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.