AN EFFECT OF THE LOW-TEMPERATURE INDUCED PROCESSES OF DISSOCIATION-ASSOCIATION ON THE MOLECULAR-STATE OF CASEIN

Cold-storage of milk at the temperature below 5 degrees C causes parti al dissociation of casein fractions, especially beta-casein from micel les. This phenomenon leads to a decrease of the micellar casein conten t and to changes in micelle size distribution. Decrease of cheese yiel d and changes in functional properties of milk are the technological c onsequences of storage at low temperature. The aim of present study wa s to investigate the possibility of a reversion of changes occurring i n casein micelles due to cooling. Bulk milk was stored at 5 degrees C for up to 48 h, and then equilibrated by stabilization (22 degrees C, 24h) or in thermization conditons (65 degrees C, 15 s). Cold-storage o f milk caused the decrease of large micelle content, the partial disso ciation of individual caseins from micelles (mainly beta-casein-fracti on with the highest hydrophobicity), disturbance of salt system balanc e in milk by decrease of level of calcium and phosphorus bound to mice llar casein and change of ratio of these elements as well as surface h ydrophobicity. Both ways of equilibration caused partially reversion o f changes occurring in milk protein system due to cooling. Thermizatio n led to more complete reversion of changes as compared to stabilizati on.