Effects of Germination and Rhizopus oligosporus Fermentation on Phenolics and Peptides in Four Legumes
Main Article Content
Abstract
Legumes are abundant in nutrients, and their phenolic and peptide contents can be enhanced through germination and fermentation. However, research on the effects of these combined conditions is still limited. Thus, this study aims to evaluate the effects of germination of soybean, mung bean, red bean, and tiger-striped peanut at root lengths of 0.2 and 1.0 cm, and the fermentation of each germinated legume with Rhizopus oligosporus (germinated-legume tempeh), on their bioactive compounds and antioxidant activities. The results showed that the Total Phenolic Content (TPC) and Total Flavonoid Content (TFC) increased as the germination period increased, with tiger-striped peanuts germinated to a root length of 1.0 cm exhibiting the highest TPC and TFC, at 3.53 mg GAE/g DW and 43.75 mg QE/g DW, respectively. In contrast, germination resulted in decreased Total Protein Content (TPRC) and Total Peptide Content (TPEC) compared with the control, except for the TPRC of red bean and the TPEC of soybean (p-value < 0.05). Antioxidant activities measured by DPPH and ABTS assays tended to increase during germination compared with the control, except in tiger-striped peanuts. The antioxidant activity measured by ABTS was correlated with the bioactive compound contents, particularly peptides (r = 0.909, p-value < 0.01). For the germinated-legume tempeh produced from legumes with a root length of 1.0 cm, fermentation increased the TPC, except in germinated red bean tempeh (p-value < 0.05), with germinated tiger-striped peanut tempeh showing the highest TPC at 7.60 mg GAE/g DW (p-value < 0.05). Fermentation also increased the TPEC, with germinated soybean tempeh showing the highest TPEC at 281.23 mg BSA/g DW (p-value < 0.05). However, fermentation caused decreases in the TFC and TPRC compared with the control (p-value < 0.05), while increasing antioxidant activities measured by DPPH and ABTS assays, except in germinated red bean tempeh (p-value < 0.05). This study demonstrates that germination and fermentation can enhance phenolic and peptide contents, particularly in tiger-striped peanuts and soybeans, increasing their potential for application in the development of health-promoting food products.
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