Reaction kinetics of heat-induced colour changes in soymilk

Abstract

The kinetics of colour changes in soymilk heated over a wide range of temperatures (80°C–140°C) and times (0–180 min) were studied using both instrumental analysis and sensory evaluation methods. On the basis of the CIELAB uniform colour space, the L*-value decreased following first order kinetics, but unlike cow’s milk, soymilk did not exhibit an initial whitening phenomenon upon heating. The a*-and b*-values increased following zero order kinetics. The reciprocal of percentage reflectance (1/ R) measured at 450 nm increased according to a first order reaction. Chroma ( C*) and hue ( h*) can be described well with zero order reaction kinetics. Sensory evaluation based on a nine-point quality scale showed a linear response between panel score and heating time. Compared with previously reported results for cow’s milk, the changes in the CIELAB values in soymilk due to heat appeared to follow similar patterns, but the reactions were slower and less temperature sensitive.