Department of Food and Nutrition, School of Food Engineering, University of Campinas, Rua Monteiro Lobato, Campinas, SP, 13083-862, Brazil.
Appl Microbiol Biotechnol. 2020 Dec;104(23):10019-10031. doi: 10.1007/s00253-020-10986-1. Epub 2020 Nov 2.
Isoflavones are phenolic secondary metabolites mainly occurring in soy and soybean products. Compared to glycoside forms, isoflavone aglycones present higher biological activities. This study evaluated the potential of microbial and enzymatic treatments in biotransformed isoflavones in their biologically active forms in soymilk. Seven different cultures of lactic acid bacteria and bifidobacteria associated with the action of immobilized tannase enzyme were screened for isoflavone glycoside biotransformation ability. The biotransformed soymilk samples were characterized regarding isoflavone profile, total phenolic content, and in vitro antioxidant activities. All bacterial strains showed a good growth capacity in soymilk matrix and produced β-glucosidase enzyme, which hydrolyzed isoflavone glycosides into aglycones in soymilk after 24 h of fermentation. The microbial fermentation followed by tannase reaction (FT processes) resulted in the highest increase of bioactive aglycones (10.3- to 13.1-fold for daidzein, 10.4- to 12.3-fold for genistein, and 3.8- to 4.7-fold for glycitein), compared to control soymilk. Further, FT processes enhanced the total phenolic content (53-70%) and antioxidant activity by ORAC (69-102%) and FRAP (49-71%) assays of the soymilk matrix. Therefore, the combination of microbial fermentation and tannase treatment is a promising strategy to obtain a fermented soy product rich in bioactive isoflavones with greater health-promoting potential. KEY POINTS: • Bacterial cultures and tannase enzyme displayed isoflavone deglycosylation activity. • The addition of tannase following the fermentation maximized the isoflavone conversion. • Increased isoflavone aglycones contributed to the improved antioxidant activity of soymilk.
异黄酮是主要存在于大豆及其制品中的酚类次生代谢物。与糖苷形式相比，异黄酮苷元具有更高的生物活性。本研究评估了微生物和酶处理在将大豆异黄酮转化为生物活性形式方面的潜力。筛选了 7 种不同的乳酸菌和双歧杆菌培养物，这些培养物与固定化单宁酶一起作用，具有异黄酮糖苷转化能力。对生物转化后的豆浆样品进行了异黄酮谱、总酚含量和体外抗氧化活性的表征。所有细菌菌株在豆浆基质中均表现出良好的生长能力，并产生β-葡萄糖苷酶，该酶在发酵 24 小时后将异黄酮糖苷水解为豆浆中的苷元。微生物发酵后再进行单宁酶反应（FT 工艺）可使生物活性苷元的含量增加最高（大豆苷元增加 10.3-13.1 倍，染料木苷增加 10.4-12.3 倍，黄豆苷元增加 3.8-4.7 倍）与对照豆浆相比。此外，FT 工艺提高了豆浆基质的总酚含量（提高 53-70%）和抗氧化活性（通过 ORAC 测定提高 69-102%，通过 FRAP 测定提高 49-71%）。因此，微生物发酵和单宁酶处理相结合是一种很有前途的策略，可以获得富含生物活性异黄酮的发酵大豆产品，具有更大的促进健康潜力。关键点：• 细菌培养物和单宁酶显示出异黄酮去糖基化活性。• 发酵后添加单宁酶可最大程度地促进异黄酮转化。• 增加的异黄酮苷元有助于提高豆浆的抗氧化活性。
