EFFECTS OF AGING OF RAW-MILK ON SOME STRUCTURAL-PROPERTIES OF NATIVE CASEIN MICELLES

The effects of ageing of raw milk were investigated by following the a ctual Ca2+-activity and physico-chemical properties of casein micelles , namely, the average particle size, surface hydrophobicity, and renne ting properties as well as the release of glycosylated and non-glycosy lated caseinomacropeptide. Skimmed raw milk was stored at 4 degrees C for 1 week in the absence and presence of various antimicrobial agents . Proteinase inhibitors' efficiently prevented destabilisation and mol ecular dissociation of casein micelles by indigenous and bacterial enz ymes. The non-enzymic ageing of micelles must also be taken into accou nt. It is characterized by a limited incorporation of ionic calcium in to the micelle followed by an increase in pH-value, micellar voluminos ity and particle size along with a decrease in the overall surface hyd rophobicity of the casein micelles. Enzymic ageing affected the functi onal role of micellar kappa-casein in the primary phase of renneting, whereas the non-enzymic process did not affect the release of CMP duri ng 1 week of storage.