The effect of layer-by-layer edible coating on the shelf life and transcriptome of ‘Kosui’ Japanese pear fruit

Edible coatings attract much interest today as safe and effective techniques for maintaining quality and extending shelf life of fruit and vegetables. However, the underlying molecular mechanisms remain unclear. The aim of this study was to identify genes involved in enhancement of shelf life in ‘Kosui’ Japanese pear (Pyrus pyrifolia Nakai) fruit by chitosan/alginate-based layer-by-layer (LBL) edible coatings. Both tri-layer and penta-layer LBL coatings effectively minimized fruit respiration and ethylene production rates, inhibited flesh firmness loss, and prevented peel color change for 21 d at 20 °C but had little effect on weight loss. Gas permeability tests on polyethylene terephthalate films revealed that LBL coatings substantially lowered oxygen transmission rates but had little effect on water vapor transmission rate. In an attempt to identify the pathways involved, we monitored gene expression in LBL-coated and uncoated fruit by RNA-Seq analysis. This analysis revealed a clear downregulation of genes associated with ethylene production and fruit ripening, as well as the tricarboxylic acid cycle following application of LBL edible coating. On the other hand, genes associated with the glycolysis pathway were mostly upregulated. Together, these results indicate that prolonged shelf life by chitosan/alginate-based LBL edible coating could primarily result from control of the balance of aerobic-anaerobic metabolism.