CHEMISTRY OF FOODS

Ch. Retnaningsih

Introduction

• Nutrition is the process by which the foods people eat provide the nutriens they need to grow and stay healthy

• Nutriens are naturally occurring chemical substances food

• There are six categories of nutrients : proteins, lipids, carbohydrates, vitamins, minerals, and water

Carbohydrates : Function in food• Flavor enchancing and sweetening due to

caramelization• Water binding• Contributing to texture (starch, gluten)• Hygroscopic nature/water absorption• Providing source of yeast food• Regulating gelation of pectin dispersing

molecules of protein or starch• Etc

Monosaccharide

• Monosaccharides may have 6 carbons and are called hexoses, or they may have 5 carbons and are called pentoses

• Glucose, fructose and galactose are three common hexoses

• Ribose and deoxyribose are two common pentoses

Disaccharides

• Two monosaccharides may be linked together to form a disaccharide

• Sucrose is the most common disaccharide and is made of one molecile each of glucose and fructose

• Lactose is major sugar in milk and is made up of one molecule of glucose and one of galactose

• Maltose is a disaccharide made from two molecules of glucose

Sugar in food

• Color, texture, and flavor are all sensory characteristics that sugar plays in most foods

• Sugars generally play a major role as a sweetener or in texture development

• As a contributor to color, sugar participates in two phenomena: the maillard reaction and carameliization

Polysaccharides

• Starch is polisaccharide made up of glucose unit linked together to form long chains.

• Starch is the storage form of energy for plants• Glycogen is the storage form of energy for

animals.• Two types of starch molecules exist-amylose

and amylopectin.

Amylose

• Amylose molecules contribute to gel formation.

• Starch begins to gelatinize between 140 F – 158 F, the exact temperature dependent is the spesific starch

Amylopectin

• The branched amylopectin molecules give viscosity to the cooked paste

Cellulose

• Cellulose is a major component of plant cell walls

• Cellulose is a polymer (long chain) glucose molecules linked together by 1 to 4 linkages and can not by digested by humans dietary fiber

Proteins

• Protein contain amino acids• Proteins are needed to build and repair body

tissue and for the metabolic functions of our body

• Amino acsids contain an amino group (-NH2) and an acid group (-COOH)

Functions of proteins include:

1. Enzymes such as tripsin and pepsin2. Storage such as ovalbumin and ferritin3. Transport such as hemoglobin and

lipoproteins4. Contactile such as actin and myosin5. Protective such as antibodies 6. Hormones such as insulin 7. Structural such as keratin, collagen

Functions of nutrions in foods

• ColorOne of the biggest roles is through the maillard reaction, a browning reaction between an amino group and a carbohydrate

• TextureCustards are protein gels where the gel strength is influenced by the ovalbumin denaturation

• FlavorAsam aminos may contribute bitterness, sweetness and other flavors

LIPIDS

• Lipids include fats and oils from plants and animals

• In foods, fats provide a source of essential fatty acids, add caloric density (energy), act as carriers for flavors, carry fat soluble vitamins, contribute to texture and mouthfeel, and provide heat transfer medium (in frying)

• Fatty acidsShort chain fatty acids are important as odor.longer –chain fatty acids acids are not volatile and do not contribute much to flavor.

• Fatty acids may be saturated or unsaturated.• Fatty acid molecules that are unsaturated

contain what are known as double bond

Characteristics of Fatty Acids

Fatty acid Number of carbon atoms

Melting point (degrees C)

Saturated Fatty Acids

Butyric 4 -7.9

Caproic 6 -3.9

Caprylic 8 16.3

Capric 10 31.3

Lauric 12 44.0

Myristic 14 54.4

Palmitic 16 62.8

Stearic 18 69.6

Arachidic 20 74.4

Unsaturated fatty Acids

Number of carbon atoms

Melting point (degrees C)

Palmitoleic 16 -0.5 to 0.5Oleic 18 13Linoleic 18 -5 to - 12Linolenic 18 -14.5Arachidonic 20 -19.5

Vitamins

1. Fat-soluble vitamins ( vitamin A, D,E,K)2. Water doluble vitamins (vitamin B , C)

Minerals

• Macrominerals (Ca, P, K, Na, Cl, Mg, S)• Microminerals (Cr, Co, Cu, F, I, Fe, Mn, Mo, Ni,

Se, Si, Sn, V, Zn)

Reference

• Parker, R. 2003. Introduction to Food Science. Columbia