Chemical composition of cow's milk and the factors which it depends on

U radu je prikazan kemijski sastav kravljeg mlijeka i čimbenici o kojima on ovisi. Mlijeko sadrži niz kemijskih sastojaka, pa se u praksi koriste uobičajeni podatci o količini mliječne masti, proteina i mliječnog šećera (laktoza). Kravlje mlijeko u prosjeku sadrži ~3,5% proteina, ~3,7% mliječne masti, te ~4,8% laktoze. S prehrambene strane mliječna mast je glavni energetski sastojak mlijeka i odgovorna je za fizikalna (gustoća, viskoznost) i organoleptička svojstva (miris, boja, konzistencija, okus) mlijeka i mliječnih proizvoda te tehnološke karakteristike. Mliječna mast sastoji se od velikog broja različitih masnih kiselina koje potječu iz dva izvora, jedan dio nastaje de novo sintezom u vimenu, dok drugi dio potječe iz apsorbiranog crijevnog sadržaja. U mlijeku je identificirano više od 200 različitih proteina. Jednoj skupini proteina pripadaju kazeini (oko 80%) koji se acidifikacijom mlijeka precipitiraju iz otopine. Proteini koji ostaju topljivi u tim uvjetima reakcije su skupina sirutkinih ili serum proteina. Laktoza ili mliječni šećer glavni je disaharid mlijeka koji se sastoji od molekule glukoze i galaktoze. Nalazi se samo u mlijeku i jedini je ugljikohidrat mlijeka. Količina pojedinih sastojaka nije stalna i mijenja se pod utjecajem različitih čimbenika: pasmine i zdravstvenog stanja muznih životinja, stadija i redoslijeda laktacije, načina i vrste hranidbe, vrsti mužnje, broju mužnje, sezoni, te o individualnim karakteristikama jedinke (dob, tjelesna masa, zdravstveno stanje i slično). Također valja istaknuti da je u mlijeku najviše promjenjiv udio mliječne masti, a najmanje udio laktoze. Cilj ovoga rada je obraditi kemijski sastav mlijeka i utjecaj navedenih čimbenika na proizvodnju i kemijski sastav mlijeka.The thesis deals with and explains in detail the chemical composition of cow's milk, as well as the factors which it depends on. Milk contains a number of chemical components, so the usual data on the amount of milk fat, protein and milk sugar (lactose) are used in practice. Cow’s milk contains ~3.5% of protein, ~3.7% of milk fat and ~4.8% of lactose. From the nutritional side, milk fat is the main ingredient of milk and is responsible for physical and organoleptic properties (smell, colour, consistency, taste) of milk and dairy products, and is responsible for technological characteristics. Milk fat is comprised of a large number of different fat acids which derive from two sources: one part is created through de novo synthesis in the udder, while the other part derives from the absorbed bowel contents. More than 200 different proteins have been identified in milk. Casein (around 80%), which is precipitated from the solution through acidification, belongs to one protein group. The proteins that remain soluble in those conditions are reactions of whey or serum protein groups. Lactose or milk sugar is the main milk disaccharide which is comprised of a glucose and galactose molecule. It can be found only in milk and is the sole carbohydrate in milk. The amount of the individual components is not constant and changes due to different factors: the breed and health of dairy animals, the sequence and stage of lactation, the type and manner of nutrition, the type of milking, the number of milking, the season, and the individual characteristics of the specimen (age, body mass, health, etc.). It should also be pointed out that the amount of milk fat is the most changeable in milk, whereas the amount of lactose is the least changeable