Antioxidant activity of tempe fermented with three different <i>Rhizopus</i> species

Tempe, a traditional Indonesian fermented soy-based food, reportedly has higher antioxidant activity than unfermented soybeans. In 2015, the Codex Alimentarius defined the starters of soybean tempe to be Rhizopus microsporus var. oligosporus, Rhizopus oryzae, and/or Rhizopus stolonifer. Most previous studies have focused only on tempe prepared with R. oligosporus. In this study, we compared the antioxidant activities of tempe fermented with three Rhizopus species and unfermented soybeans using assays for β-carotene bleaching (antioxidant activity), antioxidative potential, and oxidative stabilization. The β-carotene bleaching and antioxidative potential assays indicated that the tempe fermented with R. stolonifer had higher antioxidant activity than the tempe fermented with R. oligosporus and R. oryzae. We speculate that the high antioxidant properties of this product are attributable to the isoflavone aglycones and hydroxylated compounds produced by fermentation.