EFFECT OF TEMPERATURE AND RATE OF ACIDIFICATION ON THE RHEOLOGICAL PROPERTIES OF ACID SKIM MILK GELS

Acid skim milk gels were formed by acidifying milk samples to pH 4.6 at different rates (1-7 h) and at different temperatures (25-40C). At each temperature, the stiffness (storage modulus or G') of the gel increased with increasing acidification time up to 3 h, with smaller changes at longer acidification times. The tan delta of the set gels was independent of the acidification temperature, but decreased markedly with increasing acidification time. The yield stress and yield strain of the acid gels decreased with increasing acidification time. Acidification temperature generally decreased the yield stress and yield strain, although a different behavior was observed at 25C (for yield stress) and 40C (for yield strain). These results are related to changes in the casein micelles on acidification, and the effects of temperature and rate of acidification on these changes.