Ultrasound and enzymatic treatments improve protein content and functional properties of soybean tempe protein isolate

Abstract Tempe is a fermented soybean from Indonesia with high protein and nutrient bioavailability, making it a promising raw material for producing protein isolates. Soybean germination prior to fermentation has been shown to improve protein quality and affect its functional properties. However, tempe protein isolate (TPI) produced using conventional extraction methods typically contains only 70–80% protein, which is not by the minimum standard of 90% for protein isolates. This study aimed to develop an improved extraction method for producing TPI with a minimum of 90% protein content and to compare its physicochemical and functional properties with TPI extracted from conventional methods. The improved extraction process involved disrupting biomass cells using ultrasound treatment and carbohydrase enzyme (Viscozyme®) hydrolysis. The results showed that the improved method (30 min of sonication combined with 30 FBG Viscozyme per 10 g flour) increased the protein content to 90% and improved protein recovery. It also improved water and oil absorption capacities, emulsion and foam capacity and stability, and altered the microstructure of the TPI. Additionally, the soybean germination process before tempe fermentation significantly improved the TPI's physicochemical and functional properties by promoting the breakdown of non-protein components and supporting new protein synthesis.