Effect of Calcium Chloride on Quality and γ-Aminobutyric Acid Metabolism of Fresh-Cut Lettuce

The effects of calcium chloride treatments on the storage quality and γ-aminobutyric acid (GABA) metabolism of fresh-cut lettuce were studied. Fresh-cut lettuce shreds were treated with 0%, 0.5%, 1.0%, 1.5% or 2.0% calcium chloride solution for 10 min and stored at 10 ℃ for 48 h. The quality parameters and GABA content were measured to determine the optimum treatment conditions and the mechanism by which calcium regulates GABA synthesis. The results showed that calcium chloride at different concentrations delayed the increase of mass loss rate, aerobic plate count and browning index, retarded the decrease of ascorbic acid and chlorophyll contents, and promoted GABA accumulation in fresh-cut lettuce, with 1.0% calcium chloride treatment being most effective in delaying the quality deterioration and promoting GABA synthesis. Furthermore, calcium chloride treatment increased the activities of glutamate decarboxylase (GAD), diamine oxidase (DAO), polyamine oxidase (PAO) and 4-aminobutyraldehyde dehydrogenase (AMADH), and promoted the decomposition of glutamic acid and polyamine, thus inducing the formation of GABA in fresh-cut lettuce. These results indicated that calcium chloride treatment could not only effectively maintain the quality, but also promote the synthesis of GABA and improve the nutritional value of fresh-cut lettuce during storage.