Effect of hypobaric packaging on respiration and quality of strawberry and curled lettuce

The potential of hypobaric packaging in rigid small containers to reduce respiration and enhance freshness and keeping quality was tested for strawberry and curled lettuce. To study the effect of hypobaric conditions on respiration rate, respiration kinetics applicable to hypobaric conditions were characterised as a function of oxygen and carbon dioxide concentrations. Different hypobaric conditions of 25.3, 50.7, and 76.0 kPa (0.25, 0.5, and 0.75 atm, respectively) were applied to storing and packaging the two commodities at 3 °C with intermittent fresh air flushing and vacuum treatment to avoid creating an anoxic environment. The treatments were compared with control storage conditions of 101.3 kPa (1 atm). Reduced oxygen and/or slightly raised carbon dioxide concentrations created by the hypobaric treatment were analysed for their effect on respiration in terms of oxygen consumption and carbon dioxide production. More rigorous hypobaric conditions resulted in lower respiration rates for both commodities tested. However, there was an operational drawback with the most severe condition of 25.3 kPa in that fresh air flushing and repetitive vacuum application were required too frequently for the densely packed strawberry packages. With the leafy vegetable, curled lettuce, the severe conditions caused the quality defect of high moisture loss. Therefore, an intermediate hypobaric condition of 50.7 kPa was selected and tested for the long-term storage trials. It led to better retention of ascorbic acid and slightly retarded bacterial growth for strawberry fruit; however, curled lettuce suffered from high weight loss without any noticeable benefit in keeping quality under the same condition.