The effects of storage temperature on the quality and phenolic metabolism of whole and minimally processed kale leaves

We studied the effects of storage temperature on the activities of phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO) in minimally processed kale (Brassica oleracea var. acephala) that was stored for 15 and 9 days at 5 ± 1ºC and 10 ± 1ºC, respectively. The main visual evidence for quality loss in whole leaves was yellowing and loss of turgescence. Minimally processed leaves presented significant browning, indicating increased POD and PPO activities. The PAL activity in minimally processed leaves stored at 5ºC was fourfold higher than that of whole leaves after two days of storage. We showed that minimal processing influenced PAL, POD and PPO activities. The activity of all enzymes studied increased during storage, indicating that changes in phenolic metabolism play an important role in the decline of kale quality. PAL activity increased rapidly at the beginning of storage and exhibited a reduced rate of increase over time, while the PPO and POD activities increased continuously over time. The storage at 5 ° C was a great ally in delaying changes in phenolic metabolism; however, the absolute PAL activity was higher at 5 than at 10ºC.本研究以最低程度加工的羽衣甘蓝（Brassica oleracea var. acephala）为材料，分别在5±1℃与10±1℃条件下储存15天和9天，探究了储存温度对其苯丙氨酸解氨酶（phenylalanine ammonia-lyase, PAL）、过氧化物酶（peroxidase, POD）以及多酚氧化酶（polyphenol oxidase, PPO）活性的影响。完整叶片的品质劣变主要视觉表征为黄化与膨压丧失；经最低程度加工的叶片则出现显著褐变，提示POD与PPO活性有所提升。储存2天后，5℃条件下储存的经最低程度加工叶片的PAL活性为完整叶片的4倍。本研究证实，最低程度加工会对PAL、POD及PPO的活性产生影响。所有被测酶的活性在储存过程中均呈上升趋势，表明酚类物质代谢的变化在羽衣甘蓝品质下降过程中发挥了重要作用：PAL活性在储存初期快速升高，随后增速随时间逐渐放缓；而PPO与POD活性则随储存时间持续上升。5℃储存可有效延缓酚类物质代谢的变化，但该条件下PAL的绝对活性仍高于10℃储存组。