Antioxidant activity and isoflavone content of overripe Indonesian tempe

Abstract

The germination process and prolonged fermentation have been shown to improve tempe quality. The present study aimed to measure and compare the changes in nutritional and isoflavone content and antioxidant activity of tempe flour due to soybean germination and fermentation time treatments. Soybeans were germinated for 24 hrs before being fermented into fresh and overripe tempe for 2 and 7 days, respectively. Fresh and overripe tempe were dried using a cabinet dryer at 60oC for 8 hrs, then ground and sifted to produce flour. The nutritional contents were determined through proximate analysis, antioxidant activity was measured using the DPPH method, and isoflavone was measured using an HPLC instrument. The germination process and fermentation time were shown not to affect the nutritional contents but affect isoflavone content and IC50 value significantly. Overripe tempe flour made from germinated soybeans had the highest daidzein and genistein isoflavone content, at 343 and 701 µg/g, respectively. However, overripe tempe flour made from non-germinated soybeans has the highest antioxidant capacity, with an IC50 of 1375 ppm. This result showed that to reap the benefits of high antioxidants, tempe fermentation may be prolonged to produce overripe tempe without any requirement to germinate the soybeans beforehand.