Study On The Controlled Preparation Of Fermented Bean Curd Flavor Condiments And Their Application

Fermented bean curd is a traditional fermented soybean product in China. It has unique flavor and rich nutrition. Many consumers like fermented bean curd. However, the fermented bean curd flavor condiment on sale exerts poor mouthful. On the other hand, plant food source has become a popular direction of flavoring industry. During the fermentation of bean curd processing, a lot of bean curds are wasted, which can be used as a source of high quality vegetable protein. Therefore, fermented bean curd and bean curd were used as raw materials to prepare the flavor condiments using biological enzymatic hydrolysis and Maillard reaction technology, which was nutritious, natural, safe, and full-bodied. The main contents are listed as follows:The optimum conditions of multiple enzymatic hydrolysis were obtained as follows: a substrate concentration 6%(w/v), endoprotease A concentration of 2500 U/g, hydrolysis time 2 h at 55 oC, followed by addition of 2000 U/g of exoprotease D for further 2 h at 50 oC. The degree of hydrolysis was 15.72% under optimum conditions and the obtained bean curd peptides Maillard reaction products(MBP)exerted very good flavor enhancing properties.The color-inhibiting mechanism of bean curd peptide-xylose system was further investigated. These mixtures were first reacted at 120 oC for 10 min, then added cysteine and maintained temperature at 120 oC for 110 min. The color of Maillard reaction products was lighter(MBP-10). The two stages gradient temperature-elevating Maillard reaction was used to prepare light-colored MRPs. The lightest-colored MRPs(MBP-90) was obtained as follows: the reaction mixtures were kept at 80 oC for 90 min, then cysteine was added and the temperature was increased and maintained to 120 oC for 110 min.MBP, MBP-10 and MBP-90 were compared in terms of sensory evaluation, the content of total and free amino acids, relative molecular weight distribution and volatile compounds were evaluated. MBP-90 exerted the best meaty, salty taste, mouthfulness, better continuity and overall acceptability, MBP exerted the best caramel and bitter. The content of bitter peptide-bound amino acids: MBP>MBP-10>MBP-90, the content of sweet free amino acids: MBP-90>MBP>MBP-10, the content of umami free amino acids: MBP-90>MBP>MBP-10. The relative molecular weight content below 180 of MBP, MBP-10, MBP-90 were 179.62%, 175.10%, 176.92% higher than that of BP, respectively, while peptides between 500~1000 in MBP, MBP-10, MBP-90 were 33.33%, 32.96%, 33.04% lower than that of BP, respectively. The alcohols compounds, furan(no sulfur-containing) compounds and nitrogen compounds content were high in MBP. The sulfur-containing compounds content were high in MBP-90. Flavors compounds were indentified by GC-O. 1-octen-3-ol, 2-pentyl furan, glycosyl mercaptan and 2-butylpyridine were key volatile flavor compounds. They could be found in MBP, MBP-10 and MBP-90.Based on DH and sensory evaluation, the optimum conditions of enzymatic hydrolysis were obtained as follows: substrate concentration 6%(w/v), Papain concentration 2500 U/g, hydrolyzing for 3 h at 55 oC. The degree of hydrolysis was 7.4% under these optimum conditions and the MRPs exerted very good flavor.The umami free amino acids content and sweet free amino acids content in MFP increased 101.46% and 13.05% compared with original fermented bean curd peptides(FP), while the bitter peptide-bound amino acids content decreased 74.73%. The relative molecular weight content below 180 in MFP was 28.85% higher than that of FP, while peptides between 500~1000 in MFP were 41.27% lower than that in FP. The alcohol compounds, ester compounds and heterocyclic compounds content were higher in MFP than in fermented bean curd powder. Flavors compounds were indentified by GC-O. There were oleic acid ethyl ester, linoleic acid ethyl ester, ethano and 2,3-butanediol in MFP and fermented bean curd powder, these volatile flavor compounds exhibited ester aroma. MFP contained a lot of heterocyclic compounds, they exhibited strong meaty, caramel and roasted aroma.The MBP-90 was added to chicken soup and sushi ginger, while the MFP was added to bean paste and sweet bean paste. Results of the applications indicated that the flavor condiments kept the original flavor and color of food products and enhanced their flavor properties.