Effect of endogenous ascorbic acid oxidase activity and stability on vitamin C in carrots (Daucus carota subsp. sativus) during thermal treatment

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• 作者：Sze Ying Leong ; Indrawati Oey ; ^{indrawati.oey@otago.ac.nz}
• 关键词：Carrots ; Vitamin C ; Ascorbic acid oxidase ; Thermal processing ; Cultivars
• 刊名：Food Chemistry
• 出版年：2012
• 期刊代码：48_03088146
• 类别：abs
• 出版时间：15 October, 2012
• 卷：134
• 期：4
• 页码：2075-2085
• 文件大小：893 K

摘要

The purpose of this research was to study the effect of endogenous ascorbic acid oxidase (AAO) on vitamin C in carrots (Daucus carota subsp. sativus), namely Nantes, Egmont Gold and baby carrots during thermal treatment. Enzyme-substrate reaction kinetics of AAO were described using Michaelis-Menten equation. The estimated K_m and V_max values of AAO ranged from 50.34 to 63.54 渭M and 23.70 to 26.82 渭mol/min, respectively. Nantes carrots had the lowest AAO activity. On the other hand, Egmont Gold had the highest V_max. AAO activity in all carrot cultivars was stable up to 50 掳C and inactivated above 50 掳C. Irreversible thermal inactivation of AAO followed first order kinetics (55-70 掳C) and the estimated activation energy of the three carrot cultivars situated between 114.33 and 191.45 kJ/mol. Regarding vitamin C stability, thermal treatment at 60-70 掳C has resulted in total conversion of l-AA to DHAA due to residual AAO activity; a complete AAO inactivation was found in 80 掳C-treated carrots with high vitamin C retention predominantly in l-AA form, up to 90%. On average, the carrots had a total vitamin C content amounting from 368.24 to 379.87 渭g/g dry matter and the Nantes carrots had the highest vitamin C content. The effectiveness of rapid inactivation of endogenous AAO via heating (>80 掳C, 10 min) prior to matrix disruption gave protection to l-AA towards enzymatic oxidation, thus resulted in a higher vitamin C content and stability in carrots.