Optimization of Protein Extraction and Analysis of Hypoglycemic Activity in Vitro of 6 Different Enzymatic Hydrolysates from Protein Mulberry Leaves

The protein extraction process of protein mulberry leaves and hypoglycemic activity in vitro of the enzymatic hydrolysates were studied aiming at further developing and utilizing protein resources in mulberry leaves. Protein mulberry leaf protein (PMLP) was extracted from protein mulberry leaves through the ultrasound-aided alkaline extraction and acid precipitation. The single factor experiments and response surface methodology were applied to optimize the extraction process of PMLP. The inhibitory rate of α-glucosidase was used as the evaluation index to analyze the hypoglycemic activity in vitro of different PMLP enzymatic hydrolysates. The results showed that the optimum extraction conditions of PMLP were as follows: NaOH concentration was 0.125 mol/L, extraction temperature was 40 ℃, extraction time was 40 min and liquid-solid ratio was 37:1 mL/g. Under these conditions, the actual extraction rate of PMLP reached 49.59%±0.45%, the obtained protein isoelectric point was pH3.5, the water holding capacity was 6.49±0.49 g/g, the oil holding capacity was 2.59±0.06 g/g, the emulsifying activity was 7.40±0.17 m²/g, and the emulsion stability was 72.48%±3.03%. The hypoglycemic activity in vitro of the PMLP enzymatic hydrolysates digested by compound protease hydrolysate, flavor protease hydrolysate, alkaline protease hydrolysate, trypsin hydrolysate, neutral protease hydrolysate and papain was investigated. Among the enzyme species examined, the neutral protease hydrolysate of PMLP demonstrated the highest inhibitory effect on α-glucosidase with IC₅₀=3.52 mg/mL. According to results of the study, the extraction process of PMLP was stable, and the PMLP enzymatic hydrolysate digested by neutral protease had strong hypoglycemic activity in vitro, which would provide a reference for the further development of protein mulberry leaf protein and peptides resources.