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

Abstract

ABSTRACT. We studied the effects of storage temperature on the activities of phenylalanine ammonialyase (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.Keywords: Brassica oleracea cv. acephala, enzymatic browning, peroxidase, polyphenol oxidase, phenylalanine ammonia-lyase.Efeito da temperatura de conservação na qualidade e no metabolismo fenólico de folhas de couve inteiras e minimamente processadas RESUMO. Estudou-se o efeito da temperatura de armazenamento e do processamento mínimo sobre a atividade da fenilalanina amônia-liase (PAL), peroxidase (POD) e polifenol oxidase (PPO), em folhas de couve (Brassica oleracea var. acephala) por 15 e 9 dias, nas condições de 5 ± 1ºC e de 10 ± 1ºC, respectivamente. O amarelecimento e a perda de turgescência foram as principais causas para a redução da qualidade visual das folhas inteiras, enquanto nas folhas minimamente processadas apresentaram também, escurecimento, que coincidiu com o aumento na atividade da POD e PPO nas duas temperaturas estudadas. A atividade da PAL em folhas minimamente processadas mantidas a 5ºC mais que dobrou até o segundo dia de conservação em relação às conservadas a 10ºC. O processamento mínimo influenciou a atividade da PAL, POD e PPO. Todas as enzimas avaliadas, aumentaram a atividade durante a conservação, seja no início, no caso da PAL, ou no final, para a PPO e POD, indicando que as mudanças no metabolismo fenólico desempenha um papel importante no declínio da qualidade de couve. A conservação a 5ºC retardou as alterações no metabolismo fenólico, embora nessa temperatura, a atividade da PAL foi maior, em grandeza numérica, em relação às folhas armazenadas à 10ºC.Palavras-chave: Brassica oleraceae cv. acephala, escurecimento enzimático, peroxidase, polifenol oxidase, fenilalanina amônialiase.

Association of preharvest management with oxidative protection and enzymatic browning in minimally processed cassava

“…The assay for POD was conducted in accordance with Simões, Moreira, Mosquim, Soares, and Puschmann (), with 100 μl of supernatant added to a reaction medium containing 1 ml of potassium phosphate buffer (0.2 M, pH 6.0), 100 μl of guaiacol (40 mM) and 100 μl of hydrogen peroxide (23 mM), previously maintained at 25ºC in a dry bath. Absorbances were obtained using a spectrophotometer at 470 nm, at a temperature of 25ºC, for 3 min, with a 30‐s interval between readings.…”

Darkening, damage and oxidative protection are stimulated in tissues closer to the yam cut, attenuated or not by the environment

“…In lettuce, it seems that the increase in PPO activity is not due to injury, unlike POD activity . Conversely, in cabbage leaves, PPO activity increases soon after injury, while POD activity remains unchanged . It is also reported that physical trauma may induce de novo synthesis of PPO in lettuce …”

“…PPO and POD activities were determined as detailed adapted by Simões et al . A 0.25 g sample of external (0–5 mm) or internal (5–10 mm) tissue was homogenized in 6 mL of 0.2 mol L −1 sodium phosphate buffer (pH 6.0) precooled to 4 °C.…”

QUALITY OF MINIMALLY PROCESSED YAM (Dioscorea sp.) STORED AT TWO DIFFERENT TEMPERATURES

“…c) Extraction and determination of polyphenoloxidase activity (PPO, EC 1.14.18.1) were carried out as described by Silva (1981) and adapted by Simões et al (2015). A sample of 0.25 g with a height of 1,000 mm, 1000 mm width, and 5 mm thickness from the surface tissue located on the equatorial side of the yam slice.…”