EFFECT OF ARGON-ENRICHED ATMOSPHERES ON SHELF LIFE OF FRESH-CUT 'ICEBERG' LETTUCE

The objective of this study was to evaluate the effect of Ar-enriched atmospheres, on the maintenance of quality characteristics of fresh-cut lettuce during refrigerated storage. ‘Iceberg’ lettuce was processed according to industry procedures and stored in a humidified flow of air (as a control) and of the following atmosphere: 97% Ar + 3% O₂, 50% Ar + 3 % O₂, (balanced with 47% of N₂), and 97% N₂ + 3% O₂. Samples were stored at 5°C and evaluated before and after 2 and 9 days of storage. All atmospheres were effective in slowing down respiration rate at 9 days, whereas no significant difference in color, texture, flavor, phenols, antioxidant activity, acetaldehyde and ethanol content were observed. After 9 days of storage, lettuce stored in 50% Ar and in N₂ atmosphere showed lower PPO activity than control, whereas samples stored under 97% Ar-enriched atmosphere exhibited an intermediate value. On the other hand, samples stored in 50% Ar-enriched atmospheres and control samples showed a higher cut edge discoloration, compared to samples stored in N₂ atmosphere, whereas sample stored in 97% Ar showed intermediate value. Moreover, lettuce stored in 97% Ar best retained ascorbic acid content up to 2 days of storage, but no differences among treatments were detected at the end of storage. At this time samples stored in N₂ atmosphere showed the lowest mesophilic load, whereas both 97% Ar and 97% N₂ were effective in slowing down yeast and mould. Our results suggest that the effects of argon-enriched atmosphere are quite similar to that of nitrogen, with a lower control of mesophilic bacteria and a better retention of vitamin C. Further investigations are needed to propose argon as an alternative gas in modified atmosphere packaging of fresh-cut lettuce.