Tudela Juan Antonio, Hernández José Antonio, Gil María Isabel, Espín Juan Carlos
Research Group on Quality, Safety, and Bioactivity of Plant Foods, Department of Food Science and Technology, CEBAS-CSIC. P.O. Box 164.30100 Espinardo, Murcia, Spain.
J Agric Food Chem. 2003 Jul 16;51(15):4296-302. doi: 10.1021/jf030071s.
L-galactono-gamma-lactone dehydrogenase (GLDH) activity and vitamin C content as ascorbic acid (AA) plus dehydroascorbic acid (DHA) were evaluated in five potato tuber cultivars (Agata, Altesse, Franceline, Manon, and Monalisa). The effect of fresh-cutting and subsequent refrigerated storage of Manon potato under different atmospheres (air, 20% CO(2) + air, 100% N(2), and vacuum packaging) on GLDH activity and vitamin C content was also determined. GLDH from the five potato tuber cultivars showed typical inhibition kinetics by high substrate concentration in the synthesis of AA from its physiological precursor L-galactonic acid-gamma-lactone (GL). GLDH activity was not correlated with the corresponding vitamin C content in any potato tuber cultivar. GLDH from all the cultivars presented a major isoform with isoelectric point (IEP) 5, which changed to IEP = 4.3 after minimal processing. In addition, the GLDH-catalyzed synthesis of AA by the new isoform showed typical Michaelis kinetics, in which the enzyme became more efficient to catalyze the reaction. Whether the change in the isoform pattern was due to either post-translational modifications or de novo synthesis of a new isoenzyme remains unanswered. Fresh-cutting increased GLDH activity from 4.7-fold (vacuum packaging) to 11-fold (air) after 6 days. In addition, 100% of vitamin C content was retained in air and decreased in the rest of atmospheres after this storage period, following the sequence vacuum packaging (89%) > 100% N(2) (78%) > 20% CO(2) + air (63%). This tendency was correlated with the corresponding GLDH activity detected in each storage atmosphere, except in the case of 20% CO(2) + air. Vacuum packaging proved to be the best storage condition, because fresh-cut potatoes did not turn brown and retained 89% of initial vitamin C content.
在五个马铃薯品种（阿加塔、阿尔泰斯、弗朗塞琳、玛侬和蒙娜丽莎）中评估了L-半乳糖酸-γ-内酯脱氢酶（GLDH）活性以及以抗坏血酸（AA）加脱氢抗坏血酸（DHA）形式存在的维生素C含量。还测定了玛侬马铃薯在不同气氛（空气、20% CO₂ + 空气、100% N₂和真空包装）下鲜切及随后冷藏储存对GLDH活性和维生素C含量的影响。五个马铃薯品种的GLDH在从其生理前体L-半乳糖酸-γ-内酯（GL）合成AA的过程中表现出典型的高底物浓度抑制动力学。在任何马铃薯品种中，GLDH活性与相应的维生素C含量均无相关性。所有品种的GLDH均呈现出一种主要的同工型，其等电点（IEP）为5，经过最少加工后变为IEP = 4.3。此外，新同工型催化的GLDH合成AA表现出典型的米氏动力学，其中该酶催化反应的效率更高。同工型模式的变化是由于翻译后修饰还是新同工酶的从头合成仍未得到解答。鲜切后6天，GLDH活性增加，从真空包装下的4.7倍增加到空气中的11倍。此外，在此储存期后，空气中维生素C含量保持100%，其余气氛中则降低，顺序为真空包装（89%）> 100% N₂（78%）> 20% CO₂ + 空气（63%）。这种趋势与在每种储存气氛中检测到的相应GLDH活性相关，但20% CO₂ + 空气的情况除外。事实证明，真空包装是最佳的储存条件，因为鲜切马铃薯不会变褐，且保留了89%的初始维生素C含量。
