title: Effect of endogenous ascorbic acid oxidase activity and stability on vitamin C in carrots (Daucus carota subsp. sativus) during thermal treatment.
abstract: 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 μM and 23.70 to 26.82 μmol/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 °C and inactivated above 50 °C. Irreversible thermal inactivation of AAO followed first order kinetics (55-70 °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 °C has resulted in total conversion of l-AA to DHAA due to residual AAO activity; a complete AAO inactivation was found in 80 °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 μg/g dry matter and the Nantes carrots had the highest vitamin C content. The effectiveness of rapid inactivation of endogenous AAO via heating (>80 °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.
authors: Department of Food Science, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand.
authors: Sze Ying
authors: SY
authors: Leong
authors: Indrawati
authors: I
authors: Oey
mesh_terms: D001205:Ascorbic Acid / Q000737:chemistry* / Q000378:metabolism; D018552:Daucus carota / Q000737:chemistry / Q000201:enzymology*; D004795:Enzyme Stability; D006358:Hot Temperature; D007700:Kinetics; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D010088:Oxidoreductases; D001205:Ascorbic Acid