酒精、pH及有機酸對於台灣藜 (Chenopodium formosanum Koidz) 甜菜色素色澤穩定性的影響

Abstract

The Contents of Abstract in This Thesis: Djulis (Chenopodium formosanum Koidz.) is a Taiwanese cereal plant containing betacyanins pigment. The betacyanins present in Djulis grains are betanin, isobetanin, amaranthin, and isoamaranthin, which are responsible for their color and antioxidant capacities. Betacyanins exhibit a beautiful red-violet color, but the color easily fades during processing or storage. It is quite sensitive to heat, pH, and alcohol which limit its application in food processing. An understanding of the degradation mechanism of Djulis betacyanin in alcohol, and how to improve the pigment quality during Djulis winemaking is needed. In this research, three parts of experiments were conducted. The first part was to elucidate the relative effect of ethanol and pH on pigment stability in aqueous extracts of Djulis. All samples were discussed based on thermal process and storage after pigment regeneration. The analyses of pigment stabilities (pigment retention, degradation index and betacyanins content), color qualities (Hunter L a b, chroma, Hue angle, and E) and kinetic studies of color degradation by activation energy (Ea), Gibbs energy of salvation (Gsal) were investigated. Then, the best condition was selected for further study of the effect of organic acids, including ascorbic, citric, and acetic acids, were used for the stabilization of the pigment. The antioxidant capacity (FRAP reducing power, DPPH scavenging ability, and TEAC) of Djulis extract with alcohol were investigated. Finally, the kinetic study was to investigate the effect of storage temperature on color loss (betacyanin degradation) of Djulis extracts in different concentrations of alcoholol. The rate constant (k) and activation energy (Ea) of pigment degradation of Djulis extract in various alcohol concentrations and organic acids addition during storage at different temperature (20-50C) were studied. Results showed that the pigment retention or red color of Djulis extract was more stable at pH 5.5 than that at pH 3.5. All samples showed that alcohol promoted the pigment degradation in Djulis extract. The hypsochromic shift (decrease of max) and isomerization of the pigment were more pronounced in the systems with higher ethanol concentrations. A stronger dependence of the discoloration on the ethanol concentration was observed, apparently due to the competing result between ethanol-water mixing and ethanol-betacyanin interaction. This effect was lowest in samples at 20%, v/v EtOH. Principal component analysis (PCA) indicated that color degradation of Djulis water extract was affected more by ethanol concentrations than by pH. For the color protection by organic acid, sample added with 1% ascorbic acid exhibited the highest pigment retention and color quality as compared to other treatments. This results explained by its best interaction with ethanol in the system. No matter before heated, after heated or stored in the sample added with 1% ascorbic acid could be found. The highest antioxidant capacities, such as FRAP reducing sugar, TEAC, and DPPH scavenging ability, were found in sample added with ascorbic acid of Djulis extract. The kinds of organic acid as well as the concentrations of alcohol were important factors in classifying the samples of Djulis water extract. Betacyanin degradation index (DI) was accelerated by ethanol and temperature. The rate of color loss during storage followed the first-order reaction kinetics. The higher ethanol concentration and temperature corresponded to the higher rate of color loss, which was in accordance with the trend of activation energy (Ea) of color degradation. For example, the Ea values of 0%, 10%, 20%, 40% and 60% EtOH samples were 81.04, 77.89, 71.75, 71.30 and 70.16 kJ mol-1, respectively. Therefore, the higher the alcohol concentration, the lower the activation energy of pigment degradation, and which lead to the less stability of the pigment. Keywords: Djulis, betacyanin stability, ethanol, organic acid, kinetic study, antioxidant capacity