Study On The Hydrolysis Of Soy Protein Isolate In An Enzymatic Membrane Reactor

Enzymatic production and use of functional and bioactive protein hydrolysates continues to gain prominence in the food industry. Conventional protein hydrolysis performed in the traditional batch reactor is a very popular process; however, it also has several disadvantages. Alternatively, use of ultrafiltration and/or nanofiltration membranes coupled to a hydrolysis tank to provide simultaneous separation of the hydrolysates from the reactants was found attractive. Hydrolysis of proteins (SPI) in enzymatic membrane reactors (EMR) is a promising technology. The hydrolysis of SPI was studied in an EMR in this article.Alcalase 2.4L(EC 3. 4. 21. 62)and Protease N(IUB 3. 4. 24.28) were used to hydrolysis SPI in the batch reactor or the enzymatic membrane reactor and the hydrolysis characteristic of two proteases was studied. Protease N had the higher proteinase activity on SPI, the lower optimum temperature and better stability and easier inhabited by hydrolysates. The hydrolysate molecular weight contents of two enzymes were lower than 10000 and the FAA contents were very low. Protease N was an suitable enzyme and was chosen for application in the EMR.To obtain the optimum condition of hydrolysis processing in the EMR, the initial water permeates Ji, initial protein concentration [S] and initial enzyme concentration [E]/[S] were varied and optimized using response surface methodology. The average permeate flux (Javerage), nitrogen recovered in permeate ( apparent sieving, Sapparent) and the hydrolysis degree of the permeate (DHpermeate) were determined. The quadratic model regression equation obtained revealed that all the three factors had significant but dissimilar influences on Javerage, Sapparent and DHpermeate. The optimum conditions were as follows: Ji =10mL/min,[S] = 4%(w/v),[E]/[S] = 1.5%(w/w). Under these conditions, the optimized values were 71.20% and 42.55% and 32.35% for Javerage , Sapparent, and DHpermeate respectively.In order to justify the use of EMR, the hydrolysates need to be characterized for their functional and bioactive properties. The hydrolysates was desalted by a kind of macroporous adsorption resin (MAR) and desorbed with different concentration ethyl alcohol in a breaker. The results showed: the hydrolysates had better solubility, lower viscosity and better antioxidative activity. The ash contents of the permeates fractions was significantly reduced following adsorption onto the MAR, the desalt ratios were 90.72%,92.89% and 93.29% respectively, the protein adsorption recoveries were 42.37%, 28.16% and 15.98% respectively after desorbed with different concentration ethyl alcohol. The antioxidative activity and ACE inhibitor activity of the product were better than the hydrolysates undesalted and increased with the increasing concentration of ethyl alcohol. The IC50 of the hydrolysates decreased from 0.418g/mL before desalted to 0.104mg/mL after desorbed using 95% ethyl alcohol.