| Wheat gluten is a by-product of wheat starch processing with a high nutritional value at relatively low cost.The insolubility of gluten in aqueous solutions is one of the major limitations for its more extensive use in food and fermentation industries.Therefore,enzymatic hydrolysis of wheat gluten to produce various food or feed grade products has been developed to enlarge the field of its applications.However,the limits of equipments and process control results in the high content of insoluble fraction and poor dispersion of wheat gluten hydrolysate.Hence,the present study aimed to find the main factors affecting the solubility and appearance quality of wheat protein hydrolyzate produced by the cooperated company by analyzing its physicochemical properties,investigate the effect of treatments of high temperature heating,high temperature and pressure treatment,and protease-amylase hydrolysis on the physicochemical properties and microstructure of produced wheat peptone,evaluate its potence to be used as nitrogen source for cell growth of vaccine and lactic acid bacteria,and production of natamycin,and finally conclude the possible mechanism of wheat peptone promoting the growth of Lactococcus lactis cells.The main conclusions were as follows:(1)Wheat protein hydrolyzate(WPH)produced by the cooperated company has the soluble fraction of about 70.20%(w/w)and insoluble fraction of 29.80%(w/w)with poor dispersion.In the insoluble fraction,protein and starch contents occupied about 77.21%(w/w)and 21.43%(w/w),respectively.The treatments of WPH with high temperature heating and high temperature and pressure treatment decreased the soluble fraction contents to 67.98% and 65.49%,respectively.Based on the degree of hydrolysis and soluble fraction content,the protease-amylase hydrolysis process parameters were optimized as: substrate concentration 30 g/L,temperature 55 °C,pH 5.5,combination of 2.5-h hydrolysis with flavourzyme(2500 U/g)followed with 0.5-h with ?-amylase(50 U/g)and glucoamylase(100 U/g).Under this condition,the hydrolysis degree of WPH was 6.52% and soluble fraction content achieved to 92.87%.(2)According to the wheat peptone yield,moisture content and PDI,the spray drying parameters of wheat peptone were optimized as follows: inlet air temperature 200 °C,compressed air flow 600 L/h,the feed rates 7.0 m L/min and feed concentration 80 g/L.The obtained wheat peptones from protease-amylase hydrolysis(WP-1),high temperature heating(WP-2)and high temperature and pressure treatment(WP-3)showed higher protein content(>80%)and solubility(PDI >99%)than those of WPH.The ratios of peptides with molecular weight(Mw)above 5000 u in WP-1,WP-2 and WP-3 decreased to 0.21%,2.34% and 0.89%,respectively,and those with Mw below 180 u increased to 30.08%,6.28% and 7.55%,respectively.(3)The microstructures of wheat peptones were observed and anaylzed using optical microscope,SEM,FTIR and AFM.Results showed that the particle sizes of wheat peptones WP-1,WP-2 and WP-3 significantly decreased with smooth surfaces of large particles and wrinkled surface of small ones.WP-2 and WP-3 samples showed agglomerating modes.AFM analysis showed that WP-1 had the low surface roughness with Rq and Ra of 0.361 nm and 0.165 nm,while WP-3 had a polymerized form with a width of 2.1 ?m.FTIR data showed that the typical peaks of WP-1,WP-2 and WP-3 had the same trends with WPH.Compared with other commercial peptones,the prepared wheat peptone WP-1 met the requirements of peptone quality standards with high protein content(82.45%),solubility(PDI >99%)with comprehensive amino acids and molecular weight distribution of peptides.(4)The prepared wheat peptone WP-1 benifited the cell growth of lactic acid bacteria(L.casei,L.lactis,L.reuteri and L.plantarum)and vaccine(Brucella suise S2),and significantly impoved natamycin production.Further results proved that L.lactis cells mainly absorbed the peptides with Mw of 180~2000 u and the amino acids inlucding serine,glutamic acid,methionine,isoleucine and lysine for growth. |
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