| The nonenzymic browning reaction includes Maillard reaction, caramelizationand ascorbic acid browning among which Maillard reaction is the most commonbrowning reaction during storage or processing of food. It refers to complexinteractions between a reducing sugar (aldehydes or ketone) and amino compoundwhich has significant influence in nutritional value, color and flavor of food.Therefore, it is especially important for the food science to study Maillard reaction,which will be helpful to control it and let it react towards the good direction. Andkinetic study has always been a basic method to investigate the mechanism ofMaillard reaction and achiev the above goal. After reducing sugar, ascorbic acid hasbeen another compound with potential dicarbonyl group which attracts much attentionin Maillard reaction. The purpose of this study was to determine quantificationally ofthe residual concentration of reactants, brown index and the concentration ofimportant volatiles, and separately described their kinetics features varying with timeand temputure in ascorbic acid/cysteine model systems. The major content and resultsare as follows:1. UV spectrophotometry and HPLC methods were compared to determine theconcentration of ascorbic acid in Maillard system. The results showed that the linearlydependent coefficient was both above0.999and the results of two methodsdetermining3parallel samples were close. Since UV spectrophotometry was muchmore simple and rapid, it was more suitable for the determination of ascorbic acid inMaillard system. This paper also explored a method for quantitative determination ofcysteine and established the pre-column derivatization method using FDNB asderivating agent. In comparison with the SPEM, the technology of extracting flavorcompounds by using solvent was adopted. GC-MS, LRI and standard substance wereall used for qualitative determination and GC for quantitative determination ofvolatiles.2. UV spectrophotometry and pre-column derivatization methods were usedrespectively to determinate the concentration of ascorbic acid and cysteine. Theresults showed that cysteine would begin self-pyrolysis reaction at first, and thenascorbic acid reacted with its decomposition products. The fact that the concentrationof ascorbic acid at relatively lower temperature almost remained unchanged indicated that Maillard reaction nearly didn’t happen. The consumption rate of cysteinefollowed first order reaction kinetics while the kinetics of Maillard reaction wassecond order, the Ea was120.12kJ/mol and136.3kJ/mol respectively.3. Using the UV spectrophotometer to measure the absorbance at420nm and292nm, the kinetics feature of the brown index and its precursor were studied. Ingeneral, the rate or extent of browning increased with increasing time and temperatureduring the reaction, and the growth was more obvious at higher temperature.Comparing the change of the absorbance at420nm with the concentration of cysteine,we could find that the decomposition of amino acid did not produce pigment. Whilecomparing the absorbance with the concentration of ascorbic acid, we might find aquantitative relationship that the certain quantity consumption of ascorbic acid wouldlead to the same brown index. Comparing the absorbance at420nm and292nm, wecould see that the increase of brown index was slow at first, and then it grew as firstorder kinetics while the precursor had a relatively stable stage during the increasingprocess at all temperatures.4. By using the solvent extraction and the tridecane as internal standardsubstance, the kinetics feature of thiophene, thiophenone, thiazole and pyrazine werestudied through GC-MS and GC. The results showed that at low temperatures, noother products were found. However, the concentration and kinds of productsincreased as the temperature rose, but stopped increasing when the temperaturereached155℃.The dynamics feature of the flavor compounds had been analyzed. Because ofthe similar structure of2-acetylthiophene and3-acetylthiophene, their contents anddynamic changes were resembled as well. At high temperature, the concentration of2-propyltetrahydrothiophene increased at first and then decrease. Although thestructure of2-Methyltetrahydrothiophen-3-one and Tetrahydrothiophen-3-one weresimilar, their concentrations were in big difference. The contents and dynamicchanges of2-methyl-4-propylthiazole and2-Acetylthiazole were also different, whichindicated the difference of their generation mechanism. The methylpyrazine formationrate was constant according to the experimental data.This study helps better understanding the formation mechanism of aromacompounds from Maillard Reaction based on the ascorbic acid. It has a greatsignificance for providing theoretical basis to control reaction process. |
PDF Full Text Request