Dairy Chemistry

MILK COMPOSITION AND ITS PROPERTIESPrepared By MR D.M. NjugunaFor2009 Hygienic milk handling and processing course lecturer Dairy Training Institute

1Reference materials Tetra Pak. Dairy processing handbookNotes from - professor Doug Goff university of Guelph Canada. Peiter W. and Robert J. Dairy chemistry and physicsKenya Bureau of Standard Document , Kenyan standard code of hygienic practice for production handling and distribution of milk and milk products.

Objective Of The Training To provide information for training inProperties and characteristics of good quality milkIntroduction to milk and milk yielding animals.General Composition of milk( emphasis on cattle milk).The Properties of milk .

3Characteristics of good quality milk Wholesome and free from added water or foreign substances Free from drug residuesWhite creamy in colour.Free from foreign smellsLow in bacterial count.It helps your client harvest quality milk

Raw-Whole milk for saleBe obtained from a healthy dairy animalBe free from Colostrum and mastitis.Be free from added water, preservatives or any added substancesHave not less than 3.25 milk fat and 8.5 solids non fatHave a density equivalent to a lactometer 0f 28-32

Tips on how to maintain milk qualityKeep the milk as cool as possible.Do not shake milk excessively Keep milk covered all the timeTransport the milk to the point of sale in the shortest time possible.Protect milk from light and high temperature to avoid spoilage.Do not transport milk together with other goods or passengersTo maintain quality Tips cont..Keep the transport vehicle clean and well maintained.Safely secure the milk cans to avoid spillage and contamination .wear appropriate clean clothing so as to avoid contaminating the milk.Introduction to milk

8Milk yielding animals -Sources of milk

Cow 80% of the worlds milk production.Goat found in the middle east.Sheep also kept in middle east.Buffaloes India , Egypt. Camel- North Eastern Kenya

Legal definition of raw milk.

Milk shall contain not less than 3.25 % milk fat and not less than 8.5 per cent solids non fat. It shall not contain any added water , preservatives , or other added substance,nor shall any proportion of a natural constituent be removed.Cont.

The density of milk at 20 oC shall be within the following range 1.026 1.032 g/ml.The freezing point at.-0.52- (-0.54).

Colostrum milk

The milk secreted for the first few days after parturition is known as colostrum It differs greatly from normal milk in composition and properties,Cont.

Has high content of B-lacto globulin.,Globulin And albumin.Coagulates when heatedContain antibodies which protect the calve from infection.Cont.

Is yellowish to brown-yellow color.Has a peculiar smell and a salty taste.The content of catalase and peroxidase is high.

Value of Milk Composition

Nutritive value of milk.Natures most complete foodUsed in marketing milk

Nutritive Value of Milk

Its natures most compete foodThe cow produces over 70% of the worlds milk.The history of man/cow is prehistoric.-kept for milk and meatMilk has Essential fatty acidsEssential amino acids for growth.

Milk is

Its the first food of the newly born mammal.Its the liquid secreted from the mammary gland of a mammal for the nourishment of their young.A lacteal secretion obtained from milking the healthy udder of a healthy cow, properly kept and fed and obtained not less that 7 days after calving.Factors that affect milk composition

Breed.Stage of lactationAgeFeedsMilking intervalDisease.

Abnormal milkColostrumMilk from diseased udder mastitic milkContaminated milk .ColostrumPhysical identificationComposition high serum proteinsColostrum has brownish-yellow colour, a peculiar smell and a rather salty taste.The content of catalase and peroxidase is high. Four to five days after calving the cow begins to produce milk of normal composition, which can be mixed with other milk.

Changes that occur in milkCreaming of fat and crystallization of part of fat during cooling.Presence of oxygen and nitrogen in milk and loss of carbonChanges due to lightVariation of salt composition and PH with temperatureConEnzymes reactions.LypolysisProteolysisHydrolysisMicrobial changes most conspicuous Temperature effect on milk .Types of milk heat treatment and effect on composition

Composition of milk

As a food it providesEnergyProteinsCalciumPhosphorousVitaminsContains five main componentsWater FatsProteinsMilk carbohydrateMinerals/ash

Other constituentsPigmentsEnzymesVitaminsPhospholipids

Composition of cows milk

Water- 87.5%Fat - 3.7%Protein- 3.4%Lactose-4.8%Minerals-0.7%

Milk nutrients and their role in milk processing

Water- 87.5 %This is the main milkConstituent. The water carries in solution milk sugar, mineral salts and water soluble vitamins. Suspended in milk are fats,casein and certain mineral salts such as calcium phosphates, and magnesium phosphates. A portion of water is bound to lactose, protein and salts.

Contn.Lactose-4.8 %The only carbohydrate of animal origin in human diet.Is a disaccharide-made up of glucose and galactose.-Its split down by the enzyme lactase.There is a relationship between lack of lactase and lactose intolerance.Fermented milk recommended for lactose intolerance people.

Contn.

Milk fat- 3.7 %A source ofEnergyFatty acidsFat soluble vitamins.

Contn.

Energy the oxidation of fat in the body yields nine calories per gram.Fat composition 98-99% triglycerides 1-2 % othersPhospholipidsSteroidsCarotenoidsVitaminsFree fatty acids

Contn.

Milk protein-3.4%Essential to all life processesContain three protein categoriesCaseinAlbuminglobulin

Contn.

Casein 78% of the milk proteins2.6% of the whole milk.Can be separated from milkBy acidBy rennetRennet is used to coagulate milk in cheese making.

Contn.

Other proteinswhey proteinsAlbuminGlobulinAlbumin-10-15%Globulin-2-5%

othersLactose- found in wheyMilk salts.-

Milk enzymes

An enzyme is a biological catalyst.Examples found in milk are;LipasePhosphatasePeroxidase.Important in dairy industry

Milk salts.

Minerals 0.7%Important in human nutrition.They are derivatives ofChloridesPhosphatesCitratesAndCalciumPotassiumSodiumCalcium deficiency leads to rickets in children.

Vitamins in milk

Nutritionally important component in milk.Best known milk vitamins are:AB1B2CDA and D are fat solubleOthers are water soluble.

PHYSICAL PROPERTIES OF MILKAPPEARANCEDENSITYFREEZING POINTPH.

appearanceColor of milkDue to the content of fat,proteins and certain mineralsVaries from white to yellow depending on fat content

Density of milkVaries from :1.026-1.032Milk is denser than water- 1.000

Freezing pointVaries from:-0.54 to (- 59 0 CDepend on the content of LactoseProteinsMineralsA higher concentration result in a lower freezing point.

39PHPH of milk is between 6.6- 6.7Normal milk is slightly acidic

Milk PH and AciditySignificance of milk PHRaw milk- measure of qualityMilk products- monitoring the quality.

PH- landmark PH values for raw milk6.8-6.9 mastitis milk or attempted neutralization with alkali.6.6-6.7 normal PH of milk