Protein is an essential nutritional supplement of food that contain may elements of Amino acid
CHAPTER ONE1.1
INTRODUCTION
Milk is one of the most nutritious foods. It is rich in high quality protein providing all tenessential amino acids. It contributes to total daily energy intake, as well as essential fatty acids,immunoglobulins, and other micronutrients. Cow’s milk is the predominant type in severalcountries, although goat, buffalo, sheep, and camel milks are also consumed. Milk is alsoconsumed in fermented forms such as cheese, yogurt, kefir, and buttermilk, and as butter.Commercially available milk can be classified into two major groups: liquid milk and dried orpowdered milk.Proteins are the essential agents of biological function, and amino acids are the building blocksof proteins. The diversity of the thousands of proteins found in nature arises from the commonlyoccurring 20 amino acids. Proteins are polymers of amino acids, with each amino acid residuejoined to its neighbor by a specific type of covalent bond. Proteins can be broken down(hydrolyzed) to their constituent amino acids the free amino acids derived from them. Of theover 300 naturally occurring amino acids, 20 constitute the monomer units of proteins. All 20amino acids are biologically essential. Humans can synthesize 12 (nutritionally nonessential) ofthe 20 common amino acids from the amphibolic intermediates of glycolysis and of the citricacid cycle. Of the 12 nutritionally nonessential amino acids, nine are formed from amphibolicintermediates and three (cysteine, tyrosine and hydroxylysine) from nutritionally essential aminoacids. Proteins are the most abundant organic molecules in animals, playing important roles in allaspects of cell structure and function. Proteins are biopolymers of amino acids, so namedbecause the amino group is bonded to the carbon atom, next to the carbonyl group. The physicaland chemical properties of a protein are determined by its constituent amino acids. Theindividual amino acid subunits are joined by amide linkages called peptide bonds. Protein is oneof the nutrients along with carbohydrate, fat, vitamins, minerals, and water. The source of all ofthese nutrients is good. Some foods contain much higher amounts of specific nutrients than
