Food Science 1st Semester

Definition and scope of food science

Food Science


Food science is the application of basic science and food engineering to study the fundamental physical, chemical and biochemical properties of food and food processing.

Food science was first used to describe the activities involved in moving food from farm to table. This implied the trans formation of raw materials to usable food stuffs, wheat to bread, animals to meat, milk to butter and cheese.

Food science is inevitably drawn into certain aspects of farming on the one hand and into problems of human and animal nutrition on the other. Food science may be applied to develop technological processes designed to produce sophisticated foods to increase the palatability of the consumers. The development of food science and technology that enables foods to be preserved by canning, dehydration and freezing so that they can be produced and processed in those parts of the world best suited to their culture, transported safety half round the world and be made available to distant markets at any season of the year.

Its relationship with food chemistry, food microbiology and food processing:

Food chemistry is the science that studies the composition of the earth and it has been built up mainly from observation and experiment. The rapid growth of the food industry, into big business and the changes in the number of items on the grocer’s shelves, the many ready to eat products, the new control on food additives and the attempts to standardize some food articles, all serve to emphasize the growing importance of the chemistry of foods.

Dependednt os the science of food is on biology, bacteriology and mycology as well as chemistry, it was necessary for all sciences to develop to the point where education (to make clearer) of the complex mixtures encountered in foods become accurate and meaningful. Fortunately research of significance to food chemistry is now appearing not only in journals devoted exclusively to food problems but also in those in the fields of biology, chemistry, engineering and even physics.

The nineteenth century saw the development of ornganic chemistry, analytical chemistry and physical chemistry – all essencitl to thegrowth of food chemistry and our understanding of it. The pace at which discoveries were made and at which advances occurred increased thourghout the century. The field of CHO, began to fit together, proteins mere recognized and many other compounds of importance in food chemistry were studied.

Food Technology: is the used information generated by food science in selection. Processing preservation and utilization of food science affects the consumption of safe nutritions and whole some food. Since food science is a broad conception it contains many other specialization in it such as :

Food Engineering, food Microbiology, food chemistry

Food Engineering deals with the conversion of all raw agricultural ingredients such as wheat to a finished product such as flour or baked goods. It also covers the unit operation mechanism and chemical aspects.

Food Microbiology deals with ecology of food. The role of environment in food spoilage, the presence and nature of micro organisms responsible for food spoilage and the physical, chemical, biological changes brought about by them. Food microbiology also deals with the study of public health and sanitation.

Food chemistry helps in understanding the physical and chemical nature of food  and the changes takes place during processing and storage of food

Food processing deals with the general characteristics of food raw materials, harvesting, assembling and  receiving of raw materials, methods of food preservation, processing objectives including factors influenceing  food acceptability and preferences, packaging and water, waste disposal and sanitation.

The kind of careers that a food scientist might follow include food development, quality control, sensory specialist, flowur chemist, food safety research and education. It si because of food science amazing achievements have taken place in the food industry. It is a fact that the food industry is able on the most part to supply the cheap, healthy and safe food.

Genet

Ecology – relation of plants and living creatures to each other and thieir environment

                         

                        CARBOHYDRATES

Energy that is needed to move, perform work and live is chiefly consumed in the form of carbohydrates. Carbohydrates, primarily starches, are least expensive, easily obtained and readily digested form of fuel.

COMPOSITION

Carbohydrates are organic compounds composed of carbon, hydrogen and oxygen, with the later elements in the ratio of 2:1. The general formula is CnH2nOn. They are viewed as hydrated carbon atoms.

CLASSIFICATION – SIMPLE AND COMPLEX :

Carbohydrates are classified, depending on the number of sugar units they contain, as simple carbohydrate and complex carbohydrates.

Monosaccharides and disaccharides make up simple carbohydrates, called simple sugars containing one and two sugar units respectively. Polysaccharides called complex carbohydrates are structurally larger and more complex than simple sugars. They include starch, dietary fibre and glycogen.

There are two main classes of monosaccharides based on the carbonyl group present in them. They are aldoses and ketoses, aldoses (eg; glucose) containing the aldehyde group (CHO) and ketoses, (eg;- fructose) containing the ketone group (C=O). Aldoses are further divided into trioses, tetroses, pentoses and hexoses based on the number of carbon atoms. The common disaccharides are Maltose, Lactose and Sucrose which on hydrolysis yield two monosaccharide units.

Maltose hydrolysis Glucose + Glucose

Lactose hydrolysis Glucose + Galactose

Sucrose hydrolysis Glucose + Fructose

Polysaccharides have high molecular weight and are insoluble in water. They are in the form of long chains either branched or un branched.

The polysaccharides are further classified into groups depending upon the products they yield on hydrolysis.

Homopolysaccharides yield only one type of monosaccharide units on hydrolysis e.g.:- starch, dextrin, cellulose, glycogen.

Heteropolysaccharides yield more than one type of monosaccharide units on hydrolysis e.g.:- Heparin, Hyaluronic acid.

Heparin is an anticoagulant found in the liver, spleen, lungs and blood. Hyaluronic acid is found in the umbilical cord, synovial fluid and vitreous humour. It has a lubricating action. In tissues it forms an important part of the cementing ground substance.

The sugars are also classified as reducing and non reducing sugar. The reducing property is attributed to the free aldehyde or keto group.

FUNCTIONS

Carbohydrates perform the following functions.

1. Energy:

The principle function of carbohydrates is to serve as a major source of energy for the body. Each gram of carbohydrate yields 4Kcal of energy regardless of its source. In Indian diets 60 – 80 % of energy is derived from carbohydrate.

2. Glucose:

Glucose is indispensable for the maintenance of the functional integrity of the nervous tissue and is the sole source of energy for the proper functioning of the brain. Prolonged lack of glucose may cause irreversible damage to the brain.

3. Protein Sparing Action:

Carbohydrates exert a protein sparing action. If sufficient amounts of carbohydrates are not available in the diet, the body will convert protein to glucose in order to supply energy. Hence to spare proteins for tissue building, carbohydrates must be supplied in optimum amounts in the diet. This is called the protein sparing action of carbohydrates.

4. Fat Metabolism:

Carbohydrates are essential to maintain normal fat metabolism. Insufficient carbohydrates in the diet results in larger amounts of fat being used for energy than the body is equipped to handle. This leads to accumulation of acidic intermediate products called ketone bodies.

5. Synthesis of Body Substances:

Carbohydrates aid in the synthesis of nonessential aminoacids, glycoproteins (which function as antibodies) and glycolipids (which form a part of cell membrane in body tissues especially brain and nervous system). Lactose remains in the intestine longer than other disaccharides and thus encourages growth of beneficial bacteria.

6. Precursors of Nucleic Acid:

Carbohydrates and products derived from them, serve as precursors of compounds like nucleic acids, connective tissue matrix and galactosides of nervous tissue.

7. Detoxification Function:

Glucuronic acid, a metabolite of glucose serves as a detoxifying agent. It combines with harmful substances containing alcohol or phenolic group converting them to harmless compounds which

are later excreted.

8. Roughage of the Diet:

Insoluble fibres known as composite carbohydrates can absorb water and give bulk to the intestinal contents which aids in the elimination of waste products by stimulating peristaltic

movements of the gastrointestinal tract.

Types of Carbohydrates

Carbohydrates can be classified on the basis of their chemical composition. These are the most easily available and the largest set of compounds on the Earth. Based on the complexity of their structures, there are five major classes of carbohydrates. These are described in brief as follows.

Monosaccharides

These are the basic compounds with a cyclic structure consisting of carbon, hydrogen and oxygen in the ratio 1:2:1. 'Mono' refers to single and saccharides means sugar. Glucose, fructose and galactose are types of monosaccharides.

Disaccharides

These carbohydrates mean 'two sugars', which refer to the commonly available types such as sucrose, maltose and lactose. When two monosaccharides bond together by a condensation reaction, they release one molecule of water and a disaccharide is formed. This bond is called a glycosidic bond.

Oligosaccharides

These are carbohydrates with more than two basic types of sugar molecules, usually between three and ten basic units. Their main function in the body is the storage of glucose. Raffinose and stachyose are the main types of oligosaccharides which consist of repetitive chains of fructose, galactose and glucose.

Polysaccharides

These are also called monomers and are composed of thousands of molecules of the basic units of glucose. Carbohydrates stored in the form of starch contain these type of compounds. Amylose, which is a straight chain compound and amylopectin, which is a branched compound, are the most common types of polysaccharides.

Nucleotides

It is another complex carbohydrate which contains many molecules of cyclic sugar. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are complex five sided sugars classified under this category. The difference between RNA and DNA is that the former has one extra hydroxyl group.

Effect of cooking on starch:

1.      Dry Heat Effect: It leads to dextrinization. It is the process by which the large starch structures enmeshed together is broken down into smaller polysaccharides till dextrins are formed. This process has following effects :

2.      A. Dextrins reduce the thickening power of the starch in the foods.

B. Bring about surface browing and colour to food like toasted roasted and baked products.

C. Changes the flavor as experienced with bread and toast.

D. Changes the texture of final products which become crispon the surface but retain their juiciness and natural flavours.

E . Imparts a delicate sweetness to products

F. Improves digestibility of starch food.

Effect of Moist Heat:

When starch or starchy food is subjected to moist heat the starch granules take up the water and swell. The granular wall burst and the starchy contents spill out to mingle with water to form a solution which is milky in appearance.

Gelation: Even starch has a temperature range with in which the starch becomes more viscous and forms a gel, which resists flow. The process by which it takes place is called gelation.

Gelatinization: gels (viscous mixture) on further heating the solution become transparent and forms a network of amylose, amylopectin and water held together by intermolecular bonds. All the free water gets enmeshed in a matrix indirected by a coating on the back of the spoon. The hot mixture when poured into a mould and allowed to cool, sets into a form structure which when unmoulded retain the shapes of the container. This process is called gelatinization.

Synerisis : When a moulded starch is kept for  a time in the refrigeration or cut and after that put into some hot water for a while so that starts and comes out of the structure which is distributed . This process is reference is synerisis.

Retrogradation : when some cooked gels showing synerisis inhibit further realignment of the amylopectin fractions to further after the structure the process is termed as the retrogradation.

Uses of Starches in Food Preparation:

1.      Thickening: Starch in the form of the corn flour, refined wheat flour, rice flour and arrow root are used for thickening. The gravies, soups, puddings etc.

2.      Binding : in cutlets

3.      Coating: Starches are often used in the form of pabtis to coat food before frying. This gives the products crispness and seals in the flabour by forming a barrier to evaporation of food contents and provides smooth and golden apprearance to the product by any crevices or irregularities on the surface.

4.      Gelling: Provides the gelling in porridge and puddings.

5.      Browning: It provides the browning to the following products such as toast or chappati due to dextrinization.

Sugars

Sugars are classified as

1.      Monosaccharides:- glucose, galactose, fructose

2.      Disaccharides- Maltose, lactose and sucrose

3.      Polysachharides – glycogen, dexrrin, pectin, starch etc.

Uses of sugars:

1.      Candies  - burfies, caramels, chewy and gummy products

2.      Syrup – sugar syrup it may be single thread, two thread or three thread

3.      Crystals – sugar crystals.

4.      Invert sugar – when sucrose is heated in the presence of acid/ enzyme equal amount of dextrose and lacillose are formed this mixture is known as invert sugar

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                             FATS AND OILS

Fats are an important component of the diet and is present naturally in many foods. Fats are solid at room temperature while oils are liquid. Fats in the diet can be of two kinds viz., the visible and the invisible fat.Invisible fats are those present inherently in foods. Example of food containing appreciable quantities of invisible fat include meat, poultry, fish, dairy products, eggs, nuts and seeds. Visible fats are those fats that are made from these products. They are cooking oils, salad oils, butter, ghee and margarine.

NUTRITIONAL SIGNIFICANCE

· They are a concentrated source of energy. One gram of fat contributes 9 kilocalories as against 4 kilocalories contributed by carbohydrates and protein.

· They are a good source of vitamin A,D,E and K.

· They provide essential fatty acids which are components of

membranes of living cells.

· They impart special flavour and texture to our foods, thus

increasing palatability.

· They are also used by the body to make prostoglandins

involved in a large variety of vital physiological functions.

REFINED OILS

Oils and fats do not occur free in nature. They occur in animal tissues and in seeds and fruits from which they are isolated. The extracted oils are crude and contain many constituents like free fatty acids, unsaponifiable matter, gums, waxes, mucilaginous matter, variety of colouring matter, metallic contaminants and undesirable odour producing constituents. In refining these constituents are removed by the following steps:

· Suspended particles are removed by filtration or centrifugation.

· Free fatty acids are removed by alkali treatment.

· Any remaining free fatty acids are removed by neutralisation.

· Pigments are removed by bleaching using adsorbents like activated earth or carbon and sometimes chemical bleaching agents.

· The oil is finally deodorized by injecting steam through the heated fat under reduced pressure to obtain refined oil.

HYDROGENATION – VANASPATHI AND MARGARINE

Plant oils contain a large percentage of unsaturated fatty acids and hence have a tendency to become rancid. These unsaturated glycerides in oil can be converted to more saturated glycerides by the addition of hydrogen. This process is known as hydrogenation.

Hydrogenated fat is manufactured from vegetable oils by the addition of molecular hydrogen to the double bonds in the unsaturated fatty acids in the presence of nickel. The double bonds take up hydrogen and saturated fatty

acids are obtained. By this process, liquid fats can be converted to semi solid and solid fats for use as shortening in the preparation of biscuits, cakes and butter substitutes.

Hydrogenation is of great economic importance because it allows oils to be converted into fats, which have better keeping quality.As hydrogenated fats are prepared from refined deodourised oils, the resulting fats are odourless and colourless and blend well in several food preparations.

Vanaspathi:

Hydrogenated oil in India is known as vanaspathi. It is manufactured by hydrogenating refined groundnut oil or a mixture of groundnut oil with other edible vegetable oils. According to vanaspathi control order, the melting point of vanaspathi should be between 31°C and 37° C and it should contain 5 percent sesame oil and should be fortified with vitamin A.

Margarine :

Margarine is often used as a substitute for butter. It is made from vegetable oils or a mixture of vegetable and animal fat by hydrogenation. It is then blended with cultured skim milk and salt. The fats most commonly used in the manufacture of margarine are cotton seed oil, soyabean oil, corn oil, groundnut oil, coconut oil and meat fat. Additional additives may include diacetyl for butter flavour, sodium benzoate for preservation, mono and diglycerides or lecithin for emulsification, yellow colouring matter and vitamin A and D.

Winterization : some cooking oil become cloudy when they are stored in the reftrigerator. This occurs because some of the triglyceride molecules in the oil have higher melting points than other molecules in the mixture and crystallize or become solid at the lower temperature. In manufacturing oils intended to be used primarily for the making of salad dressings, a winterizing process is applied. In this process, the temperature of the oil is lowered to a point at which the higher melting triglycerides crystallize. Then the oil is filtered to remove the crystal the remaining oil has a lower melting point and does not crystallize at refrigerator temperature. It is referred to as salad oil. Removing the solid particles is called winterization

Leavening :  When fats are creamed with sugars as in preparation of cake, butters, they help to incorporate air into the batter making it tight and foamy. On baking the protein films coagulate enclosing the air and making the end products light in texture and soft in mouthfeel. In biscuits since foaming is not required the fat is rubbed into the flour gently to provide slight aeration to impart a light crisp texture.

Shortening : Fats provide a crumbly texture to food by foaming a film around the starch and protein particles in flours preventing the formation of long gluten strands in them. This accomplished when fat is rubbed into a flour gently using the tips of the fingers only. Such treatment to flours before dough formation makes products soft and tender or short after cooking. This effect is called shortening and is used for making biscuits, cakes pie bases, pastry products etc. where a golden color and crisp texture is required through baking and frying.

RANCIDITY

Fats and oils undergo certain undesirable changes during storage which result in spoilage. The major spoilage of fats and oils is rancidity. Rancidity refers to the development of disagreeable odour and flavour in fats and oils owing to specified chemical reaction such as oxidation and hydrolysis. Hydrolysis is the decomposition of fats into free fatty acid and glycerol by enzymes in the presence of moisture. These free fatty acids released are responsible for the unpleasant flavour and odour. During oxidation, oxygen is added to the unsaturated linkage and this results in the formation of peroxides. These

peroxides decompose to yield aldehyde and ketones which are responsible for the pronounced off flavour. Rancidity may also be caused by the absorption of odour and action of micro organism and enzymes.

Prevention of rancidity :

· Storage in coloured glass containers prevent oxidation of fats by rays of light.

· Vacuum packaging retards rancidity by excluding oxygen.

· Naturally occurring antioxidants like vitamin C, b carotene and vitamin E protect against rancidity.

· Synthetic antioxidants like butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT) and propylgallate can also be added to prevent rancidity.

Types of Rancidity

There are 3 main types of Rancidity :

a)    Hydrolytic Rancidity: Hydrolysis of fats by lipase need not always produce off flavours. Butter fat and coconut oil, butyric acid are set free by hydrolysis of lipase . the odours of these acids contribute largely to the smell of rancid butter.

b)    Oxidative Rancidity : Common type of rancidity observed in all fats and oils. Addition of oxygen to the unsaturated linkage results in the formation of peroxide which on decomposition yields aldehydes and ketones having off flavor.

c)    Ketonic Rancidity : As a result of action of fungi such as Aspergillus Niger, penicillium glaucum on coconut and other oil seeds.

SMOKING POINT

When fats and oils are heated to a high temperature, decomposition of fat occur and finally a point is reached at which visible fumes are given off. This is called smoking point and the temperature is called smoking temperatures of fat.

Smoking temperature is defined as the lowest temperature at which visible fumes consisting of volatile gaseous products of decomposition are evolved. Beyond the smoke point is the flash point where the combustion occurs.

Factors affecting smoking temperature of fats and oils :

1. The amount of free fatty acids present.

2. The surface of oil exposed while heating.

3. The presence of mono and diglycerides and foreign particles such as flour particles. Smoking temperature is important for fats used for frying. Fats with low smoke point are not suitable for frying because of the odour and irritating effect of the fumes. The decomposition products may also give an unpleasant flavour to the food. Hence it is preferable to use fats with relatively high smoking temperatures for frying.

The smoking points of some fats and oils are given

below :

Smoking points of some fats and oils

Oil or fat Smoking temperature (° C)

Soyabean oil 230

Hydrogenated fat 221

Butter fat 208

Groundnut oil 162

Coconut oil 138

Flavour Reversion: Many refined oils undergo change in flavor before the onset of rancidity. This process is known as reversion. This is due to the fact that such fatty acids undergo oxidation rapidly when exposed to air and decomposition products termed contribute to the off flavor.

ROLE OF FAT / OIL IN COOKERY

· Fat is used as a medium of cooking in shallow and deep fat frying.

· Fat improves the texture of food. e.g., cake, biscuit, cookies.

· Fats help in leavening – in making cake, leavening occurs by incorporating air into the fat during the leavening process.

· Fat increases smoothness of the product e.g., Halwas, crystalline candies.

· Fats are shortening agents- one of the most important function of fat is to shorten baked products which otherwise are solid masses firmly held together by strands of gluten.

· Fat improves palatability – fat gives taste and flavour to the food.

Properties of Fats :

1.     Solubility : Fats are soluble in ethyl ether, petroleum ether, acetone, hot alcohol and benzene. The quantity of fat present in food materials is determined by extraction with ethyl ether or petroleum ether.

2.     Saponification Value : THE saponification value is defined as the number of mg of potassium hydroxide required to saponify 1g of fat or oil.

3.      Iodine Value : Measure of the extent of unsaturated fatty acids present in fats and oils. It is defined as the number of grams of iodine absorbed by 100g of fat.

4.     Acid Value : No of mg of potassium hydroxide required to neutralize the free fatty acids in 100 g of oil or fat. This value is expressed as percentage of oleic acid.

5.     Reichert – Meissle Value :  No. of ml of 0.1 Nitrogen Alkali required to neutralize steam volatile water soluble fatty acid present in 5g sample.

6.     Thicocyanogen Value : Amount of Thicocyanogen absorbed by 100g of fat or oil.

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