Wheat Gluten For Flavor Base And Purification And Identification Of Umami Peptide

Wheat gluten is a byproduct of the wheat starch industy,which is rich in Glu and Gln.It islow price and can be utilized as tasty substance. The technology that using koji fromsingle-strain and multi-strains ferment wheat gluten for tasty substance has the characteristicsof rich in flavor,low price and high efficiency. It has obviously shown more advantages thanthe commercial enzyme digestion in mass production.The koji-making conditions of Aspergillus oryzae cultivated with whole wheat wereoptimized and the effects of spores type,the raw material thickness degrees, culturehumidity,initial moisture content of the koji,culture time and culture temperature on neutraland acid protease activity were study.The results showed that the optimum koji-makingconditions were as follows:Guangming spores, raw material crushing to20mesh, initialmoisture content51%,culture time48h and culture temperature32℃under controlling culturehumidity.Under above conditions,the neutral protease activity of wheat koji was1583U/g,the acid protease activity was497U/g.Koji quality,physical and chemical properties of the fermentation process in koji-makingwith adding lacticbacteria during koji-making process were studied. The results showed thatthe addition of107cfu/g Lactic acid bacteria in koji-making could increase the neutralprotease which was increased by18.99%single-strain koji.The koji-making from Aspergillusoryzae and lactobacillus can significantly improve total nitrogen,amino acid nitrogen contentin the fermentation.The total nitrogen content is1.97g/100mL, amino acid nitrogen contentis1.07g/100mL, respectively increased by6.77%and12.83%than single Aspergillus oryzaekoji.By GC-MS analysis, koji which mixed by Lactic acid bacteria and Aspergillus oryzaeincreased the content of volatile aroma substances,such as3-methyl sulfonium propanal,3-methyl butyl aldehyde,benzene,formaldehyde,etc. Koji which mixed by Lactic acid bacteriaand Aspergillus oryzae significantly improved glutamic acid and free amino acid content offermentation broth, respectively increased by24.21%and18.98%than single Aspergillusoryzae koji.This Koji also enhanced the umami taste and overall coordination of thefermented broth.Wheat gluten with37%,55%and65%degrees of deamidation(DD) was fermented. Deamidated wheat gluten increased total acid,reducing sugar contents and reduced theproportion of hydrophobic amino acids at the end of fermentation. Wheat gluten with37%and50%DDs increased nitrogen content, wheat gluten with50%and65%DDs increasedfree amino acids content.Glu content increased with increasing DDs,Gln content reduced withincreasing DDs.Deamidated wheat gluten obviously increased umami sensory evaluation offermentation broth. The fermented broth of wheat gluten with50%DDs showed the strongestumami.One umami peptide was isolated and purified by ultrafiltration, gel filtrationchromatography and reverse high-performance liquid chromatography.The umami peptidewas identified to be Asp-Cys-Gly（DCG）by MALDI-TOF-MS and the molecular weightwas293.15Da.The taste characteristics of synthetical peptide was evaluated by taste dilutionanalysis,the results showed the umami taste threshold of synthetical peptide was100mg/Lwhich was one third of MSG taste threshold amount.200mg/L content of synthetical peptidehad umami-enhancing effect to the I+G, but it was no umami-enhancing effect of MSG.