Extending the shelf life and qualities of baby cos lettuce using commercial precooling systems

Abstract

Due to a limited shelf life, baby cos lettuce lasts for only a few days after arriving at a market destination. At the present time, no research is conducted on what impacts of commercial precooling systems have on physico-chemical qualities and ultrastructure of this crop. The study provides understanding of the cellular senescence, especially associated with chloroplast and vacuole which directly affect the produce’s greenness and freshness. This research was conducted to investigate the optimum parameters for vacuum cooling, and the effects of different commercial precooling systems (room cooling, forced-air cooling, and vacuum cooling) on the physico-chemical qualities, bioactive compounds and ultrastructure of baby cos lettuce during storage at 4 °C. Overall, vacuum cooling at 0.6 kPa holding pressure and 25 min holding time maintained significantly (P ≤ 0.05) better produce qualities than forced-air cooling at 1.4 m s−1 air velocity or room cooling at 0.65 m s−1. A significant increase in total phenolics content was detected in all samples, with antioxidant activity also increasing significantly until seven days of storage for samples precooled by vacuum cooling, and until nine days of storage for samples precooled by forced-air cooling, room cooling, and in the non-precooled sample, decreasing thereafter. However, both antioxidant activity and phenolics content were better retained during storage in samples precooled by vacuum cooling. Although gradual declines in ascorbic acid and total chlorophyll content were observed across all treatments, cells of baby cos lettuce precooled via forced-air or room cooling and those in the control sample exhibited chlorophyll degradation (according to TEM), resulting in a diminished green colour. This study thus demonstrates that vacuum cooling is effective in prolonging the shelf life of baby cos lettuce grown in Chiang Mai, Thailand from nine to sixteen days at 4 °C and 85% RH, increasing the produce market window.