Antiradical and tea polyphenol-stabilizing ability of functional fermented soymilk–tea beverage

This study examined the potential of two-step fermentation to preserve TPs in functional soy–tea beverage. Fermented soymilk–tea (FST) was produced by culturing Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus and Bifidobacterium longum in soymilk supplemented with tea extract (TE). Total phenolic content (TPC) and anti-radical activities were determined for FSTs and fermented soymilk (FS). A HPLC method was employed to quantify nine major tea phenolics in FST products. TPC was significantly higher (p < 0.05) in FST than FS, in the order of green tea > oolong tea > black tea > soymilk. The FSTs were effective at scavenging DPPH-radical rather than hydroxyl radical. Optimal pH to stabilize TPs in SMT was ca. 5.7, which reduced total TP loss by ca. 40% compared with that obtained from products with TE supplemented at the beginning of fermentation. A gradual decrease in TPs was observed during storage (4 °C), with more than half of total TPs remained in FST after 8 weeks.