Soluble Protein From Heat-denatured Soybean Meal Fermented By Monascus Purpureus

Soybean meal obtained after soybean extracting oil has high protein, balanced amino acid composition and higher nutritional value. Therefore, the protein efficiently used from soybean meal becomes more important. Protein of heat-denatured soybean meal can be modified by microbial fermentation. Monascus is mainly used of manufacturing traditional food in China. It can secrete a variety of enzymes especially protease.Thus, heat-denatured soybean meal can be fermented by Monascus to produce soluble protein and to improve the utilization of protein assimilated easily to human. Product achieved is content of soluble protein, and has properties.In this study, solute protein(SP) and polypeptide(PP) from heat-denatured soybean meal fermented by Monascus purpureus 3.5833 were investigated. Results were as follows:(1) The molecular weight and content of SP and PP were researched from heat-denatured soybean meal fermentated by M. purpureus 3.5833(the original strain). The results showed that the macromolecule protein from heat-denatured soybean meal can be decomposed into PP with molecular weight 7.8~20.1k Da by M. purpureus 3.5833. The highest content of total SP reached(212.3±5.5) mg/g at 72 h, which was 2.56 times of SP from the original soybean meal. However, the highest content of total PP reached(105.7±1.8) mg/g at 96 h, which was 11.61 times of PP from the original soybean meal. Compared with SP, the highest content of PP needed some time of fermention, which lagged SP from heat-denatured soybean meal by M. purpureus 3.5833.(2) The strain of Monascus was screened from mutation strains by ultraviolet with preliminary screening and rescreening, in order to enhance utilization of protein from heat-denatured soybean meal. The strain of Monascus was irradiated using UV at 15 W and 30 cm for 50 s, its mortality rate was(82.7±2.2) %.Two consecutive mutagenesis using UV were carried out at preliminary screening stage. 100 larger treated colonies had been randomly inoculated into the preliminary screening medium at first mutagenesis for 144 h. Strains were selected for second mutagenic treatment according to larger ratio of diameter of hydrolysis circle to colony’s. And 9 strains were ultimately screened.The named strain 0409300 generating the highest content of total SP was screened in rescreening medium. The highest content of total SP was up to(263.7±3.2)mg/g from heat-denatured soybean meal fermented at 72 h by M. purpureus 0409300 and 3.18 times of the original soybean meal. The named strain 0501100 was screened generating the highest content of total PP from heat-denatured soybean meal fermented. The cultivated time of M. purpureus 0409300 was 24 h in seed medium, the hereditary of producing SP was stabler from heat-denatured soybean meal fermented by M. purpureus 0409300.(3) On the basis of the content of SP, the fementation parameters have been optimized in heat-denatured soybean meal fermented by M. purpureus 0409300, which included fermentation time, content of heat-denatured soybean meal, initial p H value, material volume, fermentation temperature and type and concentration of inorganic salt. Optimum conditions were 80 g medium of 11.25% soybean meal and 0.02mol/L Na2SO4 at original p H value in 500 m L. The content of total SP and PP were increased significantly and they were up to(290.9±3.4)mg/g and(106.6±0.9)mg/g respectively for 96 h at 28℃. And they were 3.52 and 12.25 times of the original soybean meal. Na2SO4 showed an increasing role on content of total SP and PP from soybean meal in a lower concentration.(4) FRAP, inhibition capacity on ABTS and O2- radical of products were researched from heat-denatured soybean meal fermented by Monascus as evaluation methods of antioxidant capacity. With the passage fermentation time, inhibition capacity on ABTS radical and FRAP of products from heat-denatured soybean meal fermented by M. purpureus 0409300 were higher than the original soybean meal, but inhibition capacity on O2- radical were reduced at later stage. FRAP and inhibition capacity on O2- radical of fermented product by M. purpureus 0409300 reached maximum at 24 h,(0.1889±0.0141)mmol/g and(6.74±0.30)U/g. Inhibition capacity on ABTS radical of fermented product at 120 h reached maximum(0.2176±0.0069)mmol/g. Under the same fermentation condition, products fermented by M. purpureus 0409300 and 0200107 were higher compared with others strains on FRAP and inhibition capacity on O2- radical. The products of them were of no significant difference.(5) Constituent and processing properties of product was determined from heat-denatured soybean meal fermented by M. purpureus 0409300. The contents of SP and PP in product were up to(900.6±10.8)mg/g and(305.6±2.7)mg/g respectively and content of polysaccharide reached(95.4±1.2)mg/g. The amount of amino acid was increased in product, especially, the concentration of Asp, Ser, Glu, Pro was larger increased than the original soybean meal. The solubilities of SP were better in the sample under neutral and alkaline at range of 87.6~95.7%, but solubility was the lowest under acid. Product has great emulsification and foaming capacity, but the emulsion stability and foam stability were poorer.