EFFECT OF COLD STORAGE AND HEATING OF CAMEL S MILK ON FUNCTIONAL PROPERTIES AND MICROSTRUCTURE IN COMPARISON WITH COWS AND BUFFALO S MILK

The effect of cold storage (4°C/48h.) and heating (85°C/5min.) on some properties of camel s, cow s and buffalo s milks were studied. These included acidity, pH, nitrogen distribution, rennet coagulation time (RCT), surface tension (ST), foam expansion (FE), foam volume stability (FVS), buffer intensity , the electrophoretic properties and microstructure. Cold storage of all milk samples increased acidity, and decreased pH, ST, RCT (except camel s milk) and FE (except cow s milk). No significant effect on CN, NCN and WPN was found. Heating all milk samples increased acidity, casein nitrogen (CN) and RCT (except camel s milk), decreased non-casein nitrogen (NCN), whey protein nitrogen (WPN) and non significant effect on ST. Also, heating decreased only FE of buffalo s milk and increased the others, while FVS of camel s milk was not recorded (after 15 min.). In all cases, buffer intensity curves showed same peaks and were the highest at pH( 7-8 ) and (6.5-7.5) in buffalo s and cow s milk respectively. However, camel s milk had less buffering capacity compared with either buffalo s or cow s milk. Concerning, the electrophoretic patterns, some whey proteins especially p-lactoglobulin (p-Lg) disappeared on heating, whereas cold storage slightly decreased P-casein. In general, camel s milk showed different protein patterns. There was little microstructure difference between raw and cooled (4°C/48h.) camel s, cow s and buffalo s milk; while heat treatment increased the size of casein micelles in all samples.