Sensory and chemical characteristics of soymilk yogurt with different yogurt cultures

The objective of this study was to develop commercially acceptable soymilk yogurts and determine their sensory and chemical characteristics as affected by using different combinations of lactic acid bacteria. Plain, vanilla, or strawberry flavored soy yogurts were formulated with bland soymilk and 0.15%, 0.3%, or 0.2% yogurt culture, containing Streptococcus thermophilus and Lactobacillus bulgaricus. Descriptive analysis and consumer tests indicated that strawberry soy yogurt had higher intensities of overall flavor and aroma, and was more liked by consumers than the plain and vanilla soy yogurts. Volatile and non-volatile compounds were determined in soy yogurts made with bland soymilk and 0.2%, 0.5%, or 1.0% of yogurt cultures containing different combinations of lactic acid bacteria. The cultures used were a standard culture; containing Streptococcus thermophilus and Lactobacillus bulgaricus (STD), standard culture plus L. acidophilus and Bifidobacteria ssp. (STDAB), or standard culture plus L. lactis (STDL). Dairy yogurts were also made with 2%-fat cow's milk and 1.0% of each of three mentioned starter cultures. Static headspace gas chromatography was used to determine volatiles in soy yogurt samples. High pressure liquid chromatography (HPLC), with UV and RI detectors, was used for the determination of organic acids and sugar, respectively. Sensory descriptive analysis was performed on fresh soy and dairy yogurts with 1.0% level of STD, STDAB, or STDL cultures.;Analyses showed that acetaldehyde and diacetyl were predominant volatiles in soy yogurts. Acetone, ethanol, 2-heptanone, and methanol were also found. The amounts of hexanal found in yogurt samples were lower than the threshold values and did not contribute to distinctive beany flavor in soy yogurts. The STD culture produced higher concentrations of acetaldehyde and diacetyl than the STDAB and STDL cultures in both soy and dairy yogurts. Refrigerated storage at 4°C for up to 60 days did not have major effect on the concentrations of most volatiles in soy yogurts. However, the acetaldehyde declined significantly in dairy yogurt samples after 10 days of storage (P < 0.05). That suggested better flavor stability in soy yogurts than dairy yogurts. Raffinose and stachyose were reduced in soy yogurt samples with STDAB and STDL cultures. Although acetaldehyde and lactic acid were present in higher concentrations in the dairy yogurts, the sensory study indicated that soy yogurts were rated higher in overall flavor, acetaldehyde and lactic acid flavors.