Study On The Preparation And Browning Resistance Of New White Fermented Bean Curd

Fermented bean curd is a traditional fermented soybean product in our country. It is welcomed by more and more domestic and foreign consumers because of its delicious taste, low price and great health care function. For the traditional white fermented bean curd, Maillard browning which occurs in its late fermentation and storage time deepens its color, affectting its appearance and limiting the expansion of consumer market. This study was made to develop New white fermented bean curd by changing the composition of after fermentation soup in order to inhibit the Maillard browning preliminarily. Then New low-browning white fermented bean was developed by addition of cysteine on the basis of New white fermented bean curd. The sensory quality was improved and the flavor was enhanced. The study investigated the changes of browning degree, chemical composition, texture, color difference and flavor in the late fermentation process of New white fermented bean curd, monitoring the formation law of small molecular intermediates and melanoid of Maillard reaction during the late fermentation period, exploring the best additive time of cysteine as Anti-browning Agent and observing the stability of Anti-browning ability during the 10 months’ storage time of three kinds of fermented bean curd.The effect of the content of GOD enzyme and the substitution ratio of glutinous rice wine on the quality of New white fermented bean curd was evaluated. The results indicated that the browning degree was decreased significantly, total acid and amino acid nitrogen content were increased, texture characteristics were improved by addition of enzyme. When the substitution ratio reached 40%, the sensory and texture quality of New white fermented bean curd were significantly reduced. The optimal combined process was confirmed under the following conditions: substitution ratio 30%, GOD enzyme 0.02%(w/v). The Anti-browning effect and the changes of physical and chemical properties of New white fermented bean curd in two different additive ways of Anti-browning Agents were investigated, the results showed that the darkening of New white fermented bean curd was further suppressed, total acid and amino acid nitrogen content were significantly increased, the late fermentation time could be shortened greatly. 0.20%(w/v) cysteine was finally selected as the optimum additive amount combined with sensory evaluation results, the New white fermented bean curd prepared under this condition was called New white and low-browning flavored fermented bean curd.Comparing the content of free amino acid and volatile flavor compounds in three kinds of fermented bean curd(blank fermented bean curd, New white fermented bean curd, New low-browning white fermented bean curd) after late fermentation period, the results showed that the contents of free amino acids in New white sample and New low-browning sample were increased 13.27% and 4.58% respectively compared with the blank one. Among them, New low-browning white fermented bean curd had the best amino acid composition as the umami and sweet taste amino acid ratio were increased while the bitter amino acid ratio were reduced. By SPME-GC-MS test, it could be found that the content of volatile flavor compounds of New low-browning white fermented bean curd were increased 36.17%, for the other two fermented bean curds, the contents of volatile flavor compounds were almost similar. New low-browning white fermented bean curd generated more abundant alcohols and aldehydes eapecially higher content of n-hexenal and enals such as octanal, nonanal and trans-2-octene aldehyde.(E,E)-2,4-nonadienal detected could provide the chicken flavor. Cysteine added during the late fermented period endowed fermented bean curd with rich fat incense and solved the problem of not good flavor.Ultraviolet-Visible Spectrum characteristics of fermented bean curd system were studied, A294 and A420 values were used as characterizations of small molecular intermediates and melanoid respectively to explore the variation of Maillard reaction products(MRPs). The results showed that: The absorbance value of blank system increased fastest during the whole late fermentation period, The New white fermented bean curd system maintained a stable growth rate, The formation rates of small molecular intermediates and melanoid in New low-browning fermented bean curd system increased first and then decreased, indicating that cysteine took role in Maillard reaction and acted on AMD products to block the production of melanoid at the same time.