Study On Production Of Soybean Whey-yogurt Rich With Isoflavone Aglycones

Soybean whey is a rich by-product of the tofu manufacturing industries. Soybean wastesof soaking water and soybean whey comprised40%soybean isoflavones. It occurred as themajor proportion of conjugated glycosides (97%~98%of total isoflavones) and less level ofaglycones (2%~3%of total isoflavones). This study adopted lactobacillus to enrich theconcentration of isoflavone aglycones of soybean whey and improved the biological activityof isoflavones, by carrying out systematic research on the isoflavones biotransformationduring the fermented process. Meanwhile, this study provided process parameters andtheoretical basis for the production of functional soybean whey-yogurt, which will explorenew ideas and approaches for utilization of soybean whey.In this study, the nutritional content of soybean whey was detected, and then animproved method of HPLC method for the determination of soybean isoflavone in soybeanwhey was established. Moreover, this study tested and verified the impacts of growthproperties, isoflavones content, β-glucosidase activity in soybean whey fermented by pure andmixed cultures of Lactobacillus plantarum, Pediococcus pentosaceus and Leuconostocmesenteroides. Additionally, the effects of milk powder and sugar supplement in soybeanwhey affected isoflavones concentrations were also investigated. Effects of several singlefactors on soybean isoflavone aglycones concentration were detected. The method of responsesurface analysis was adopted to obtain the optimum technological conditions of makingsoybean whey-yogurt rich with isoflavone aglycones. The stability and quality of the soybeanwhey-yogurt during storage were analyzed. The conclusions were as follows:Soybean whey was shown to be relatively good growth media for lactobacillus. Theaverage composition of the soybean whey was the following (g·100g-1): moisture,97.2;sugars,4.3; protein0.21; fat,0.18; ash,0.46. Soybean whey contained relatively abundant ofcalcium, ferrum, zinc and magnesium, especially ferrum. The organic acid played animportant role in the flavor of soybean whey and the highest content of organic was tartaric(8.02mg·L-1), followed by fumaric acid (5.23mg·L-1). The major components of isoflavones in soybean whey were daidzin25.64mg·L-1, genistin48.12mg·L-1, daidzein0.37mg·L-1,genistein1.17mg·L-1. The content of isoflavone glycosides including daidzin and genistinwas97.95%while it was only2.05%for aglycones including daidzein and genistein.Lactobacillus plantarum, Pediococcus pentosaceus and Leuconostoc mesenteroides allcan convert isoflavone glycosides to aglycones. There were significant increases anddecreases (p<0.05) in the concentration of isoflavone aglycones (from1.54mg·L-1to13.85~19.40mg·L-1) and isoflavone glycosides (from73.76mg·L-1to43.75~46.67mg·L-1)respectively after12h of incubation at37°C with7.0log CFU·mL-1inoculation in thefermented soybean whey. Meanwhile, there was a notable growth in the β-glucosidase activity(from0.042~0.106IU·mL-1to0.131~0.144IU·mL-1), converting the isoflavone glycosides totheir bioactive aglycone forms. Among the single cultures, Pediococcus pentosaceusconducted the best effect on the hydrolysis of isoflavone glycosides to isoflavone aglycones.Moreover, the mixed cultures can improve conversion effects. During6~18h fermentationwith mixed cultures, isoflavone aglycones significantly increased (p<0.05) from7.18~12.38mg·L-1to18.44~21.47mg·L-1, which were higher than that in the single culture from5.04~6.48mg·L-1to15.99~20.56mg·L-1.The content of isoflavone aglycones with the mixedcultures of Lactobacillus plantarum and Pediococcus pentosaceus was21.47mg·L-1whichwere higher than any other cultures.The isoflavone had a significant increase with the addition of milk powder and sugar(p<0.05). Fermented glucose-soybean whey displayed the hightest isoflavone aglycones,followed by the addition of fructose, sucrose and lactose. Glucose-soybean whey fermentedwith the mixed culture of Lactobacillus plantarum and Pediococcus pentosaceus showed thehighest aglycones concentration.The optimum fermentation condition for the preparation of soybean whey-yogurt withisoflavone aglycones fermented by Lactobacillus plantarum and Pediococcus pentosaceus(V/V1:2) were that59%inoculation,7%milk powder and1.98%glucose. The manifestedtest demonstrated that the concentration of isoflavone aglycone was31.31mg·L-1. Comparedwith the unfermented soybean whey the concentration of isoflavone aglycone increased29.77mg·L-1.The addition of stabilizer can improve the stability of soybean whey-yogurt. The best stabilizer mixtures were that0.36%pectin and0.2%carrageenan. During storage, thelactobacillus population and pH value of soybean whey-yogurt exhibited slightly decrease.The concentration of daidzin and genistin decresed slightly，while the concentration ofdaidzein and genistein showed no significant changes. Fermented soybean whey-yogurtappeared delicate organization, good characters, no water stratification and beany flavor, but aslight of soymilk flavor and a little unknown odor. The senses began to change significantlyafter six days storage, and it performed different degrees of abnormalities after nine daysstorage.