Study On Storage Stability Of Fermented Milk With Probiotics Lactobacillus Helveticus H9

Lactobacillus(L.)helveticus H9 is a probiotic bacterium originated from traditional Tibetan kurut.It has high angiotensin-converting enzyme(ACE)inhibitory and antihypertensive activities in fermented milk.This study aimed to evaluate the effects L.helveticus H9 supplementation in storage.The mixed fermented milks were made by four different inoculum of L.helveticus H9(1×10~6,2×10~6,5×10~6,1×10~7CFU/g)and 0.003%commercial culture starter YF-L904.We monitored changes of multiple parameters over 28-day storage at 4?,namely p H,titration acidity,free amino nitrogen,ACE-inhibitory activity,physical properties,volatile flavor compounds,and sensory quality.(1)The supplementation of L.helveticus H9 enhanced fermented milk acidification and proteolysis,resulting in a shorter fermentation time.With the addition of L.helveticus H9 had shortest fermentation time(3.75±0.01h)at an inoculum concentration of 1×10~7CFU/g.Both the acetate(0.14±0.01 to0.17±0.02g/L)and citrate(0.24±0.01 to 0.30±0.02g/L)concentrations remained stable throughout the storage period(P>0.05)when a high inoculum concentration of L.helveticus H9(1×10~7CFU/g)was used.(2)The H9-treatment significantly increased the ACE-inhibitory activity of fermented milk(P<0.05),especially at an inoculum level of 1×10~7CFU/g.The highest ACE-inhibitory activity(78.28±1.54%)was detected after 14 days of storage.The texture of fermented milk in each group did not change significantly during the storage period.Fifteen key volatile flavors were detected by solid phase microextraction gas chromatography mass spectrometry(SPME-GC-MS)across all samples.More alcohols,aldehydes,and nitrogenous compounds were detected in the H9-supplemented fermented milks.(3)The apparent score was negatively correlated with the ability of syneresis(r=-0.52)by correlation analysis;the flavor score was positively associated with1-pentanol,heptanal,pentanal,but not significant;and the texture score had no significant correlation with texture parameters.And sensory evaluation results showed that L.helveticus H9 did not affect the quality of fermented milk.Our work is of interest to the dairy industry for developing novel functional dairy products.