The enhancement of bioactive peptides, dietary polyphenols and antioxidant activity in Rhizopus Oligosporus fermented soybean tempeh through protein hydrolysis [pdf]

Background.There is a growing interest in harnessing bioactive peptides derived from food-grade raw materials, especially for the development of functional foods.Tempeh milk protein hydrolysates (TMPHs) are interesting sources of bioactive peptides.In the current study, TMPHs were characterized by their bioactive peptides, dietary polyphenols and antioxidant activity.Material and methods.TMPHs were made from Rhizopus oligosporus fermented tempeh with fermentation times of 0, 1, 2, 3 and 4 days, designated as TMPH0, TMPH1, TMPH2, TMPH3 and TMPH4, respectively.The morphological appearance of tempeh was examined by scanning electron microscopy.The analyzed characteristics of TMPHs were physicochemical properties, total soluble proteins (TSP), trichloroacetic acid (TCA)-soluble peptides, bioactive peptides, antioxidant activity, total phenolic compounds (TPCs) and total flavonoid compounds (TFCs).Results.The morphological appearance and microstructure of tempeh with varied fermentation times were different under SEM due to the growth of R. oligosporus.The pH of TMPHs remained constant at 7 for samples with fermentation times of 0, 1 and 2 days and continuously decreased for those fermented for 3 and 4 days.However, total acidity continuously increased from the first day of fermentation.TMPH3 had the highest level of total soluble proteins and trichloroacetic acid (TCA)-soluble peptides.SDS-PAGE analysis demonstrated that TMPHs consist of various protein fractions with large molecular weights from 25 kDa and with lower molecular weights.Their SDS-PAGE patterns were different, indicating protein alteration during fermentation.In DPPH and ABTS assays, TMPH3 exhibited the strongest antioxidant activity.These results agreed with those from the analysis of total phenolic compounds (TPCs) and total flavonoid compounds (TFCs) showing that TMPH3 had the highest TPC and TFC.