Study On Preparation And Emulsifying Properties Of Hydrolysates Made By Limit Enzymatic Hydrolysis Of Sweet Potato Heat-denatured Protein

The waste solution which produced starch in sweet potato processing contains large amounts of sweet potato protein. Sweet potato protein has significant bioactive functionality and it is a high-quality plant protein with good processing characteristics. Recycling sweet potato protein use heat-denatured and precipitation method from waste solutions can reduce the waste of resources and the pollution to the environment, so how to develop and utilize the sweet potato heat-denatured protein resources had become tough problem which urgently need to solve in starch industry in China.In this topic, sweet potato heat-denatured protein (SPHP) was prepared through isoelectric and heat precipitation, the hydrolysates made by limit enzymatic hydrolysis of SPHP which treated with five different types of enzymes (Alcalase, As1.398, Neutrase, Pepsin, Trypsin) was investigated as well as to research theirs emulsifying properties, at the same time discuss the effect of high-pressure treated them on theirs emulsifying properties.Firstly, SPHP was hydrolysised with Pepsin, dry the supernatant and precipitate of enzymatic hydrolyzates, determne emulsifying activity index (EAI) and emulsifying stability index (ESI). Pick out the supernatant and10min of hydrolysis time which have good efficiently in emulsification. So one-factor experiment use10min of supernatant of every hrydrolysates. Then SPHP was hydrolysised with5kinds of enzymes. The effect of concentration of substrate, enzyme to substrate concentration ratio, pH value and temperature on the EAI and ESI was studied by one-factor experiment to get the best enzymatic hydrolysis condition. The surface hydrophobicity and composition of amino acids of hydrolysates which made under this condition. Results showed the value of surface hydrophobicity were461.8,381.76,727.03,666.87and454.57, the content of THAA were157.24、211.24、203.6、268.21and239.11mg/100g Peptide.Secondly, the solubility of supernatant and precipitate each hydrolysates and average droplet size (d4,3), EAI, ESI, emulsion microstructure and apparent viscosity of supernatant and precipitate from emulsions of each hydrolysates were determined or observed respectively at emulsifier concentration was0.1%and oil volume fraction was25%condition. The results showed that the solubility of supernatants and precipitates were increased, but the solubility of precipitates were increased with less range than that of supernatants. D4，3of SPHP was71.96μm as a control, however d4,3of the hydrolysates including supernatants and precipitates were decreased, and supernatants had a lower d4,3values than that of precipitates. D4,3of supernatant of pepsin hydrolysates showed a smallest value was14.94μm. The emulsion droplets of supernatant hydrolysates became more homogenous in size, while the precipitate hydrolysates still retained big size and inhomogeneity. In addition, EAI of SPHP was11.21m2/g, but EAI of the hydrolysates including supernatants and precipitates were increased markedly (P<0.05),and the supernatant of pepsin hydrolysate had a highest EAI value (70.32m2/g). Furthermore, ESI value of the hydrolysates were increased. Compare with precipates, supernatants had a lower apparent viscosity and all emulsions were shear-thinning non-Newtonian fluids.Finally, the emulsions of every hydrolysates were treated by high-pressure, pick out the one which is the best efficiently in emulsification. The effects of high pressure homogenization conditions (different high pressure and time level) on EAIand ESI of SPHP-Al emulsions were evaluated. Under the optimum homogeneous conditions, effects of SPHP-Al concentration and oil volume fractions on EAI, ESI, d4,3and viscosity were investigated. The results showed that under high pressure homogenization at50MPa for1min, the effect of emulsification is the best, EAI and ESI of the SPHP-Al emulsion increased by4times and8times respectively, compared with those of untreated SPHP-Al emulsions. Under this condition, with the increase of SPHP-Al concentration, the EAI, droplet size and apparent viscosity of SPHP-Al emulsions were greatly decreased, while there was a pronounced increase in the ESI; On the contrary, with the increase of oil volume fraction, the EAI, droplet size and apparent viscosity of SPHP-A1emulsions were increased significantly, but the ESI had a marked decrease.The results proved that limit enzymatic hydrolysis treated with SPHP was a viable and effective approach which can improve its emulsifying properties. High pressure homogenization, emulsifier concentration and oil volume fraction can affect emulsifying properties significantly.