Preparation And Antioxidant Activity Of Soy Milk Yogurt And Grape Polyphenols Yogurt

In the paper, we campared the differences of nutrition, flavor compounds andantioxidant activity between soy milk yogurt and milk yogurt, then optimized thefermentation conditions and formula of soy milk yogurt; prepared grape polyphenolsyogurt, and studied antioxidant activity of grape polyphenols yogurt, the results wereas follows:Streptococcus thermophilus and Lactobacillus bulgaricus were used as starter culturesto prepare soy milk yogurt, and milk yogurt was used to be a control. The optimumproportion of pure soy milk and recombined milk prepared soy milk yogurt was6:4bytaking curd acidity and status as evaluation index. It was found that compare with milkyogurt, soy milk yogurt had lower lactic acid bacteria number, and its water holdingcapacity, protein content were higher. Contents of essential amino acids (Isoleucine,Histidine and Arginine) and non-essential amino acids (Aspartic acid, Glycine, Alanine andHomocysteine) were all significantly higher than those of milk yogurt. Twenty six andtwenty five volatile components were detected out in soy milk yogurt and milk yogurt,mainly including: ketones, acids, aldehydes, alcohols, and a small amount of esters, besides2-pentyl furan was detected out in soy milk yogurt but not in milk yogurt. Sensoryevaluation revealed that sensory texture score of soy milk yogurt was quite similar to thatof milk yogurt, and its sensory appearance, flavor and overall acceptability scores werelower than those of milk yogurt.The total antioxidant capacity, DPPH· and·OH radical and ferrous ionchelating ability of soy milk yogurt all enhanced with the increasing of the yogurtconcentration. When the concentration of soy milk yogurt was50g/L, the totalantioxidant capacity was52.216mmol/L (α-tocopherol equivalents), thescavenging rate of·OH and DPPH· and ferrous ion chelating ability were36.4%,45.9%and63.7%, respectively. When the same concentration of yogurt, the totalantioxidant capacity, DPPH· and·OH radical and ferrous ion chelating ability ofsoy milk yogurt were all higher than those of milk yogurt.Domestications on Streptococcus thermophilus, Lactobacillus bulgaricus andBifidobacterium adolescentis were took ty increasing soy milk content of the yogurt base,then the domesticated bacterials were used to prepare soy milk yogurt. The optimumfermentation conditions of yogurt were as follows: the volume ratio of Streptococcusthermophilus, Lactobacillus bulgaricus and Bifidobacterium adolescentis domesticated was 1:2:2, sucrose3%, honey4%, sodium caseinate1%, inoculum5%, fermentationtemperature42℃, culture time6h. Under this condition, the sensory score of soy milkyogurt was8.9. During sixteen days of refrigerated storage, the number of lactic acidbacteria, contents of protein and fat, the titration acidity of soy-honey yoghurt had adecrease trend, but the syneresis increased.0-0.075%grape polyphenols had no effects basically on Streptococcus thermophilusand Lactobacillus bulgaricus according to the series of exoperiments of growth curve. Theoptimum fermentation conditions of grape polyphenols yogurt were as follows: thecontents of grape polyphenols, sugar and sodium caseinate were0.04%,6.3%and0.5%,respectively. The quantity of inoculation was4.2%, the fermented temperature was42℃, and the fermented time was5h. With this understanding, the sensory score of grapepolyphenols yogurt was9.0. During refrigerated storage, the pH, the number of lactic acidbacteria, contents of protein and fat of grape polyphenols yoghurt decreased, but thesyneresis increased.The reduction capability, the scavenging rate of DPPH·,·OH and O2ˉ· radical andferrous ion chelating ability of grape polyphenols yoghurt increased with the inceased ofyogurt concentration. At the same content of grape polyphenols, the scavenging rateof DPPH·, O2ˉ· radical and ferrous ion chelating ability of grape polyphenols yoghurtwere higher than those of grape polyphenols. The reduction capability and the scavengingrate of·OH radical of grape polyphenols yoghurt were higher than those of grapepolyphenols when the content of grape polyphenols was between0.01-0.04%.