Comparison of industrial precooling systems for minimally processed baby spinach

• Precooling benefits the quality and shelf life of baby spinach in spring.
• Hydro cooling and vacuum cooling increase the water content and the colour of the leaves.
• Vacuum cooling reduces the visual quality because of the increase in the tissue damage.
• Specific tests to optimise vacuum cooling process are needed to prevent tissue damage.

Leafy greens including baby spinach are particularly prone to rapid dehydration. After harvest, leafy greens should be refrigerated as soon as possible to remove the heat from the field in order to decrease respiration rate and increase shelf-life. Delays between harvest and cooling should be avoided, especially during warm weather to avoid water loss. There is a wide range of precooling systems available for using in fresh produce. However, the best precooling system for baby leaves as raw material for the fresh-cut industry has not been well established. The aim of this study was to compare four precooling systems including room cooling (RC), forced air cooling (FAC), hydro cooling (HC) and vacuum cooling (VC) for their effects on quality and shelf-life of baby spinach. Two separate trials, one in winter and another in spring were carried out. Leaf water content increased after cooling in HC and VC but more significantly in winter while in spring, differences among treatments were not significant. The colour measured as chroma was more vivid in HC and VC just after processing but after storage, no differences among precooling treatments were observed. In winter, there were no significant differences in the respiration rate among precooling systems. However, in spring, HC and VC decreased respiration rate and modified less the headspace gas composition of the packages. Pseudomonas counts significantly decreased in HC and VC due probably to the washing effect of the leaf surface without promoting the growth of spoilage microorganisms. Surprisingly, visual quality was significantly lower in VC compared with the rest of precooling treatments due to the higher degree and number of damaged leaves. In conclusion, selection of the precooling system is critical during warm weather because of the high temperature at harvest. Hydro cooling is a good precooling system for baby spinach in spring as it decreases rapidly leaf temperature, decreasing respiration rate and extending shelf life. However, in winter, precooling systems are not as critical because the temperature at harvest was similar to the temperature reached after precooling.