Effects of applying Lactobacillus helveticus H9 as adjunct starter culture in yogurt fermentation and storage.

Lactobacillus helveticus H9 is a probiotic bacterium originating from traditional Tibetan kurut. It has high angiotensin-converting enzyme-inhibitory (ACEI) and antihypertensive activities. We aimed to evaluate the effects of L. helveticus H9 supplementation in yogurt fermentation and storage. We monitored changes of multiple parameters over 28 d of storage at 4°C; namely, pH, titratable acidity, free amino groups, ACEI activity, physical properties, volatile flavor compounds, and sensory quality. Supplementation of L. helveticus H9 enhanced fermented milk acidification and proteolysis, resulting in a shorter fermentation time. The H9 treatment significantly increased the ACEI activity of the fermented milks. Fifteen key volatile flavors were detected by solid-phase microextraction-gas chromatography-mass spectrometry across all samples. More alcohols, aldehydes, and nitrogenous compounds, especially acetoin and benzaldehyde, were detected in the H9-supplemented fermented milks. The human sensory scores for flavor and texture, but not appearance, were lower for the H9-supplemented fermented milks, particularly beyond 2 wk of cold storage. Our results will be of interest to the dairy industry for developing novel functional dairy products.