Comparison of ultra high pressure homogenization and conventional thermal treatments on the microbiological, physical and chemical quality of soymilk

Abstract

The effect of ultra high pressure homogenization (UHPH) at 200 and 300MPa in combination with different inlet temperatures (55, 65 and 75°C) on soymilk was studied. UHPH-treated soymilk was compared with the base product (untreated), with pasteurized (95°C for 30s) and with ultra high temperature (UHT; 142°C for 6s) treated soymilks. Microbiological (total aerobic meshophilic bacteria, aerobic spores, and Bacillus cereus), physical (dispersion stability and particle size distribution) and chemical (lipoxygenase activity, hydroperoxide index and trypsin inhibitor activity) parameters of special relevance in soymilk were studied. Microbiological results showed that pressure and inlet temperature combination had a significant impact on the lethal effect of UHPH treatment. While most of UHPH treatments applied produced high quality of soymilks better than that pasteurized, the combination of 300MPa and 75°C produced a commercially sterile soymilk. UHPH treatments caused a significant decrease in particle size resulting in a high physical stability of samples compared with conventional heat treatments. UHPH treatment produced lower values of hydroperoxide index than heat treated soymilks although trypsin inhibitor activity was lower in UHT-treated products.