In this study, the mean pH values of samples added with apple
juice were lower than those of control samples (Table 1). Supplementation
of soy milk with apple juice provided additional
carbohydrates as energy sources led to increase in the metabolic
activity of L. acidophilus which contributed to the decrease of pH.
For each sample group, there was no significant difference between
pH values determined at different storage periods. The
variations in pH and titratable acidity were slight through the
storage period of 21 days for control and apple juice containing
beverages. Lin, Chiu, and Pan (2004) suggested that slight variations
of pH and titratable acidity values of soy milk beverage
may have been due to the buffering effect of solids such as soy
proteins and sugar.