Research Of Fermented Soy Milk Fortified With C9,t11-conjugated Linoleic Acid By Lactic Acid Bacteria

At present,the food fortified with conjugated linoleic acid(CLA)fermented by lactic acid bacteria(LAB)is still in the research stage,and cow dairy products are the main products.Soybeans are rich in nutrients,protein,linoleic acid(LA),flavonoids and other nutrients.The nutritional value of fermented soy milk(FSM)with abundant active peptides and reduced anti-nutritional factors is improved.Therefore,soymilk can be used as a growth substrate for LAB to produce FSM products fortified with c9,t11-CLA.In addition,thermal processing and the presence of oils will affect the dissociation and association of soy milk particles,which in turn affects the formation of FSM gel network and the texture.However,there are few reports on the effect of LA and heat treatment on soy milk granules and the gel properties of FSM.In this study,by exploring the synthesis of c9,t11-CLA in soy milk fermented with LAB and the characteristics of soymilk under different fermentation conditions,the optimal fermentation conditions of soy milk were determined,and the effects of heat treatment and LA on the particles of soy milk and gel properties of FSM was evaluated.The main contents of this study include: determining the technological conditions of soymilk preparation such as soaking,grinding,filtration and boiling;exploring the properties of FSM and the synthesis of c9,t11-CLA under different fermentation conditions,and determining the storage characteristics of FSM;the effects of thermal processing and LA on the formation of soymilk granules and the texture of FSM were investigated.The results are showing as follows:1.Analysis the quality of soymilk by dynamic light scattering instrument,UV spectrophotometer and other instruments,and determine the pulping process.The results showed that the water absorption rate of soybean increased faster at room temperature than that at 4℃,and the water absorption rate reached 1.33 after soaking for 9 h;the soymilk could reach the highest concentration of soluble solids by refining the soymilk for 15 min;four layers of gauze filter soymilk can effectively reduce the particle size of soymilk;lipoxygenase was completely inactivated when the soymilk was boiled for 6 min,and urease was negative after 9 min.2.The p H,acidity,viable count and c9,t11-CLA content of FSM were measured under different concentrations of soymilk soluble solids,LA concentration and fermentation time.The results showed that the content of c9,t11-CLA in FSM reached the highest content of 838.67 μg/g whenfermentated 72 h with 7°Brix soluble solids concentration,0.1%(v/v)LA concentration and 72 h fermentation time.Under the condition,the total flavonoid content of FSM increased from 3.39 mg RE/g to 4.24 mg RE/g,and the total acidity and total flavonoid content of yogurt milk did not change significantly within 21 days under the condition of refrigeration at 4°C,and the viable cells number was higher than 6 log CFU/m L,c9,t11-CLA content decreased slightly from 838.67 μg/g to 816.33 μg/g.Within 14 days,the texture properties of yogurt,such as firmness,consistency,cohesiveness and viscosity index,were relatively stable.3.The effect of thermal processing and LA on the formation of soymilk granule protein was evaluated by electrophoresis.It was found that thermal processing can dissociate and association protein subunits such as 7S α’,7S α,7S β,γ-conglycinin,soybean agglutinin,trypsin inhibitor,11 S A3 and 11 S acidic and basic subunits in soymilk granules,and LA can accelerate this process.Low concentration of LA under thermal processing can increase the water holding capacity of yogurt and reduce whey precipitation.Through the measurement of the texture of FSM and the observation of the gel network structure,it was found that low concentration of LA acts as an inactive filler in the FSM gel,and the gel network of FSM exhibits a layered structure,which makes the texture is softer,and improving its organoleptic qualities.