Impact of different thermal treatments and storage conditions on the stability of soybean byproduct (okara)

Abstract

Okara is the byproduct obtained from tofu or soymilk production process. It has a rich nutritional composition, especially in fibers, proteins and lipids. Stabilization processes are required to assure its efficient and safe use, because there are few studies on okara. The main objective of this study was to evaluate the chemical composition (protein, fiber, lipids, ash and isoflavones), microbiological stability, antioxidant capacity and antinutritional factors in fresh okara stored at 4 and − 18 °C and dried okara (80 °C/5 h and 200 °C/1 h) stored at room temperature for 15 days. Okara showed a rich nutritional composition—ca. 35% of fiber, 30% of protein and 11% of lipids. The okara’s lipid profile showed high and valuable level of PUFA (ca. 56%) followed by MUFA (ca. 21%) and SFA (ca. 23%). The Fresh okara showed the highest antioxidant activity and total phenols, however for isoflavones (genistin, genistein, daidzin, daidzein) the dried okara at 200 °C exhibited higher content compared to dried okara at 80 °C and fresh okara. Okara samples submitted to thermal treatment showed a decrease in antinutritional factors in relation with fresh okara, whereas the treatment of dried okara at 200 °C was the most efficient inducing a decrease of ca. 6 times. In conclusion, the nutritional richness of this byproduct suggests okara as a valuable nutritional ingredient for further inclusion in food and feed, but considering the limited studies carried out to date, further studies are warranted to better stabilize okara.