A Preliminary Study Of Co-fermentation Of Soybean-based Plant Milk Yogurt By Mixed-culture With Several Probiotics

Health and ethical issues impacted positive growth of milk alternatives.Plant-based milk alternatives became more and more diverse,such as yogurts and butters.It has already taken 10-20%European and American milk market share.With high protein content and good nutrition,soybean is also a very productive and cheap material in China.And soymilk is a popular drink with a long history in our country.So it is the main and popular plant-based milk alternative.Soybean plant-based yogurts are just unfolding products in china.The main problems are:selection of probiotics and adaptable fermentation strains,and good stability,texture and flavor of final products etc.Firstly we selected 6 probiotic strains,which are edible strains according to our country’s regulation.Then we tested their fermentation and probiotics characteristics,including antibiotic resistance,inhibition of pathogens and survival in simulated gastrointestinal digestion.In order to improve the flavor and stability of soybean-based plant yogurt,the optimal strain combination formula was determined by single and mixed fermentation.The optimal process parameters of soybean-based plant yogurt were determined by one-factor experiment and Response Surface Methodology.Then the dynamic change during 16days shelf life was studied.The main research results are as follows:1.Probiotic properties of 6 standard strains:Lactobacillus rhamnosus ATCC7469,L.Switzerland CICC 6032,L.plantarum GIMI 140,L.acidophilus GDMCC1.412,L.reuteri GDMCC 1.614,Streptococcus thermophilus IFFI 6038.It all show inhibition effects of 5 pathogens as Salmonella enterica ATCC 13311,Enterobacter sakazakii ATCC 29544,Staphylococcus aureus ATCC 27217,Listeria monocytogenes ATCC 19111,and Escherichia coli ATCC 29522.None of the six probiotics strains was resistant to common antibiotics like erythromycin,ampicillin,cefazolin and chloramphenicol.6 strains show good survival rate in p H 3.0 simulated gastric acid for 4h,and 6h in simulated intestinal fluid except Str.thermophilus IFFI 6038,with survival vial cell count more than 10~6CFU/m L.2.Study on probiotic mixed fermentation soy-based plant yogurt:L.rhamnosus,L.Switzerland,L.plantarum,Str.thermophilus,these four probiotics grow well in pure soybean milk with a nice cord.While L.acidophilus and L.reuteri can not form a nice curd in pure soybean milk with poor acid-production.Using those four strains with good acid producing probiotics for mixed fermentation,the optimal strain combination formula is:Str.thermophilus:L.rhamnosus:L.switzerland CICC6032:L.plantarum=3:1:1:1.3.Process parameters optimization for soybean-based plant milk yogurt:The optimal ratio of fermentation parameters is:water-bean ratio 6.1:1,white granulated sugar addition amount 10.1%,and the inoculum amount 2.1%.Under this optimal condition,the acidity of soybean-based plant yogurt is 83.33 T,and the sensory score is 85.8 points.4.Dynamic changes during the preservation of soybean-based plant yogurt:4℃under refrigeration conditions,the product shows good stability.None of coliforms,mold and yeast were detected.Although vial lactic acid bacteria gradually reduced,it still higher than 10~6CFU/m L the requirement in GB 19302-2010.The shelf life of this product should be within 16d under refrigeration condition to avoid too acid to affect taste.In summary,4 suitable probiotics strains were selected for soybean-based plant milk yogurt from 6 strains.Best mixing ratio of those 4 strains and the optimal parameters of fermentation were determined to achieve the best flavor and texture of the product.The final product showed good stability and food safety within a 9d shelf life.