Antioxidant profile of red oncom, an Indonesian traditional fermented soyfood

Red oncom is an Indonesian local soyfood traditionally made from by-products of tofu industries through a mould fermentation involving Neurospora sp. Red oncom contains isoflavones and carotenoids, bioactive compounds exerting antioxidant activities. This study aimed to investigate the antioxidant activities of red oncom produced through traditional methods compared to unfermented soybeans and tempeh (or tempe), another Indonesian traditional fermented soyfood. Following red oncom extraction using ethanol 95%, several experiments were conducted, including analysis of isoflavones, carotenoids, total phenolics, total flavonoids and free radical scavenging activity. Antioxidant activity appeared to be significantly higher in red oncom than in unfermented soybeans, but lower in comparison to tempeh (p<0.05). A longer fermentation period was associated with increased antioxidant activities in red oncom along with decay-related organoleptic issues appearing at day-4. Interestingly, antioxidant activities were found to be stronger on the mouldy surface of red oncom compared to its inner side, mainly due to the presence of moulds biosynthesizing carotenoids and hydrolyzing isoflavone glucosides into aglycones. Thus, it was suggested that the potential antioxidative properties of red oncom could support its development as a functional food.