Food is any substance normally eaten or drunk by living things. The term food also includes liquid drinks. It is the main source of energy and nutrition for animals, and is usually of animal or plant origin. There are four basic food energy sources – fats, proteins, carbohydrates and alcohol. Proteins, fats and carbohydrates in food provide the energy or kilocalories for the functioning of body. Each gram of protein and carbohydrates has 4 kilocalories; each gram of fat has 9 kilocalories.
The most important food constituents are classified as:
I. Major Food Components – Water, protein, carbohydrates and fats
II. Minor Food Components – Food phenolics, natural emulsifiers, organic acids, oxidants and antioxidants, enzymes, pigments and colors, flavors, vitamins, minerals, analogs and new ingredients
Water is abundant in all living things and consequently is in almost all foods. It is essential for life, even though it contributes no calories to the diet. Water greatly affects the texture of foods. It gives crisp texture or turgor to fruits and vegetables and also affects perception of the tenderness of meat. For some food products, such as potato chips, salt, or sugar, lack of water is an important aspect of their quality and keeping water out of such foods is important to maintain quality.
Almost all food processing techniques involve the use of water or modification of water in some form – freezing, drying, emulsification (trapping water in droplets), and bread making, thickening of starch, and making pectin gels are few examples. Since bacteria cannot grow without water, the water content has been a significant effect on maintaining quality of the food.
So freezing, dehydration, or concentration of foods increases shelf-life and inhibits bacterial growth. Water is important as a solvent or dispersing medium, dissolving small molecules to form true solutions and dispersing larger molecules to form colloidal solutions.
Acids and bases ionize in water; water also is necessary for many enzyme- catalyzed and chemical reactions to occur, including hydrolysis of compounds such as sugars. It is also important as a heating and cooling medium and as a cleansing agent. Because water has so many functions that are important to a food scientist, it is important to be familiar with some of its unique properties.
Proteins are the most abundant molecules in cells, making up 50% or more of their dry weight. Every protein has a unique structure and conformation or shape, which helps to carry out a specific function in a living cell. Proteins comprise the complex muscle system and the connective tissue network, and they are important as carriers in the blood system.
All enzymes are proteins; enzymes are important as catalysts for many reactions in foods. All proteins contain carbon, hydrogen, nitrogen, and oxygen. Most proteins contain sulfur and some contain additional elements; for example, milk proteins contain phosphorus and hemoglobin and myoglobin contain iron. Copper and zinc also are constituents of some proteins. Proteins are made up of amino acids.
There are at least 20 different amino acids found in nature, and they have different properties depending on their structure and composition. Small changes, such as a change in pH or simply heating a food, can cause dramatic changes in protein molecules. Such changes are seen when cottage cheese is made by adding acid to milk or when scrambled eggs are made by heating and stirring eggs.
Proteins are very important in foods, both nutritionally and as functional ingredients. Proteins may provide around 4 kilocalories of energy per gram. They play an important role in determining the texture of a food. They are complex molecules, and it is important to have an understanding of the basics of protein structure to understand the behavior of many foods during processing.
Protein in food contributes essential amino acids to our diet. Amino acids are used by cells to build new proteins and repair the muscles, bone, skin, organs and blood. Without protein, cuts and abrasions will not heal quickly, muscles will not grow and the blood does not clot correctly. Our body uses proteins for growth and to build hormones, antibodies and the enzymes that regulate the chemical reactions within the body. Protein food is not a high source of energy; however protein is essential in the right amount for proper functioning of our body.
Proteins perform different functions in food products depending on their physical shape and chemical structure. The structure of protein changes due to heat, salts, pH and mechanical action. This process is called denaturation. When proteins unfold from their coiled state and form a solid network, they coagulate, or set, e.g., a boiled egg.
The amount and type of protein present in flour determines its suitability for use in different products, e.g., bread required strong flour with high protein content. Meringue, cheese, bread and jelly are examples of food products which use the functional properties of protein. Common protein rich foods include milk, soya milk, eggs, cheese, yogurt, peanut butter, lean meats, fish, and poultry, beans, tofu, lentils, and other legumes, grains, including bread and pasta, nuts and seeds.
Protein requirements depend on a child’s age and weight. For example – an average 4-6 year old preschooler requires about 22 grams of protein per day, while an older 7-10 year old requires about 28 grams of protein per day.
In addition to foods that naturally have a lot of proteins in them; we can also buy protein supplements, such as protein fortified drink mixes, including PediaSure or Carnation instant breakfast. Certain food that can combine more than one protein rich food, such as a cheeseburger, which includes meat, cheese, and a bun.
The other types of protein fortified foods include Tuna fish sandwich, cheeseburger, cheese pizza, peanut butter and jelly sandwich, macaroni and cheese grilled cheese sandwich, etc. Vegetables, legumes and fruits are good sources of protein.
Generally, legumes have higher content of protein than vegetables and fruits. The advantage of plant protein sources over animal protein is that plant protein sources are low in fat content and high in dietary fiber. Protein in plants (except soya bean) is incomplete, meaning all the essential and non-essential amino acids are not present in a single plant. The most important function in protein food to provide essential amino acids and non-essential amino acids
Amino acids are the smallest unit of protein and can be defined as an organic molecule made up of amine and carboxylic acid functional groups – an amino acid is composed of nitrogen, carbon, oxygen and hydrogen molecules. Essential amino acids, also called limiting amino acids, are those that cannot be produced in our body and therefore have to be obtained from food sources.
There are 8 essential amino acids:
7. Methionine, and
Amino acids are useful components in a variety of metabolisms. They are the part of complex pathways and biological systems. The function and use of an amino acid is dependent on other amino acids, mineral elements, carbohydrate and fatty acids and has indirect effects that are manifested in myriad metabolisms.
The functions of essential amino acids are listed below:
It is necessary for the synthesis of neurotransmitter serotonin.
It is precursor of dopamine, nor epinephrine and adrenaline. It enhances positive mood. It is also an antioxidant.
It is essential for muscle development.
It is necessary for the synthesis of hemoglobin, major constituent of red blood cells.
It is beneficial for skin, bone and tissue wound healing. It promotes growth hormone synthesis.
It is a component of muscle protein, and is needed in the synthesis of enzymes and hormones.
It is an antioxidant. It helps in breakdown of fats and aids in reducing muscle degeneration. It is also good for healthy skin and nail.
It is beneficial for healthy nervous system. It boosts memory and learning.
Non-essential amino acids are amino acids that can be produced in our body. Their uses and functions in our body are equally as important as the limiting amino acids but the difference is that those kinds of amino acids can be found in our diet. The remaining 12 amino acids come under non-essential amino acids, e.g., alanine, cysteine, glutamine, glycine, histidine, threonine, aspargine, proline, etc.
Carbohydrates are organic compounds containing carbon, hydrogen, and oxygen, and they may be simple or complex molecules. The important food carbohydrates include simple sugars, dextrins, starches, celluloses, hemicelluloses, pectins, and gums. They are important source of energy or fiber in the diet, and they are also important constituents of foods because of their functional properties.
The carbohydrates in our diet come from plant foods. Carbohydrates are so-called because they are essentially hydrates of carbon. Specifically they are composed of carbon and water and have composition of Cn(H2n O). The simplest carbohydrates are known as monosaccharides or sugars, and they have the general formula CnH2nOt.
The most common ones contain six carbon atoms. Disaccharides contain two sugar units, trisaccharides contain three, oligosaccharides contain several units, and polysaccharides are complex polymers containing as many as several thousand units linked together to form a molecule.
All are complex carbohydrate polymers with different properties, which depend on the sugar units that make up the molecule, the type of glycosidic linkages, and the degree of branching of the molecules. Starch is a plant polysaccharide stored in roots and seeds of plants. It provides humans with energy (4 kcal per gram) and is hydrolyzed to glucose, supplying the glucose that is necessary for brain and central nervous system functioning.
Starch grains, or granules, contain long-chain glucose polymers and are insoluble in water. Unlike the small molecules of salt and sugar, the larger starch polymers do not form a true solution but starch granules form a temporary suspension when stirred in water. Once starch is cooked, the swelling is irreversible and the starch leaches out. This characteristic of starch granules enable starch to be used as a thickener.
The characteristics of a finished starch food product are determined by several factors: The source of starch, concentration of starch used in a formulation, the temperature of heating, and other components used with the starch, such as acid and sugar.
Carbohydrates perform several functions in food:
(a) It may be used as sweeteners, thickeners, stabilizers, gelling agents, and fat replacers.
(b) Contributing to texture (starch, gluten).
(c) Hygroscopic nature/water absorption.
(d) Providing source of yeast food.
(e) Regulating gelation of pectin dispersing molecules of protein or starch.
(f) Preventing spoilage.
(g) Delaying coagulation of protein.
(h) Giving structure due to crystals.
(i) Affecting osmosis.
(j) Affecting color of fruits.
(k) Affecting texture (viscosity, structure).
(l) Contributing flavor other than sweetness.
The most important types of sources of starches are cereal grains such as wheat, corn, or rice. Wheat yields a cloudy, thick mixture, while cornstarch produces more clear mixtures such as gravies or sauces. Vegetables, roots and tubers, including the root of cassava, and potatoes frequently are used in the preparation of gluten-free foods. Another source of starch is a legume such as soya beans. Sago is a powdery starch obtained from the stems and trunks of the sago palm in tropical Asia. Fruits also may be sources of starch. An example is the banana.
Gums are a group of complex hydrophilic carbohydrates containing thousands of monosaccharide units. Galactose is the most common monosaccharide found in gums; glucose is usually absent. Gums are often referred to as hydrocolloids, because of their affinity for water and their size; when added to water, they form stable aqueous colloidal dispersions or sols.
The molecules are highly branched and as a result most gums are unable to form gels. So they are able to trap or bind large amounts of water within their branches. Gums are classified as soluble fiber because, they undergo little digestion and absorption in the body. Therefore, they supply relatively few calories to the diet, as compared with digestible carbohydrates such as starch.
Main Characteristics of Gums:
The most important characteristics of gum are: It is a large highly branched hydrophilic polymer and rich in galactose. It is often known as hydrocolloids and it form viscous solutions. Most of the gums do not form gel.
Gums are common in a wide range of food products, including salad dressings, sauces, soups, yogurt, canned evaporated milk, ice cream and other dairy products, baked goods, meat products and fried foods. They are used as thickening agents in food products, replacing starch.
They also are used to assist in the stabilization of emulsions and to maintain the smooth texture of ice cream and other frozen desserts. They are common in reduced fat products, because they are able to increase viscosity and help to replace the texture and mouth feel that was contributed by the fat.
Gums are obtained from plants and can be separated into five categories – seed gums and plant exudates, microbial exudates, seaweed extracts, and synthetic gums derived from cellulose.
1. Seed gums – guar gum and locust bean gum
2. Plant exudates – gum arabic and gum tragacanth
3. Microbial exudates – xanthan, gellan and dextran
4. Seaweed polysaccharides – alginates, carrageenan and agar
5. Synthetic gums – microcrystalline cellulose, carboxymethyl cellulose and methyl cellulose
Gums may be used to perform so many roles in food products.
They are listed below:
1. Thickeners – salad dressings, sauces, soups and beverages
2. Stabilizers – ice creams, icings and emulsified products
3. Control crystal size – candies
4. Suspending agents – salad dressings
5. Gelling agents – fruit pieces and cheese analogs
6. Coating agents- batters for deep-fried foods
7. Fat replacers- low-fat salad dressings, ice creams and desserts
8. Starch replacers- baked foods, soups and sauces
9. Bulking agents- low fat foods, and
10. Source of fiber- beverages, soups and baked goods.
Mucilage is another soluble fiber present in some food items. It is an exopolysaccharide; a polymer present in certain plant foods. It is a naturally occurring, high-molecular-weight (200,000 and up), organic plant product of unknown detailed structure. Mucilages are dietary fibers that contain galactose, mannose, and other monosaccharides; gums are dietary fibers that contain galactose, glucuronic acid, and other monosaccharides.
Chemically, mucilage is closely related to gums and pectins but differs in certain physical properties. It occurs in various parts of nearly all classes of plant, usually in relatively small percentages, and is frequently associated with other substances, such as tannins and alkaloids.
Although gums swell in water to form sticky, colloidal dispersions and pectins gelatinize in water, mucilages form slippery, aqueous colloidal dispersions. Mucilage in plants helps in water storage and seed germination, and acts as a membrane thickener and food reserve. Mucilages are formed in normal plant growth within the plant by mucilage-secreting hairs, sacs, and canals, but they are not found on the surface as exudates.
These types of exopolysaccharides are the most stabilizing factor for micro aggregates and are widely distributed in soils. Therefore exopolysaccharide-producing “soil algae” play a vital role in the ecology of the world’s soils. The chief industrial sources of mucilages are ice landic and Irish moss, linseed, locust bean, slippery elm bark, and quince seed.
Mucilage is edible, but tastes rather bland. It is used in medicine for its demulcent properties. Traditionally marshmallows were made from the extract of the mucilaginous root of the marshmallow plant and due to the demulcent nature of the extract, worked as a cough suppressant. It is used as a type of glue for paper.
Some carnivorous plants with mucilage are used for the traditional production of a dairy product in Sweden, called filmjolk. During the fermentation of natto soyabean, certain enzymes react with soyabean sugars to produce mucilage. The amount and viscosity of the mucilage are important natto characteristics and contribute to natto’s unique taste and smell.
Fat is a principal component of the diet. It is important due to its flavor/mouth feel, palatability, texture and aroma. Fats also carry the fat-soluble vitamins A, D, E, and K. Sources of fats and oils may be animal, vegetable, or marine which may be manufactured in some combination in industrial processing.
Fats appear solid at room temperature, whereas oils are liquid at room temperature. One gram fat may provide 9 k calories of energies. Some fats are essential, such as linolenic and linoleic fatty acids, indicating that either the body cannot make them or cannot make enough fats or oils are insoluble in water and have a greasy feel that the consumer may feel. Fats may be processed into monoglycerides and diglycerides and they may be added to many food products functioning as emulsifiers.
Some of the functions of fat in food preparation are as follows:
(i) Add or modify flavor, texture
(ii) Aerate (leaven) batters and dough in bread making.
(iii) Contribute flakiness
(iv) Contribute tenderness
(vi) Transfer heat, such as in frying
(vii) Prevent sticking, and
(viii) Provide satiety.
Phenolic food compounds (also known as aromatic food compounds) occur naturally in all foods. They give the food color and flavor and help to prevent premature decomposition.
An emulsifier (also known as an emulgent) is a substance which stabilizes an emulsion, a surfactant. An emulsion is a mixture of two or more immiscible (unbendable) liquids. One liquid (the dispersed phase) is dispersed in the other (the continuous phase), i.e. material that keep fat globules in water droplet or water droplet in fat are emulsifiers.
Lecithins and other phospholipids emulsifiers are the best emulsifiers which are present in animal and plant tissues and in egg, milk, and blood. Without emulsifiers we could not have stable mayonnaise, margarine, or salad dressings. They have an electrically charged or polar end (+ and – at the bottom) and a non-charged or non-polar end at the top.
The polar end of this is water loving or hydrophilic and easily dissolve in water. The uncharged or nonpolar end is fat loving or hydrophobic and easily dissolved in fats. So emulsifier dissolves part of itself in water and the other part in oil.
Fruits contain natural acids, such as citric acid of lemons and oranges, malic acid of apples, and tartaric acids of grapes. These acids give the fruit tartness and slow down bacterial spoilage. Organic acids have a wide range of textural effects in food systems due to their reaction with proteins, starches, pectins, gums, and other constituents.
The rubbery conditions of cheese, stretch ability of bread dough, viscosity of sugar syrups, spread ability of jellies and jams, and mouth feel of certain beverages, etc. are because of the acid concentration in such foods. Organic acids also influence the color of foods and inhibit the growth of disease causing bacteria in food.
Many food components are adversely affected by oxygen in the air. Fats, oils and oily flavor compounds may become rancid on excessive exposure to air. Certain vitamins are diminished in the activity by oxygen. Oxygen is oxidant; it causes oxidation of many compounds in foods.
Many natural foods contain trace amounts of copper and iron which are strong promoters or catalysts of oxidation. Antioxidants are the substances prevent oxidation. So many antioxidants are also present in food includes lecithins (also an emulsifier), vitamin C and E, sulphur containing amino acids, etc.
Foods may acquire their color from any of several sources. One major source is natural plant and animal pigments, e.g. chlorophyll gives green color to lettuice and peas, carotene gives the orange color to carrots and corn, lycopene contributes red to tomatoes and watermelons, anthocyanins contribute purple color to grapes and blue berries and oxymyoglobin gives red color to meats.
Second sources of color come from the action of heat on sugars. This is referred to as caramelization, e.g., darkening of maple sugar on heating, the color on toasting bread and brown color of caramel candy. Third source is the dark color generated due to the interaction between sugars and proteins. This is known as browning reaction or Maillard reaction. In this case an amino group of a protein reacts with aldehyde or ketone group of a reducing sugar to produce a brown color.
Many foods such as coffee contain certain organic compounds which contribute the flavor and aroma of food. These organic chemicals are highly sensitive to air, heat, and interaction with one another. The flavor and aroma of coffee, milk, meats and most foods is generally becoming less desirable as the food is handled, processed and stored.
Foods contain a great number of active enzymes. Enzymes are large protein molecules which need to present in only minute amounts to be effective. Enzymes are biological catalysts that promote a wide variety of biochemical reaction in foods.
Some important aspects of enzymes in food are following:
(i) In living fruits and vegetables enzymes control the reactions related with ripening.
(ii) Enzymes enter into a vast number of biochemical reaction in foods, they may be responsible for changes in flavor, color, texture and nutritional properties.
(iii) The heating process of food inactivates food enzymes and help to extend the storage stability of foods.
(iv) Enzymes can be extracted from biological materials and purified to a high degree. Such commercial enzyme preparations may be added to foods to break down starch, tenderize meat, clarify wines, coagulate milk protein, and produce many desirable changes.
Vitamins and minerals are essential parts of food because they are required for normal health. Vitamins are organic chemicals that must be supplied (except vitamin D) to an animal in small amounts to maintain health. Vitamins facilitate the metabolism of proteins, carbohydrates, and fats.
The vitamins are divided into two major groups— fat soluble vitamins (vitamin A, D, E and K) and water soluble vitamins (vitamin B complex and C). Minerals are needed only in small amounts, have many different function. Some mineral assists in the body’s chemical reaction and other helps to form body structure.
1. Minerals are part of all the body tissues and fluids. They are important factors in keeping physiological processes going.
2. They act in nerve responses, muscle contractions, and the changes of nutrients in foods.
3. They regulate electrolyte balance and the making of hormones.
4. They strengthen skeletal structures.
5. All mineral deficiencies are treated by adding the specific element to the diet in the form of right foods.
6. Food minerals help your body by-
(i) Keeping body fluids in proper composition
(ii) Keeping blood and bones in top form
(iii) Maintaining healthy nerve function
(iv) Regulating muscle tone and the cardiovascular system
Like vitamins, minerals enable your body to perform vital tasks such as energy production, growth, and healing. Minerals help your body grow, develop, and stay healthy. The body uses minerals to perform many different functions — from building strong bones to transmitting nerve impulses. Some minerals are even used to make hormones or maintain a normal heartbeat.
Depending on the amount in the body, minerals in the diet are classified as (trace minerals):
1. Macro minerals (major minerals)
2. Micro minerals (minor/trace minerals)
Macro minerals are the elements in which your body needs larger amounts for proper functioning of the body. Macro means “large” in Greek. The important types of macro minerals group calcium, phosphorus, magnesium, sodium, potassium, chloride, and sulfur.
Calcium is the top macro mineral when it comes to your bones. It helps build strong, healthy teeth, for chomping on tasty food.
Calcium Rich Food:
Calcium rich food includes dairy products, such as milk, cheese, and yogurt, canned salmon and sardines with bones, leafy green vegetables, such as broccoli and calcium-fortified foods — from orange juice to cereals and crackers.
Phosphorous is an essential part of all living cell. It involved in the enzyme controlled energy yielding metabolism. Phosphorous also helps control the acid-alkaline reaction of the blood. It is one of the most important content of the nucleic acid. It also helps to the formation of cells, bones and teeth.
Phosphorous Rich Food:
All animal foods (meats, fish, poultry, eggs, milk) are rich in phosphorous.
It is another macro mineral in which it supports bone mineralization, protein building, muscular contraction, nerve impulse transmission, immunity.
Magnesium Rich Food:
The most predominant magnesium rich food are spinach, broccoli, green beans, tomato juice, navy beans, pinto beans, black-eyed peas, sunflower seeds, tofu, cashews, etc.
Sodium is one of the chief extracellular ions of the body. It involved primarily with maintaining osmotic equilibrium and body fluid volume. It also maintains fluid and electrolyte balance, supports muscle contraction and nerve impulse transmissions.
Sodium Rich Foods:
These types of food include salt, soya sauce, bread, milk, meats.
Potassium keeps your muscles and nervous system working properly. Potassium helps to maintain the water content right. It maintains fluid and electrolyte balance, cell integrity, muscle contractions and nerve impulse transmission.
Potassium Rich Foods:
Bananas, broccoli, tomatoes, potatoes with skins, Leafy green vegetables, citrus fruits, like orange, dried fruits, legumes such as beans, peas, lentils, and peanuts are the popular potassium rich food.
It is another very important mineral in which it helps to maintain the osmotic balance. Chloride is also required for the production of hydrochloric acid, which is the major component in gastric juice. It maintains fluid and electrolyte balance, aids in digestion.
Chlorine Rich Foods:
Chlorine rich food includes salt, soya sauce, milk, eggs, meat.
The body needs iron to transport oxygen from lungs to the rest of your body. The entire body needs oxygen to stay healthy and alive. Iron helps because it is important in the formation of hemoglobin which is the part of red blood cells that carries oxygen throughout the body.
The important sources of iron are meat, eggs, beans, and baked potato with skins, dried fruits, like raisins, leafy green vegetables, and cereal grains, like wheat or oats. Manganese facilitates many cell processes and it is widespread in foods. Copper is necessary for the absorption and utilization of iron, supports formation of hemoglobin and several enzymes. It is present in meat and water.
Iodine is a component of thyroid hormones that help regulate growth, development and metabolic rate. It is mainly present in salt, seafood, bread, milk, cheese. Zinc is an essential constituent of enzymes involved in the carbohydrates and protein metabolism and nucleotide synthesis. Its deficiency results in impaired growth and development, skin lesion, and loss of appetite.
It is also involved in production of genetic material and proteins, transports vitamin A, taste perception, wound healing, sperm production and the normal development of the fetus. Zinc rich foods includes spinach, broccoli, green peas, green beans, tomato juice, lentils, oysters, shrimp, crab, turkey (dark meat), plain yogurt, Swiss cheese, tofu, etc. Cobalt is the primary component of Vitamin B12.
Fluoride involved in the formation of bones and teeth, helps to make teeth resistant to decay. Fluoride rich food includes fluoridated drinking water, tea and sea foods. Selenium is an Antioxidant. It works with vitamin E to protect body from oxidation. Selenium rich foods include seafood, meats and grains.
Molybdenum facilitates many cell processes and which are found in legumes and meats. Chromium is associated with insulin and is required for the release of energy from glucose. Vegetable oils, liver, brewer’s yeast, whole-grains, cheese, nuts, etc., are the best sources of chromium.
The analogues of fat, sugar and other food component mimicking the functional properties such as flavor, mouth feel, texture and appearance of the components in food. These analogs are used to replace high calorie sweeteners such as sugar or to replace fat. The use of fat replacers in ice cream is a good example of the use of such analogs.
Aspartame, which is made up of amino acids, is an example of a sugar substitute. Aspartame has about the caloric content as sucrose but is sweeter than sucrose. Even though the analogs mimic some important functions but do not behave in exactly the same way as the food component they are substituting. Similarly, Fat replacers may have the mouth feel of fat but do not carry the fat soluble flavors or vitamins of natural fat.