Abstract: Sodium sulfate salting out was employed to selectively recover soybean trypsin inhibitor (STI) from soybean whey waste. The recovery conditions were optimized, and the physicochemical and interfacial properties of STI were evaluated. The results indicated that the yield of STI was 20.54% under optimal conditions: concentration of soybean whey to a solid content of 13%, adjustment to pH 4, and addition of 9 g/100 mL sodium sulfate. The main component of STI was Kunitz trypsin inhibitor (KTI, 20.1 kD) as indicated by SDS-PAGE analysis. The trypsin inhibitor activity towards Nα-benzoyl-DL-arginine 4-nitroanilide hydrochloride (BAPNA) of STI was 2 135.00 TIU/mg at pH 7. It was stable in a broad pH range from 2.0 to 11.0 and at a temperature up to 80 ℃. The inhibitory activity (73.19%) was still maintained at a high level after heating at 80 ℃ for 30 min. The FTIR and CD spectra showed that the structure of STI was highly similar to that of the commercial KTI (Sigma T9128). The dynamic surface tension and surface dilatational parameters of STI showed that the STI molecules could be quickly adsorbed to the interface to form a high elastic network and hence favorable foaming capacity and foaming stability. These findings suggest that the salting out method could be used as an effective strategy to prepare high-purity STI from soybean whey, and STI would emerge as a promising molecule for functional foods and medical applications because it exhibits excellent temperature and pH stability and high bioactivity.

Key words: soybean whey wastewater, salting out method, trypsin inhibitor, physicochemical properties, interfacial properties