Browning And Color Protection Of White Soy Sauce During Storage

White soy sauce, produced in northern of Jiangsu, is one kind of light color soy sauce with traditional characteristics. However, its color will change gradually from light golden to deep red brown during storage, affecting its color stability and consumer acceptability, decreasing its nutritional value and quality and restricting its application in food industry. In this paper, changes of physico-chemical properties of white soy sauce during storage were studied to find effective color protection methods maintaining its color stability.Effects of temperature, oxygen and illumination on the color of white soy sauce were investigated based on coloration index to explore the relation between storage conditions and its color stability. Results showed that the changes in coloration of white soy sauce at different temperatures fitted to a zero-order kinetic model lnk=23.73-5.42/RT, and the activation energy for browning reaction was 45.02 k J/mol. The higher the oxygen content in the package was, the darker was the white soy sauce. However, the removing of a small amount of dissolved oxygen inside white soy sauce played a certain role in promoting the color browning in initial stage of storage. But the promotion weakened with the storage time and inhibited the browning reaction ultimately. Illumination had a slight accelerative effect on browning.Relations between browning of white soy sauce and Maillard reaction, oxidative polymerization of phenols were studied by analyzing the physico-chemical properties indexes during storage. Maillard reaction was investigated based on amino acids and reducing sugar, two kinds of main reactants in Maillard browning. The content of total amino acids decreased by 0.52 g/100 m L in 30 days at storage temperature 40℃. To be specific, the content of alanine, glycine and methionine remained almost the same and that of tyrosine increased significantly, while the other free amino acids showed a downward tendency. The amount of glutamic acid decreased by 0.39 g/100 m L, accounting for 75% of total amino acids loss. The content of total reducing sugar decreased by 2.99 g/100 m L, among which the glucose accounted for 2.05 g/100 m L while the content of other reducing sugars, including arabinose, xylose, galactose and fructose occupied the rest 0.44 g/100 m L. It was concluded that browning would be mostly ascribable to the formation of melanoidins between glucose and glutamic acid, which were the dominant reducing sugar and amino acid in white soy sauce. Oxidative polymerization of phenols was investigated based on total phenols index. Total phenols only decreased by 0.21 mg/m L, which meant phenols of white soy sauce during storage were relatively stable and was not prone to oxidative polymerization causing deeper color.In the experiment of the color protection of white soy sauce, effects of several browning inhibitors on the white soy sauce during storage were studied. Results showed that the activity sequence of browning inhibitors at initial stage of storage was L-cysteine>phytic acid>calcium chloride>critic acid>ascorbic acid>sodium sulfite, and in the late of storage the sequence was calcium chloride> phytic acid>critic acid>sodium sulfite>ascorbic acid>L-cysteine. The inhibition rate of L-cysteine and ascorbic acid decreased remarkably and that of calcium, phytic acid and sodium sulfite declined not obviously. The browning inhibiting activity of calcium chloride, phytic acid and critic acid improved with the increase of addition within the allowing range. Using Box-Behnken response surface analysis, it was concluded that a highly significant(P<0.01) positive correlation between calcium chloride, phytic acid and critic acid and the color of white soy sauce, and there exited marked interaction between phytic acid and critic acid. The activity order of the three inhibitors on white soy sauce was phytic acid>critic acid>calcium chloride. The optimized composite of browning inhibitors for white soy sauce was calcium chloride 0.08%, phytic acid 0.01%, critic acid 0.09%, and the inhibition ratio in theory was 36.32%. The composite was proved to be effective by experimental studies, in which the inhibition ratio was 35.56%.Quality of white soy sauce brewed with starch and gluten was studied in the experiment of making complex formulation with alternative materials. Results suggested that the coloration of soy sauce brewed with different raw materials was as follows: corn starch>mixed starch>wheat starch>flour, which meant the separation of wheat starch and gluten in flour could not inhibit the browning of white soy sauce. Comparing with the control sample from wheat flour material, soy sauce brewed with wheat starch had higher content of amino acids and lower reducing sugar. While both the amino acids and reducing sugar contents of soy sauce brewed with corn starch were lower. In the flavor analysis, the order of flavors content of soy sauce brewed with different raw materials was flour>mixed starch>corn starch>wheat starch. Contents of phenols and esters of soy sauce from compound materials were lower remarkably than that from wheat flour.