Food Constituents: Dr. Kashif Khan

FOOD CONSTITUENTS Dr. Kashif Khan

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Water

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Water  Human body contains 60-70% water  Source:  Food  Drinks  Produced in the body by oxidation of carbohydrates, proteins and fats  Water content is present in all foods except few like Common salt, sugar and vegetable cooking oil 3

Nature of water in food  It is present in 3 forms

 Free water, available for chemical and biochemical reactions  in tomatoes  orange juice  Chemically bond, linked to carbohydrates and salts, difficult to remove  Sugar  Physically bound  emulsions and gel  The bound water reduces chemical and biochemical reactions as well as 4 microbial activity

ERH (Equivalent relative humidity)  Stability increases with lowering of water content in foods  0-25% ERH o Water is unfree able o Food is quite stable  25-80% ERH o Auto-oxidation occurs in such foods o Freezing point is reduced or unfree able o Food is liable to deteriorative changes like non-enzymatic browning, enzyme activity, hydrolytic and oxidative reactions 5

Conti…  80-90% ERH o Reduction in freezing point of tissues

o Growth of microorganisms o Enzyme activity, oxidative and hydrolytic reactions occur o Non-enzymatic browning takes place

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Food Solutions  These are dispersions in which solid and semisolid particles are evenly distributed in water.

 These are of 2 types 1. Colloidal solutions 2. Coarse solutions

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Colloidal Solutions  These are made up of long chain macromolecules  Aggregated molecules of proteins, polysaccharides and lipids  solutions containing gums, pectic substances, proteins and lipids  Jams, jellies and milk

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Coarse Solutions

 Macroparticles are crystals, semi-crystalline aggregates, amorphous flocks  ketchup

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Food Gel  Type of dispersion

 consists of continuous phase of interconnected particles  intermingled with a continuous water phase  These gels have  various degree of rigidity  elasticity  and  brittleness  depending upon gelling agents  pectin, carboxymethyl cellulose, cornstarch, hums 10

Conti…  Properties of gel depends upon o Concentration of gelling agent o pH o Temperature  Examples o Jams o Jellies o Marmalades 11

Emulsion  Definition:  It is a dispersion in which two immiscible liquids are dispersed.

 It is usually unstable as the dispersed droplet floats over  Emulsifying agents increases the stability of the emulsion  It has two phases 1. Dispersion phase (droplets of one liquid) 2. Continuous phase (the other liquid) 12

Conti…  o o  o  o

Food emulsions consists of Water A plastic liquid (like oil, fat, wax etc.) Water in oil emulsion: Example: butter and margarine Oil in water emulsion: Example; milk, cream and mayonnaise

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Functions  Essential for all biochemical reactions  Medium in which nutrients, enzymes and other chemical substances are dispersed  Act as a reactant in hydrolysis reactions  Transport nutrients and removes waste

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Carbohydrates

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Carbohydrates  Chemically contain: Carbon-Hydrogen-Oxygen  Carbohydrates are converted into monosaccharides in digestive tract

 Source:  Cereals (rice, corn and their products)  Roots and tubers (potatoes and sweet potatoes)  Fruits and vegetables (sugar and fiber)

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Simple Carbohydrates ■ Cannot be hydrolyzed further into simpler ■ Contains monosaccharides and disaccharides

■ E.g. glucose, fructose and galactose ■ Monosaccharide condense to form compound carbohydrates

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Complex Carbohydrates ■ Can be hydrolyzed into monosaccharides ■ Contains oligosaccharides and polysaccharides

■ E.g. amylose, amylopectin ■ 3-7 monosaccharides condense to form oligosaccharides

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Functions ■ Source of energy ■ Yields 16kJ (3.75 kcal) of energy/g after oxidation

■ Excess carbohydrates are stored as glycogen and rest into fat for storage in adipose tissues

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Lipids

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Lipids  Chemically contains: Carbon, hydrogen and oxygen  Soluble in organic solvent and insoluble in water  Source: Fats and oils  Emulsion: Fats and oils can be made to mix with water in the presence of emulsifier. The product formed when two immiscible solvent states are made miscible in the presence of emulsifier is known as emulsion

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Conti… Rancidity: How food is spoiled?  Storing fats and oils for long time changes its odour as a result of oxidative reaction  The reaction yields peroxides and hydroperoxides which later breaks up into odorus compounds like aldehydes, ketones, alcohol etc.  This reaction can be triggered by high temperature, light and water 22

Fats ■ Solid at room temperature ■ Contains saturated fatty acids (no double bond)

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Oils ■ Liquid at room temperature ■ Contains Unsaturated fatty acids (double bond present)

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Functions ■ Source of energy ■ Yields 38 kJ (9 kcal) of energy/g on oxidation

■ Excess is stored in adipose tissues which act as energy reserve ■ Maintains constant body temperature by providing an insulating layer between body and skin

■ Protect vital organs against injury ■ Fats and oils are good source of vitamin A, D, E and K 25

Proteins

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Proteins  Amino acids are building blocks  Children need more protein for growth and building body tissues  Sources:  Animal (lean meat, poultry, fish, sea food, eggs, milk, cheese)  Beans, nuts, pulses (ground nuts, almonds etc)  Plants (cereals provide poor quality protein ) 27

Conti…  Deficiency of protein may cause Kwashiorkor

 A condition characterized by depigmentation and edema

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Types of amino acids Essential amino acids  Human body cannot synthesize or synthesize is insufficient

Non- essential amino acids  Synthesized from other amino acids in the human body

 Sources: Must be included in food

 E.g. alanine, arginine, cysteine

 Animal (milk, eggs, meat and fish)

 Plants (cereals, legumes and leafy vegetables)  E.g. histidine, isoleucine,

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Functions  In human body  Building and maintenance of tissues  Repair of muscles and tissues  Source of energy  Yields 17 kJ (4 kcal) of energy/g

 Act as enzymes, biological catalyst  Act as hormones, regulating different functions  Act as antibodies, fight against infections 30

Conti…  In foods protein is used for:  Solubility, foaming , emulsification, gelling ability and nutritional quality

 In meat products, baked goods  Hospital and vegetarian food preparation  Infant formula preparation

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