EVALUATION OF THE PHYSIOLOGICAL RESPONSE OF SHREDDED GALEGA KALE UNDER LOW OXYGEN AND HIGH CARBON DIOXIDE CONCENTRATIONS

Abstract

The high perishability of fresh-cut products requires the use of preservation techniques along the distribution chain. Refrigeration and modified atmosphere packaging (MAP) are important postharvest techniques in the extension of produce shelf life. Shredded Galega kale (Brassica oleracea var. acephala) is a fresh-cut vegetable of special interest in the Portuguese market. Potential benefits and risks of low O2 and high CO2 concentrations in fresh shredded Galega kale should be addressed before the commercial application of MAP. Respiration rate, sensory attributes, and colour alterations, in addition to water, chlorophyll, and ascorbic acid contents were monitored in shredded Galega kale during storage at 20 °C under different atmospheres. Low O2 tolerance (1, 2, 3 or 21% v/v O2 without CO2) was tested and it was concluded that quality retention improved with reduced O2 concentration and no induction of anaerobic respiration was detected. High CO2 tolerance (0, 10, 15, or 20% v/v CO2 plus 21% v/v O2) was also tested. Storage under high CO2 concentration extended the product shelf life and no symptoms of CO2 injury were detected. Finally, combinations of low O2 and high CO2 (1 or 2% v/v O2 plus 15 or 20% v/v CO2 and air as control) were analysed. No differences were observed among the different concentrations tested in this range. An atmosphere of 1-2% v/v O2 plus 15-20% v/v CO2 will extend the shelf life of shredded Galega kale at 20 °C to 4 days, compared to 2 days in air storage. OBJECTIVES The selection of concentrations of O2 and CO2 that prolong the shelf life of a given fresh product is essential to design a successful MAP system. No research has yet demonstrated a beneficial effect of reduced O2 and elevated CO2 on fresh shredded Galega kale quality. The specific objectives of this work were: i) to evaluate the tolerance of fresh shredded Galega kale to low O2 levels and to high CO2 levels, and ii) to identify a range of O2 and CO2 adequate for MAP of this product.