Abstract:

The volatile components of the soymilk yoghurts fermented by Streptococcus thermophilus plus Lactobacillus bulgaricus (1:1 or 1:2 mixing ratio) or Lactobacillus helveticus (1:1 mixing ratio) were analyzed using headspace solid phase microextraction (SPME) combined with gas chromatograph/mass spectrometer (GC-MS) and sensory evaluation was conducted for these yoghurt samples. The effects of different species of Lactobacillu and mixing ratio for Lactobacillu and Streptococcus thermophilus on the volatile components of soymilk yoghurts were explored. In comparison with pre-fermented soymilk, all the three soymilk yoghurts showed significantly higher contents of ketones and acids but significantly lower contents of aldehydes and alcohols. The contents of the key flavor compounds found in all of them were different. The results of evaluation were consistent with those of aroma composition analysis. The soymilk yoghurt produced with Streptococcus thermophilus plus Lactobacillus bulgaricus at 1:1 mixing ratio had strong aroma and high acidity. Therefore, an excellent fermentation starter has been found for the production of soymilk yoghurt through this study.

Key words: lactic acid bacteria, soymilk yoghurt, SPME, GC-MS, aroma