| Purple-fleshed sweet potato（PFSP） anthocyanins are natural pigment with attractive colors, they can be absorbed easily, and offer many health benefits. However, temperature, pH, light, oxygen, metal ions, enzymes and other factors may cause the degradation of PFSP anthocyanins, and the loss of their colors and health functions, which would limit the application of PFSP anthocyanins. So it is significant to research the degradative regulation and protective method of PFSP anthocyanins. At present, the research on the degradation of PFSP anthocyanins in the long-term storage was not comprehensive, and the methods about protecting PFSP anthocyanins were few and hardly effective. In this study, the identification and quantitation of the anthocyanins in 12 PFSP cultivars were carried out, the thermal degradative products of PFSP anthocyanins were detected and the degradative path was speculated, the degradative regulation of total anthocyanins, momomeric anthocyanins and colors in the process of high temperature heating and long-term storage were analyzed, the protective effect of β-cyclodextrin, whey protein and soy protein on the PFSP anthocyanins were studied.First, the identification of the anthocyanins in 12 Chinese PFSPs（’Jihei 1’, ’Xuzi 3’, ’Xuzi 6’, ’Zhezi 4’, ’Ningzi 1’, ’Ningzi 2’, ’Ningzi 3’, ’Ning 2-2’, ’Ning 6-8’, ’Guangzi 1’, ’Ziluolan’, and ’Qinzi 1’） was carried out by UPLC-PDA, QTOF-MS and MS/MS, the quantitation was conducted with cyanidin 3- glucoside as a standard. 13 anthocyanins were tentatively characterized, including 2 new PFSP anthocyanins, cyanidin 3-caffeoyl-vanilloyl sophoroside-5-glucoside and peonidin 3-caffeoyl-vanilloyl sophoroside-5-glucoside. The contents of the anthocyanins in the 12 PFSPs was 1018.7, 564.6, 112.3, 407.2, 150.0, 229.6, 103.9, 90.5, 253.2, 180.2, 381.9, 318.3 mg·100g-1 DW, respectively. ’Xuzi 6’ may be the only PFSP cultivar containing single anthocyanidin-based anthocyanins. In the other PFSP cultivars, the proportions of peonidin-based anthocyanins（59.374.8%） were far more than those of the cyanidin-based anthocyanins（25.240.7%）.2 anthocyanins were isolated and purified from PFSP pigment by pre-HPLC, they were peonidin 3-caffeoyl sophoroside- 5-glucoside and peonidin 3-caffeoyl-p-hydroxybenzoyl sophoroside-5-glucoside, respectively. The solutions were heated at 100°C by water bath for 0, 3, 6, 9 h, and their degradative products were detected by UPLC-PDA and QTOF-MS, and the degradative path was speculated to be that 3- and 5- glycosidic bonds were ruptured, the anthocyanins turned to be anthocyanidins, acylated sophoroses and glucoses; C-ring of anthocyanidins were opened to be two products, one was phloroglucinaldehyde, another would be differ with the groups on R1 and R2 position, that might be vanillic acid（from peonidin）, protocatechuic acid（from cyanidin） or p-hydroxybenzoic acid（from pelargonidin）; acylative group was ruptured from acylated sophorose to be phenolic acid and sophorose.Then PFSP pigment solutions were heated at 100°C by water bath for 10, 20, 30 minutes in the dark and light, respectively, and the solutions were stored at 25°C in the dark, 37°C in the dark, 25°C in the light for 6 months. The contents of the main 7 anthocyanins and 6 color parameters lightness L *, hue a*, hue b*, chroma c*, hue angle h and chromatic aberration ΔE of the solutions were detected. The results showed that the degradation of anthocyanins in the process of heating at 100°C in the dark and in the light was zero-order reaction kinetics. In the first 10 minutes, the degradation rates of anthocyanins in the light were higher than that in the dark, during 2030 minutes, the degradation rates in the light were relatively low. In the two ways of heating, the degradation percentages of peonidin 3-feruloyl sophoroside-5- glucoside（39.8% in the dark, 40.2% in the light） and peonidin 3-caffeoyl sophoroside-5- glucoside（39.8% in the dark, 40.0% in the light） were higher, which showed that their stability was worse; and the degradation percentages of peonidin 3-p-hydroxybenzoyl sophoroside-5-glucoside（22.6% in the dark, 18.6% in the light） were lower, which showed that its stability was better. There were no significant change trends in the 6 color parameters. The degradation of anthocyanins was also zero-order reaction kinetics in storage at 25°C in the dark, 37°C in the dark, 25°C in the light, the degradation percentages of peonidin 3-p-hydroxybenzoyl sophoroside-5-glucoside（56.9%, 89.0%, 18.6%） were highest, the degradation percentages of peonidin 3-caffeoyl-feruloyl sophoroside-5-glucoside（45.9%, 84.4%, 75.3%） were lowest, the degradation rates of monoacylated anthocyanins were higher than that of diacylated anthocyanins. The change in the 6 color parameters followed zero-order reaction kinetics. After comparing the degradation rates, half lives and degradation percentages of monomeric anthocyanins and total anthocyanins comprehensively, the influence of the three storage modes on the anthocyanins was 37°C in the dark > 25°C in the light>25°C in the dark.Pigment solutions at different concentrations of β-cyclodextrin, whey protein, soybean protein were prepared and heated by water bath at 100°C in the dark for 10, 20, 30 minutes, respectively. Then the solutions were stored at 25°C in the dark for 6 months. The contents of the main 7 anthocyanins and the colors of the solutions were detected, and the protective effect was compared. The results showed that in the process of heating at 100°C in the dark, the conservative percentage of total anthocyanins in the solution with 500 mg·L-1 of β-cyclodextrin decreased from 60.8% to 49.8%, it was adverse to the thermal stability of anthocyanins; in the solution with 2500 mg·L-1 of β-cyclodextrin, 50 mg·L-1 and 200 mg·L-1 of whey protein, 25 mg·L-1 and 50 mg·L-1 of soybean protein, and the conservation percentages of total anthocyanins increased to be 65.3%, 63.6%, 74.9%, 73.7% and 84.8%, respectively, they were favorable to the thermal stability of anthocyanins, but β-cyclodextrin, whey protein, soybean protein at two concentrations were adverse to the colors of PFSP pigment. In storage at 25°C in the dark, the degradation of monomeric anthocyanins and total anthocyanins, as well as the change in color of pigment solutions followed zero-order reaction kinetics. In the solutions with 500 mg·L-1 and 2500 mg·L-1 of β-cyclodextrin, 50 mg·L-1 of whey protein, 25 mg·L-1 and 50 mg·L-1 of soybean protein, the conservation percentages of total anthocyanins increased from 45.4% to 50.5%, 60.6%, 48.6%, 46.4% and 49.9%, respectively, they were favorable to the stability of anthocyanins, in the solution with 200 mg·L-1 of whey protein, the conservation percentage of total anthocyanins decreased from 45.4% to 41.6%, it was adverse to the stability of anthocyanins. After comparing, 500 mg·L-1, 2500 mg·L-1 of β-cyclodextrin were useful for the colors, 50 mg·L-1 of whey protein and 50 mg·L-1 of soybean protein did not show benefit to the colors of PFSP pigmen, 200 mg·L-1 of whey protein and 25 mg·L-1 of soybean protein was adverse to the colors of PFSP pigment. |
PDF Full Text Request