Growth And Metabolic Interaction Of Lactobacillus Casei Zhang And Bifidobacterium Animalis Subsp.lactis V9 In Yoghurt Fermentation

Milk fermented with probiotics is an ideal carrier to deliver probiotics to human gastrointestinal tract,and is an important application form of probiotics in the field of functional food.However,the growth and metabolic mechanisms of probiotics during milk fermentation are not yet clear.In this study,the growth and metabolic interactions of Lactobacillus casei Zhang and Bifidobacterium lactobacillus V9 during yoghurt fermentation and storage were studied.Main results are as follows:(1)Based on liquid chromatography-mass spectrometry(LC-MS),the growth interaction of Lactobacillus casei Zhang and Bifidobacterium lactis V9 during fermentation at 37? and 42? and its potential metabolic mechanism were studied.When Lactobacillus casei Zhang and Bifidobacterium lactobacillus V9 fermented with starter culture,respectively,comparing with fermentation at 42 ?,37 ?was more beneficial to the growth of Lactobacillus casei Zhang(P<0.05)and the viable cell density at the end of fermentation can increase to 2.65±0.07×108CFU/mL;however,the different fermentation temperatures had no effects on the growth of Bifidobacterium lactobacillus V9.When two probiotics(Zhang and V9)fermented with starter cultures together,Lactobacillus casei Zhang significantly promoted the growth of Bifidobacterium lactobacillus V9(P<0.05);at 37? and 42?,the viable cell density of V9 increased by 64%and 104%,respectively.Through the enriched metabolic pathway analysis,the possible metabolic mechanisms for the rapid growth of Lactobacillus casei Zhang at 37? were the up-regulations of pyruvate metabolism,alcohol degradation and fatty acid synthesis and the down-regulation of glycolysis,arginine and proline metabolism and branched fatty acid oxidation.When the two probiotics(Zhang and V9)co-fermented with starter culture together,Lactobacillus casei Zhang may promote the rapid growth of Bifidobacterium lactobacillus V9 through up-regulating lactose degradation,pyruvate metabolism and vitamin metabolism.(2)When Lactobacillus casei Zhang co-fermented with starter culture,dynamic changes of key volatile metabolites during fermentation at 37? and storage at 4?(14d)were studied by gas chromatography-mass spectrometry(GC-MS).The results showed that acetyl butyl ketone,2-pentanone and heptanol only appeared in the storage stage;octanol and 2-heptanone appeared in the initial and storage stage of fermentation;octanol,caproic acid,decanoic acid and 2,3-butanedione existed in the curd point,fermentation termination and storage period;and acetaldehyde was the key feature from the fermentation termination to the first day of storage.The addition of Lactobacillus casei Zhang can promote the production of diacetyl and make the fermented milk taste better.Through studying the growth and metabolic interactions of Zhang and V9 during yoghurt fermentation and storage,this work provides a detailed insight into growth and metabolic changes during probiotics fermentation and these results can be used for the development of multi-probiotics cultures and probiotic yoghurt.