Development Of Functional Yoghurt Fermented By Lactobacillus Plantarum B1-6 And Lactobacillus Helveticus MB2-1 With Soy-cow Milk Mixtures

The yoghurt is fermented by plant food-sources and animal food-sources lactic acid bacteria strains with soy-cow milk mixtures.It's a kind of gel products like coagulability yoghurt.Sometimes transglutaminase(TGase)were added to form gel synergistically and sweeteners were added to give a pleasant taste.With the complementarity characteristics of both plant and animal protein,this kind of yoghurt also has white,delicate,elastic flavor just like fresh cheese.The main research and findings were as follows:1.Study on the determination of lactic acid bacteria strains of soy-cow milk and processing technology of the yoghurtThe food-sources LAB strains in our laboratory were screened and we found that Plant lactobacillus B1-6 could grow fast in soy-milk but hard to grow in cow-milk.On the contrary,Lactobacillus helveticus MB2-1 could grow fast in cow-milk but hard to grow in soy-milk.When B1-6 and MB2-1 were inoculated into soy-cow milk mixtures at the same time,they all could grow well.So B1-6 and MB2-1 could be used for making the yoghurt.Some key factors during fermentation process were analyzed through single factor experiment and JMP custom design experiment with acidity,water-holding power and gel strength which were comprehensive evaluation index.The optimum formula of fermentation technology were as follows:the inoculation amount 3.72%,fermentation temperature 37?,the ratio of Bl-6 to MB2-1 1:1,the ratio of water to soybean 9,the ratio of soy-milk to cow-milk 4:6.The response value under the best process parameters were:acidity 77.41 ±5.45°T.water-holding power 75.08%±2.45%,hardness 87.67±4.42g.Verification experiments were carried out under optimum conditions and the results were as follows:acidity 73.4°T,water-holding power 75.44%,hardness 90.38g which were fitting the prediction by JMP.2.Changes in physical properties of the yoghurt during storage processAcidity,pH,viable count of the probiotics,the total colony number,the total number of E.coli bacteria,mold and yeast,water-holding power,texture and sensory evaluation of the fermented yoghurt during different storage time at 4? were analyzed.According to the research,the fermented yoghurt which was stored during 13d keeps good quality,acidity 97.53° T,pH 3.96,viable count of lactobacillus 5.2 × 10~8cfu/g,E.coli bacteria,mold and yeast were all not detected,water-holding power 76.32%,fuzzy mathematic sensory evaluation mark 4.8032(total mark 10),texture factors:hardness 129.45 g,gumminess 105.38 g,cohesiveness 0.81 mJ,resilience 0.48.3.Research on the functional activity of the yoghurtThe changes of the degree of hydrolysis and small peptides contents of the soy-cow milk mixtures and the fermented yoghurt during sequential in vitro digestion were analyzed.Also,ACE-inhibitory activity and anti-oxidative effect of the soy-cow milk mixtures,the fermented yoghurt and their digestions in vitro were studied.The results showed that with the increase of the degree of hydrolysis,small peptides contents also increase gradually.The ACE-inhibitory activity of soy-cow milk mixtures,the fermented yoghurt and their digestions were determined by HPLC.Results showed that unfermented soy-cow milk mixtures had no ACE-inhibitory activity,comparing to its stomach-digestion and gastrointestinal-digestion were 8.52%and 19.56%.The ACE-inhibitory activity of the fermented yoghurt was 48.84%,comparing to its stomach-digestion and gastrointestinal-digestion were 93.30%and 95.35%After fermentation,ferric reducing antioxidant power,reducing power and the DPPH-free radical scavenging activity of the fermented yoghurt were much lower than samples that were digested.The anti-oxidative activity of the fermented yoghurt after digestion had improved dramatically.