Chisari Marco, Barbagallo Riccardo N, Spagna Giovanni
Dipartimento di OrtoFloroArboricoltura e Tecnologie Agroalimentari, DOFATA, Via Santa Sofia 98, 95100 Catania, Italy.
J Agric Food Chem. 2007 May 2;55(9):3469-76. doi: 10.1021/jf063402k. Epub 2007 Apr 4.
Polyphenol oxidase and peroxidase were extracted from two different varieties of strawberry fruit (Fragaria x ananassa D, cv. 'Elsanta' and Fragaria vesca L, cv. 'Madame Moutot') and characterized using reliable spectrophotometric methods. In all cases, the enzymes followed Michaelis-Menten kinetics, showing different values of peroxidase kinetics parameters between the two cultivars: Km = 50.68 +/- 2.42 mM ('Elsanta') and 18.18 +/- 8.79 mM ('Madame Moutot') mM and Vmax = 0.14 +/- 0.03 U/g ('Elsanta') and 0.05 +/- 0.01 U/g ('Madame Moutot'). The physiological pH of fruit at the red ripe stage negatively affected the expression of both oxidases, except polyphenol oxidase from 'Madame Moutot' that showed the highest residual activity (68% of the maximum). Peroxidase from both cultivars was much more thermolable as compared with PPO, losing over 60% of relative activity already after 60 min of incubation at 40 degrees C. The POD activation energy was much lower than the PPO activation energy (DeltaE = 97.5 and 57.8 kJ mol-1 for 'Elsanta' and 'Madame Moutot', respectively). Results obtained from d-glucose and d-fructose inhibition tests evidenced a decreasing course of PPO and POD activities from both cultivars as the sugar concentration in the assay medium increased. Changes in CIE L*, a*, b*, chroma, and hue angle values were taken as a browning index of the samples during storage at 4 degrees C. A decrease in L* was evident in both cultivars but more marked in 'Elsanta'. PPO and POD activities from cv. 'Elsanta' were very well-correlated with the parameter L* (r2=0.86 and 0.89, respectively) and hue angle (r2=0.85 and 0.93, respectively). According to these results, the browning of the fruit seemed to be in relation to both oxidase activities.
从两种不同品种的草莓果实（凤梨草莓‘Elsanta’和野草莓‘Madame Moutot’）中提取了多酚氧化酶和过氧化物酶，并使用可靠的分光光度法对其进行了表征。在所有情况下，这些酶均遵循米氏动力学，两个品种之间过氧化物酶动力学参数的值不同：Km = 50.68±2.42 mM（‘Elsanta’）和18.18±8.79 mM（‘Madame Moutot’），Vmax = 0.14±0.03 U/g（‘Elsanta’）和0.05±0.01 U/g（‘Madame Moutot’）。果实处于红熟期时的生理pH对两种氧化酶的表达均产生负面影响，但‘Madame Moutot’的多酚氧化酶显示出最高的残余活性（为最大值的68%）。与多酚氧化酶相比，两个品种的过氧化物酶对热更不稳定，在40℃孵育60分钟后，相对活性就已经损失超过60%。过氧化物酶的活化能远低于多酚氧化酶的活化能（‘Elsanta’和‘Madame Moutot’的ΔE分别为97.5和57.8 kJ mol-1）。从d-葡萄糖和d-果糖抑制试验获得的结果表明，随着测定介质中糖浓度的增加，两个品种的多酚氧化酶和过氧化物酶活性均呈下降趋势。在4℃储存期间，将CIE L*、a*、b*、色度和色相角值的变化作为样品的褐变指数。两个品种的L均明显下降，但在‘Elsanta’中更为显著。‘Elsanta’品种的多酚氧化酶和过氧化物酶活性与参数L（r2分别为0.86和0.89）和色相角（r2分别为0.85和0.93）具有很好的相关性。根据这些结果，果实的褐变似乎与两种氧化酶的活性都有关。
