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

Enzyme assays are based on methodologies described in the literature. However, the enzyme kinetics must be adjusted to obtain more reliable results. This study aimed to adjust assays by testing different polyphenol oxidase (PPO) and peroxidase (POD) extract amounts and reaction times in sweet potato cultivars harvested at different times. Sweet potato cultivars Paraná, Mãe de Família, and ESAM1 were harvested at 120, 150, and 180 days after planting and minimally processed. A 0.25 g sample was used to determine PPO and POD activities immediately after minimal processing at each harvest. Extraction was performed in 1500 μL phosphate buffer (0.2 M, pH 6.0). The PPO assay was performed by adding 10-50 μL extract, 1490-1450 μL phosphate buffer (0.2 M, pH 6.0), and 1500 μL catechol (0.2 M). The POD assay was carried out by adding 10-50 μL extract to a reaction medium containing 1790-1750 μL phosphate buffer (0.2 M, pH 6), 100 μl guaiacol (5 g L-1), and 100 μL hydrogen peroxide (0.8 g L-1). In both cases, the evaluated reaction times were 1, 2, and 3 min. In the three cultivars, PPO and POD activities increased with the volume of extract and reaction time at all harvest times. The enzyme extract volume of 10 μL for 2 min promoted a continuous increase in PPO and POD enzyme activities in all studied cultivars and at all reaction times.

Baby carrot is a very perishable product mainly due to the abrasion of the cylindrical carrot root segments. The influence of four different controlled atmospheres (CA) (air, 2 kPa O 2 + 15 kPa CO 2 , 5 kPa O 2 + 5 kPa CO 2 and 10 kPa O 2 + 10 kPa CO 2 ) was studied to maintain quality and prolong the shelf life of baby carrots. Respiration rate (RR), the content of vitamin C, carotenoids and phenolics by HPLC as well as the sensory quality of baby carrots during storage at 4 °C were evaluated. The lowest RR was observed in baby carrots stored under CA containing the lowest O 2 concentrations. Baby carrots under low O 2 atmospheres preserved the highest vitamin C content, as well as the individual carotenoids. The wound-induced phenolic compounds, mainly trans chlorogenic acid, increased two fold in baby carrots stored under 5 kPa O 2 + 5 kPa CO 2 . In general, CA maintained the overall visual quality of baby carrots up to 8 days. Controlled atmosphere of 5 kPa O 2 + 5 kPa CO 2 can be recommended as an optimum atmosphere to maintain quality of baby carrots, increasing bioactive compounds such as chlorogenic acid and avoiding anaerobic fermentation in case of temperature abuse.