Abstract

According to the physical properties of leaf lettuce and its heat and mass transfer mechanism in vacuum pre-cooling process, the pre-cooling temperature, pressure and volume of spray-applied water were verified throughout the experiment. The key factors affecting the water removal and storage quality of leaf lettuce during vacuum pre-cooling were the water volume and pre-cooling pressure. The quantities of water tested were equal to 4.21–5.98% of the total sample mass and the mass loss of the sample was 1.99–2.87%. Under pre-cooling pressure of 600, 1000 and 1500 Pa, the mass loss was 2.76, 2.70 and 1.93%, respectively. The optimum quantity of the spray-applied water was 5% of the total sample mass.