Fresh-cut kale quality and shelf-life in relation to leaf maturity and storage temperature

Kale (Brassica oleracea var. acephala) is a very nutritious leafy vegetable and its consumption in fresh-cut salads has increased in recent years. Kale leaves may be harvested at different stages of maturity, resulting in a heterogeneity that may be detrimental to fresh-cut salad quality and shelf-life. Changes in composition and visual parameters were investigated in fresh-cut kale leaves ('Lacinato') harvested at three maturity stages used commercially based on leaf position and size (immature, mature, overmature), two temperatures (0 and 5 degrees C) and five periods of storage (0, 14, 21, and 28 days; up to 42 days at 0 degrees C). Product was cut manually into 2 cm strips, washed in chlorinated water, manually centrifuged, and packaged in unsealed LDPE bags. Total chlorophyll content decreased during storage, with the lowest concentrations found in pieces from overmature leaves at 5 degrees C, while the total carotenoid content did not vary among the conditions studied. Ammonia content, an indicator of protein breakdown and senescence, remained low for pieces from all maturity stages stored at 0 degrees C up to 42 days, was intermediate in immature cut leaves at 5 degrees C, and increased dramatically in pieces from mature and overmature leaves at 5 degrees C between 21 and 28 days. Objective color values as well as marketability indicators (off-odors, overall visual quality, yellowing, decay, cut-end browning) exhibited significant differences in response to the postharvest conditions studied. In general, the loss of composition and visual quality of fresh-cut kale leaves increased with increasing temperature, days of storage, and leaf maturity.