•   Fat that covers the greatest surface area of the flour particle in a particular baked product is said to have the greatest shortening power

Factors affecting shortening power of fats

• Nature of fat – greatest unsaturation have greatest shortening power.
• Concentration – concentration of fat increases, shortening power  also increases.
• Temperature – fats are less plastic and oils are more viscous at low temp.
• Other ingredients – emulsified fat and oils have less shortening power
• Manipulation of fat – proper creaming and stirring of fat increases the shortening power

Popular fats and oils

• Oils – from different oil seeds are available refined or unrefined as a single type of oil or as a blend of two or more oils.
• Butter – available as salted and unsalted.
• Spreads – emulsions of oil and water. Available in various flavours. They are blends of hydrogenated oils, water, milk solids, flavouring and colouring. They are easy to spread as compared to butter and margarine. They provide less calories as the air and water content is more.
• Vanaspati –prepared by hydrogenation of oil.
• Margarine –  a substitute for butter which is fortified with vitamin A & D. 
• Suet – fat around the kidneys of animals.
• Dripping – obtained while roasting meat and used for shallow frying.
• Olive oil – used for salad dressings.
• Fresh cream – obtained by skimming whole milk. Synthetic cream is also available, which is prepared from vegetable oils, water, sugar, soy proteins and added flavor.

Commercial uses of fats and oils

• Fats and oils are used in the food industry because of their ability to
• Increase tenderness and make the product soft.
• Fry or cook food.
• Crispness of biscuits.
• Puff pastry.
• Soft and tender cakes with high volume.
• Get creamed and form foams.
• Impart flavor, colour and aroma to food.
• Softer bread.

Test your understanding of Lipids