Ultrasound-Assisted Enzymatic Extraction and Physicochemical Properties of Soluble Dietary Fiber from Soy Sauce Residue

There are millions of tons of fresh soy sauce residue (SSR) by-products created by China's soy sauce industry every year. Most of the SSR is directly discarded; this not only wastes resources, but also pollutes the environment. As it is rich in dietary fiber, which is beneficial to human health, skimmed SSR was used as a raw material to obtain soluble dietary fiber (SDF) in this study. Firstly, the process of ultrasonic-assisted enzymatic extraction of SDF was optimized through single factor experiments and a response surface test. The extraction rate of the SDF from SSR reached 76.8 +/- 0.8% under the optimum extracting conditions of a cellulase/hemicellulase (w/w) 1/1 mixture, an enzyme addition amount of 5.7%, a material-liquid ratio (w/v) of 1/20 g/mL, and a reaction time of 30 min. Then, the physicochemical properties of the SDF extracted using enzymatic and chemical methods were compared; we found that the SDF obtained through ultrasound-assisted enzymatic extraction had a much better appearance and physicochemical properties than that extracted by acid or alkali, with a lighter color, higher extraction rate, higher water-holding capacity, higher oil-holding capacity, higher swelling capacity, and solubility. The microstructure was more uniform and porous. This study will provide theoretical guidance and technical support for the recycling and utilization of SSR, which is beneficial for improving its economic value.