2nd Sem | Food Science | Solved Papers | 2015-16

Q.1. Define food science and discuss the relationship of food science with food chemistry, food micro-biology and food processing.

Food Science – Food Science is the systematic study of the nature of food materials and the scientific principles underlying their modification, preservation and spoilage. It is the study of characteristics of foods including chemical, biochemical, physical, physio chemical and biological properties and effect of these on the quality of the product. It also covers application of this information in development of new products and efficient processing techniques.

Relationship with other Sciences

All foods are chemical compounds which undergo various chemical reactions at all stages from production to consumption. These reactions are based on the laws of chemistry. Many processes used while preparing food involve physical changes too. The three states of matter- solid, liquid and gaseous can be observed during food preparation.

FOOD CHEMISTRY

It is the science that deals with the composition, structure and properties of food along with the chemical reactions. It forms a major part of food science and is closely related to food microbiology. The chemical composition of food tells which micro-organism can grow on it and the changes that take place in food because of their growth. Changes can be desirable and undesirable which can lead to contamination of the food and further leads to food poisoning, food infection or just spoiling and thus rendering it unfit for consumption.

FOOD MICROBIOLOGY

Microbiology is the study of micro-organisms. They are very small, usually single celled organisms which are not individually visible to the naked eye. If they are present in large number in food, can lead to food poisoning. They also serve useful role in making of bread and yogurt etc. A knowledge of the factors that flavours or inhibits the growth of micro-organisms is essential to understand the principle of food spoilage and preservation.

Food chemistry and Food microbiology are intimately related to food processing as the processes to which food needs to be subjected to improve its texture, flavour and aroma depends on its composition and ingredients. The time and temperature for food processing depends not only on the chemical composition of food but also on its microbial load and the type of packaging to be used.

FOOD PROCESSING

Food processing is the transformation of cooked ingredients, by physical or chemical means into food, or of food into other forms. Food processing combines raw food ingredients to produce marketable food products that can be easily prepared and served by the consumer. Food processing typically involves activities such as mincing and macerating, liquefaction, emulsification, and cooking (such as boiling, broiling, frying, or grilling); pickling, pasteurization, and many other kinds of preservation; and canning or other packaging.

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Q.2. Define emulsion. Discuss two types of emulsion (O/W, W/O). State the role of emulsifying agent.

An emulsion is a mixture of two or more liquids that are normally immiscible. Emulsions are part of a more general class of two-phase systems of matter called colloids.

S. No.	O/W Emulsion	W/O Emulsion
1.	Dispersion medium is water	Dispersion medium is oil.
2.	Its application can be found in Moisturizing cream.	Its application can be found in butter and cream
3.	In this  water is the continuous phase and the oil is the discontinuous phase	In this the oil is the continuous phase and the water is the discontinuous phase in this case.

Role of Emulsifying agent in food Preparation:

In mayonnaise, the emulsifier is the phospholipids present in egg yolks – they are such successful emulsifiers that as much as 80% oil can be dispersed in the aqueous phase.

Ice cream is another food that would not exist were it not for emulsifiers. It is both a foam and an emulsion, and its texture results from the ice crystals and unfrozen water it contains. But it’s not just creamy products where emulsifiers are crucial – bread and other baked products, where solid particles are dispersed in an airy foam, are enhanced by emulsifiers.

The emulsifiers that are used commercially come from both natural and synthetic sources. They include Lecithins(E322), mixtures of phospholipids such as phosphatidylcholine and phosphatidylethanolamine and are usually extracted from sources such as egg yolk and soybeans. The precise composition of the phospholipids depends on the source. Uses include salad dressings, baked goods and chocolate. Esters or Monoglycerides of Fatty acids(E472a-f) are made from natural fatty acids, glycerol and an organic acid such as acetic, citric, lactic or tartaric. The fatty acids are usually from a vegetable source, though animal fats can be used. Products that use them include ice cream, cakes and crisps. Mono and Diglycerides of Fatty acids(E471) are semi-synthetic emulsifiers made from glycerol and natural fatty acids, which can be from either plant or animal sources. They are used in products like bread, cakes and margarine.

Q.3. What are Fats and Oils? Differentiate between them.

Fats and oils are very important for every human body. It is mainly essential for daily dietary plan. Fats and oils are totally different from each other. In simple terms, fats are animal fats whereas oils are vegetable oils. The other difference is fats tend to be solids at room temperature; on the other hand, oils tend to be liquid at room temperature.

	Fats	Oils
Description	Fats are the fatty acid esters of glycerol and are the primary energy depots of animals.	Oils act to search artery-clogging cholesterol from the bloodstream, carrying it to the liver for processing.
Origin of the word	Middle English, from Old English, past participle of to cram; akin to Old High German  fat	Middle English oil, from Anglo-French, from Latin oleum olive oil, from Greek elaion, from elaia olive
Derived in	12th Century	13th Century
Room temperature	Solid	Liquid
Derived from	Animals	Plants
Types	Trans fat Unsaturated fat Saturated fat Total fat	Monounsaturated fat Polyunsaturated fat
Functions	Degree of saturation Length of fatty acid structure Cis-trans configuration Crystalline structure	Energy reserve Protect vital organs and thermal insulation Transport medium for oil-soluble vitamins Hunger suppressor
	Animal fats – Butter Cream Lard Meats	Vegetable fats – Olive oil Peanut oil Seed oil Corn oil

 

OR Discuss the functional properties of proteins i.e. Viscosity, Foam-ability, Gelation and Emulsification.

FOAMABILITY

Proteins as that present in egg –like ovomucin, ovoglobulin & conalbumin can be beaten into a form. Egg white is a viscous sol with proteins dispersed in it. As air is incorporated into the liquid, the proteins molecules collect   at the air –water interface. When more air is incorporated, the water layer gets thinner and protein molecules get stretched and unwind from their coiled structure.

Surface denaturation takes place exposing the reactive ‘R ‘groups along the protein molecules. These groups unite & give rigidity to the foam. Surface denaturation makes the foam rigid and when heat is applied the proteins coagulate forming a permanent foam

Stages of fresh egg white foam formation

1) Foamy stage 2) Soft peak stage 3) Stiff peak stage 4) Dry stage

• Foamy stage- bubbles are formed on surface, but a bit liquid remains at the bottom of the bowl. Air bubbles are large, opalescent, showing changing colors. Foam is very unstable; mixture is still fluid. Foam at this stage is used for clarifying, emulsifying & thickening of foods. Acid salt & vanilla are added this stage.
• Soft peak stage – As beating whipping is continued more air is beaten into the white, causing a whiter, opaque appearance. Air bubbles becomes more small, all egg white exist as foam slight drainage occur on standing foam is soft and flow slowly. Peaks just bend over. Such foams are suitable for folding into a batter and used for soft meringues or for incorporation with other ingredients in most products.
• Stiff peak stage- Air cells become fine. Foam become stiff & very white. Peaks stand up straight. Stability of foam is excellent, but the foam is not easily folded into other ingredients. Foam at this stage are used for hard meringues, soufflé, omelets.
• Dry peak stage-

When beating is continued beyond stiff peak stage dry foam is produced, it is very white but dull. Breaks into small flakes, not stable. At this stage, the egg white have little utility in food preparation.

GELATION

Gelatin is a partially degraded protein prepared form collagen (commonly used as gelling as agent). Collagen is the intercellular cementing substance between cells. Skin, ligaments and bones (cattle, chicken, pigs & fish) are hydrolyzed by dilute acid or alkali, breaking collagen molecules into shorter fibrous molecules called gelatin. Gelatin contains a large proportion of amino acids which have a great affinity for water. The long thin fibers of gelatin help in forming firm gels at low temperature.

It may be used as a stabilizer, thickener or texturizer in foods such as yogurt, cream cheese and margarine. Used in fat reduced foods to stimulate the mouthfeel of fat and to create volume without adding calories.

VISCOSITY is a resistance to the flow of a liquid. 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.

Emulsification – emulsification The breakdown of fat globules in the duodenum into tiny droplets, which provides a larger surface area on which the enzyme pancreatic lipase can act to digest the fats into fatty acids and glycerol. Emulsification is assisted by the action of the bile salts

Emulsifying properties of proteins basically depend on two effects:

(1) a substantial decrease in the interfacial tension due to the adsorption of the protein at the oil-water interface and

(2) the electrostatic, structural and mechanical energy barrier caused by the interfacial layer that opposes the destabilization processes. The knowledge on the biochemical and physicochemical characteristics, interfacial behaviors and emulsifying properties of proteins will help us understand the structure-function relationship of the emulsifying proteins.

Q.4. Differentiate between amylose and amylopectin. Explain the factors affecting starch gel formation.

Characteristic	Amylose	Amylopectin
Starch structure	Amylose form 20-30% of the starch structure.	Amylopectin forms 70-80% pf starch structure.
Chain structure	Amylose has a linear chain structure.	Amylopectin has a branched chain structure.
Glucose	Amylose has 300-several thousand units of glucose.	Amylopectin has 2000-200,000 units of glucose.
Solubility	Amylose is usually insoluble in water.	Amylopectin is soluble in water
Iodine Test	Amylose gives blue color in iodine test.	Amylopectin gives reddish brown color in iodine test.

 

Factors Affecting starch gel formation-

1)         TYPE OF STARCH

The proportion of amylose & amylopectin in the starch determines whether a gel will form & whether it will be permanent. The straight chains of amylose form bonds quickly & easily while the branches of amylopectin come in the way & prevent formation of firm gel. Starches rich in amylose can form gel at low concentration while starches lack amylose e.g. Waxy starches can form soft gels at high concentration.

E.g. Wheat & rice flours are good thickening agents but poor gelling agents. Chemically modified starches form stable gel.

2)         CONCENTRATION OF STARCH

• Corn starch form a firm gel at 10% concentration while waxy starches lack amylose can for a soft gel at 30% concentration. Starches containing large amts of amylose will gel at low concentration.
  • 1Tbsp sp starch in 1 cup liquid – thin sauce
  • 2 Tbsp sp starch in 1 cup liquid -medium consistency
  • 3 Tbsp sp starch in 1 cup liquid -thick sauce

3)         DURATION OF HEATING

• When starch is heated along with water the hydrogen bonds in the starch granule break and amylose fraction of starch leaches into the surrounding water.
• A starch paste should be heated gradually for granules to swell and release sufficient amylose to form a gel. Prolonged heating results in fragmentation of amylose and formation of a weak gel with pasty texture.

4)         STIRRING

• Vigorous stirring during heating results in fragmentation of amylose.
• A firm gel forms when paste is allowed to cool undisturbed. Amylose starts forming bonds as the mixture cools and starts gelling. Stirring disrupts the bonds and results in a weak gel.
• Essences and colors should be added to the starch mixture as soon as it is removed from heat and not while mixture is cool.

5)         OTHER INGREDIENTS

• Sugar, acids, etc. modify the behavior of starch gel
• The greater the amount of sugar in the product the more delicate the gel is formed, as sugar prevents water from binding to starch
• Acid hydrolyses the amylose chain resulting in a more tender gel. this is seen when acids are added before gelatinization of starch. If added after gelatinization of starch, the gel is soft because of extra liquid from lime juice or fruit juice.

6)         AGING OF GEL

• In a starch gel water is trapped as dispersed phase within the gel. Water is also bonded by hydrogen bonding to amylose molecules and starch granules which form the matrix of the gel.
• When the gel stales or the structure is disrupted by cutting the gel, water which is trapped in the gel is released and gel collapses. This weeping or loss of moisture from a gel is called SYNERESIS

 

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Q.5. Define Enzymatic Browning in food. How will you prevent enzymatic browning reactions?

Enzymatic Browning

The colour change that takes place in fruits & vegetables, etc due to the presence of enzymes is called as enzymatic browning.

• Light colour Fruits and vegetables darken when exposed to air as a result of the presence of oxidative enzymes.
• Enzymatic browning occurs in those fruits and vegetables when the cellular organization is disrupted by cutting, bruising or other injuries to the tissues.
• This is due to the action of oxidative enzymes on the presence of phenolic substances present in the fruit and vegetable tissues.
• Apples, Banana, Pears, Brinjals and potatoes undergo enzymatic browning.
• Enzymatic browning takes place only in fruits and vegetables which contain phenolic compounds. These phenolic compounds act as the substrate, and in the presence of oxygen and by the action of enzymes, the following oxidative reaction is observed:

Some Prevention for Enzymatic Browning Reactions –

By inactivating enzymes: Enzymes can be inactivated by any of the following measures.

1. Application of heat: Blanching or cooking fruits and vegetables which are prone to browning prevents discolouration. Enzymes are protein in nature and heat denatures proteins thereby inactivating the enzymes.
2. Addition of salt: Vegetables may be immersed in a solution of sodium chloride (NaCl) to retard enzymatic browning. The chloride ion of NaCl retards the reaction but this is a temporary measure as it would make food unpalatable.
3. Lowering the pH: Enzymatic browning is prevented by lowering the pH to 2.5-2.7 by addition of acid. Acids used to prevent browning are- Ascorbic acid, Malic acid, Citric acid and lime juice. Ascorbic acid or Vitamin C acts as an antioxidant and retards enzymatic browning.
4. Chilling of food below temperature optimum for enzymatic activity. The optimum temperature for enzymes to act is 43°C.In cold storage, the browning reactions slow down.

By avoiding contact with oxygen, Oxygen should not come in contact with the substrate. This can be achieved by following:

1. Coating fruit with sugar or covering it with syrup keeps atmospheric oxygen away from the surface.
2. Immersing vegetables in water Contact with atmospheric O₂ can be avoided by immersing cut vegetables in water. Since water contains dissolved oxygen, it is more effective if it is first boiled to remove dissolved air.
3. Vacuum packaging It prevents the food from coming in contact with oxygen and thus prevents enzymatic browning

Sulphuring of fruits prior to dehydration

Sulphur prevents oxidative browning due to enzyme activity. Fruit is treated with sulphur fumes prior to drying. Treatment with SO₂ gas or sulphurous acid solution or 0.25% sodium sulfite for 45 seconds prevents browning. Bisulphites & metabisulfites are also used. Sulphurous acid is a strong reducing agent and prevents discolouration.

Q.6. Give brief description of the following:

(a) Dextrinisation

Dextrinisation is the process involving the browning of starch foods when subjected to dry heat. It is defined as the breakdown of starch into dextrin’s (disaccharides.)

Dextrinization (dry roasting of starch)

• When starch is heated without any water, the temp rises rapidly beyond 100ºC.
• Water which is naturally present in flour and high temp brings about chemical changes or degradation of flour, splitting the starch molecule at one or more of the α1, 4 glucosidic linkages. This reaction is called dextrinization and the short chain starch molecules of varying length formed are called dextrins.
• This process is seen when flour is browned while making brown roux for gravies and sauces. Browned flour has lesser thickening ability because of formation of short chain dextrins.

(b) Gelatinisation – Gelatinization (wet heat)

Gelatinization occurs when starch granules are heated in a liquid. It is responsible for the thickening of food systems. The process is an important physic-chemical change associated with the cooking of starchy materials.

When the liquid is heated, the hydrogen bonds holding the starch together weaken, allowing water to penetrate the starch molecules, causing them to swell until their peak thickness is reached.

During the gelatinization, water will be absorbed into the individual starch granules and held there tightly, actually becoming bound water. Bound water is no longer able to flow; the water that is bound in the granules causes granule themselves to swell significantly.

The gelatinizes starch mixtures are opaque and fragile and the ordered crystalline structure of starch is lost.

Gelatinization takes place over a temperature range that varies according to the source of starch and its amylose/amylopectin ratio.

The most important factors that affect the gelatinization temperature are:

• Type of starch
• Amount of tenderizer: sweeteners and fats
• Amount of acid

Q.7. Explain the sensory evaluation of food quality.

Sensory evaluation is an invaluable tool for Quality Control as well as Research and Development. Customers perceive product quality with their senses, and as a result, organoleptic evaluations are an essential component of any Quality Control evaluations.

The aim of the sensory testing is to describe the product. Distinguishing two or more products: are there any differences between the quality, its magnitude and direction.

• 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 info. On flavour
• Flavour of a substance is due to the combined senses of taste and a composition sensation known as mouthfeel.

The various attributes to be judged are-

1. APPEARANCE-The surface characteristics of food product contribute to the appearance. Example: the surface of a chocolate is smooth.
2. 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.
3. FLAVOUR-Flavour has 3 components odour, taste and mouthfeel. Mouthfeel consists of texture, consistency and temperature of food.
4. The texture of the food can be smooth or velvety as that of an ice-cream or can be coarse.
5. Astringency- It is the puckering sensation that is felt on the tongue due to precipitation of certain substances on the tongue.

 

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OR Discuss the types of colloidal system.

 Types of Colloidal System in Food

S.no.	Name of Colloidal system	Dispersed Phase	Continuous Phase	Examples
1.	Sol	Solid	Liquid	Skimmed milk, soups, gravy.
2.	Gel	Liquid	Solid	Curd, jam, jelly, caramel custard.
3.	Emulsion	Liquid	Liquid	Butter, mayonnaise, salad dressing, whole milk.
4.	Foam	Gas	Liquid	Whipped egg white, whipped cream.
5.	Solid Foam	Gas	Solid	Cake, fluffy omelet.

 

• SOL – Colloidal dispersion of a SOLID dispersed in LIQUID.
• GEL – Colloidal dispersion of a LIQUID dispersed in SOLID.
• EMULSION – Colloidal dispersion of LIQUID dispersed in LIQUID.
• FOAM – Colloidal dispersion of GAS dispersed in LIQUID.

Q.8. Explain the following terms (any five):

(a) Pasteurisation – Pasteurization is the process of heat processing a liquid or a food to kill pathogenic bacteria to make the food safe to eat. The use of pasteurization to kill pathogenic bacteria has helped reduce the transmission of diseases, such as typhoid fever, tuberculosis, scarlet fever, polio, and dysentery.

(b) Winterisation – Winterization of oil is a process of removing the higher melting point parts from oil like waxes or triglycerides by slowly cooling vegetable oils and felling saturated glycerides from the solvent. Used primarily for oils in salad dressings. Removing the solid particles is called winterization.

(c) Denaturation of proteins – Denaturation of proteins involves the disruption and possible destruction of both the secondary and tertiary structures. Since denaturation reactions are not strong enough to break the peptide bonds, the primary structure (sequence of amino acids) remains the same after a denaturation process. Protein denaturation occurs when a protein loses its quaternary, tertiary, and secondary structure. Proteins become denatured due to some sort of external stress, such as exposure to acids, bases, inorganic salts, solvents, or heat.

(d) Syneresis – Syneresis is the expulsion (or weeping) of liquid from a gel. It is sometimes a desired result, as in gel filtration. Often it is undesired, such as when the liquid seeps out of pie filling or puddles form on the top of yogurt or margarine

(e) Food rheology –  Rheology is the study of the relation between forces exerted on a material and ensuring deformation as a function of time. In the food industry, rheology provides a scientific basis for subjective measurements such as mouthfeel, spread ability and pour ability.

It is the study of stress and strain or in other words, it is the study of flow and deformation of materials, both solid and liquid under stress and strain condition.

(f) Food enzyme – Enzymes are protein molecules that are present in all living things. They speed up and target chemical reactions, in many cases increasing the rate of reaction millions of times. For example, they aid digestion, metabolise and eliminate waste in humans and animals, and play a crucial role in muscle contraction. Enzymes break down food into compounds for absorption into the bloodstream. After food reaches the small intestine, the enzyme pancreatin further digests protein, carbohydrates and fats in the small intestine

(g) Reaction maillard – it is a protein-sugar interaction. It leads to the development of brown colour in a mixture containing amino acids and reducing sugars. It is also called carbonyl-amine reaction. The brown colour formed contributes to the aroma, flavor, and colour of many ready to eat cereals, baked food, malted barley etc. various factors which affect this reaction are-type of sugar- the more percentage of reducing sugar, the darker the crust in the bakery products, type of amino acid, temperature, moisture.

Maillard reaction also leads to undesirable changes like unfavorable brown colour e.g. In dried milk. Detrimental flavour changes eg. Burnt flavour. Condensation of amino group of protein brown colour+ carbonyl group of sugar

OR Q.9. Explain the classification of food flavours.

Ans – Food Flavours are classified into three major categories: –

1. Natural Flavours

• Herbs- Basil, mint
• Spices- Cardamom, clove, turmeric
• Aromatic Seeds- Aniseed, Cumin
• Fruits- Orange, Lemon
• Vegetables- Pees, Onions, Garlic

1. Processed Flavour

• Caramelized
• Roasted
• Fermented
• Toasted
• Baked

1. Added Flavour

• Natural Extracted Flavour
  • Essential Oil
  • Essence
  • Extracts
• Synthetic Flavour
  • Fruit Flavour
  • Savoury Flavour

Natural Flavours

• They are usually extremely complex mixtures of many different substances. Sometimes the flavour of natural flavouring agent may depend upon a single substance. Eg:- Clove oil flavour is because of chemical eugenol. It contributes 85% of clove oil. ”] 
• Or it may be present in extremely small amounts
• such as citric in oil of lemon which constitutes 5% of the oil.
• Natural flavouring agents are compound of mainly aromatic organic compounds present as volatile essential oils or as non-volatile constituents.  Such as resins and oleoresins. They are formed in the plant during normal plant metabolism and remains as such the plant is harvested.

Processed Flavour

• The flavour that develops during processing by decompositions, the combination with other compounds, or formation of a new compound.
• The following flavours form during processing of various foods.
• Flavour due to enzyme action

Vegetable cuts (onions, garlic) Odour is because of formation of diallyl disulfide.

Added Flavour

• Natural flavour or synthetic flavours are often added to food to increase its acceptability.
• Role of added flavours has gained importance with advancement in technology being used in food industry and development of new products such as bakery and confectionary items, ready to eat foods, beverage and fast food items.

OR What are the objectives of food processing? Describe two food preservation methods.

Main objectives are

• To preserve the nutritive quality of food by preventing them from spoilage due to microbes & other spoilage agents
• Prolong the shelf life (preservation), as processed food is more stable than the raw food.
• Enhance the quality
• Ensure that food is safe for future consumption.
• Ensure availability of many food products throughout the year.
• Ease of storage, transportation and distribution systems.

Two food Preservation Methods

• Use of Preservatives

A preservative is any substance which retards deterioration of food.

1. Class I –natural – Sugar, common salt, glucose, fructose,   vinegar, wood smoke. There is no restriction by law on their addition to food.
2. Class II- chemicals – They are added in defined permitted limits. They are usually added at the end of the processing operation. Eg – benzoic acid, nitrates, nitrites etc.

• Radiation
  • Radiation of various frequencies ranging from low-frequency microwaves to high-frequency gamma rays are used to preserve various foods.
  • Ultraviolet irradiation- effective in killing bacteria and viruses can be used  for  surface sterilization of food
  • Microwave –heat food by penetrating it

Q.10. Fill in the blanks:

(a) __________is the enzyme responsible for undesirable browning in food (phenol oxidase, amylase, papain).
(b) Cream is an example of __________ (aerosol, emulsion, solid foam).
(c) Masticometer is a device used to measure the __________ of a product (Chewiness, flow, colour).
(d) A processing technique applying heat which kills only the disease causing micro-organism is ___________ (sterilization, pasteurization, drying).
(e) A flavour component in wine which contributes to the mouth feel and colour and breaks down during aging is ___________ (nicotine, caffeine, tannin).

(a) Phenol oxidase is the enzyme responsible for undesirable browning in food.
(b) Cream is an example of emulsion.
(c) Masticometer is a device used to measure the chewiness of a product.
(d) A processing technique applying heat which kills only the disease causing micro-organism is pasteurization.
(e) A flavour component in wine which contributes to the mouth feel and colour and breaks down during aging is tannin.