Dynamic Changes in Quality and Metabolites of Soft Kale Stored in Perforation-Mediated Modified Atmosphere Packaging

概要

Modified atmosphere packaging (MAP) is one of the most promising techniques that has been widely and successfully used to extend the shelf life of fresh vegetables and fruits by controlling the surrounding gas composition of products (Kader, 2002). The depleted O2 and elevated CO2 in MAP, derived from the respiration rate of the product and the gas permeability of the packaging film, can reduce the respiration rate of the fresh product (Zagory & Kader.1988). In recent years, the perforation-mediated MAP (PM-MAP) has proved to be an effective technology for packing high-respiring products due to the high gas exchange rates achieved. The use of perforation technology has optimized the limited permeability properties of traditional MAP films (Hussein, 2015).

Fresh kale is highly perishable after harvest, readily losing its green color as well as undergoing marked postharvest loss of bioactive compounds. This study aimed to examine the effect of three different micro-perforated packaging films with different oxygen transmission rate (OTR) on the overall appearance and bioactive compounds of intact kale. In addition, the metabolomics profile of soft kale leaf and stem associated with the three different OTR pouches were characterized during the 12 d storage period at 10 °C.

The micro-perforated pouches with different OTRs had a significant impact on the postharvest performance of kale leaf and stem during storage at 10 ºC for a period of 12 d under dark conditions. As shown in Figs. A, B, no gaseous (O2 and CO2) modification was observed within the OTR 1.66×106 pouch. As a consequence of the respiration of kale and the gradient-induced gas transmission characteristics of the packaging film (Zhang et al., 2015), the gaseous composition in the OTR 3×103 pouch modified to lie within the ranges of 1.9 ~ 7.4 % O2 and 8.5 ~ 9.6 % CO2, which are near the recommended internal atmospheres of 2~5 % O2 and 3~8 % CO2 in MAP for the preservation of fresh leafy vegetables to avoid the anaerobic respiration at low O2 atmosphere and to avoid the CO2 injury at high CO2 concentrations (Mampholo et al., 2013). The OTR 64 pouch showed significant increases in CO2 and decreases in O2 concentrations, with the O2 concentration decreasing to 0 % on day 6 and CO2 increasing to 23.3 % on day 12. Usually, a low O2 and/or a high CO2 atmosphere suppresses respiration rate, decreases ethylene production. However, the OTR 1.66×106 pouch showed a significantly (p < 0.05) lower concentration of ethylene throughout the storage period, which might be reflecting the high permeability of the packaging film used (Fig. C). The ethylene concentration in the OTR 3×103 pouch and OTR 64 pouch showed a sharp rise until day 6 and 9 day, respectively. As shown in Fig. C, the OTR 1.66×106 pouch, yellowing of kale leaves was recorded with a significantly (p < 0.05) lower h° value from day 6 onward. The overall evaluation of the effect on bioactive compounds of kale leaf showed that leaves stored in the OTR 3000 maintained the pigment concentrations (Figs. E, F); maximized the concentration of ascorbic acid (Fig. G), although it depressed the accumulation of the total polyphenols (Fig. H) during the postharvest storage. In addition, OPLS-DA showed 24.66% and 38.54% of the metabolites were contributed to the separation of the four class in leaf and stem, respectively (Figs, I, J). The middle OTR pouches (OTR 3000) located near from the fresh sample cluster and it showed little fluctuation compared with other two pouches. This result supported the fact that the micro-perforated pouch with an OTR of 3×103 mL m–2 d –1 atm–1 achieved the most promising storage effect on kale preservation.