Preharvest spraying with L-Phenylalanine effectively delayed the degradation of chlorophyll in postharvest broccoli

L-Phenylalanine (L-Phe) is a biologically active aromatic amino acid that improves storage quality and disease resistance in fruit and vegetables. However, the effects of preharvest L-Phe treatment on storage traits of vegetables have not been reported. This study investigated the yellowing and chlorophyll metabolism of preharvested broccoli treated with L-Phe at different concentrations during storage. The results showed that L-Phe at 2 mmol L−1 preharvest spraying 7 d before harvest was effective in delaying the yellowing of broccoli florets during storage, and maintained higher levels in total chlorophylls, chlorophyll a and chlorophyll b and reduced the activities in broccoli florets of chlorophyllase (CLH), Mg-dechelatase (MDcase), pheophyllase (PPH) and pheophyllase a oxygenase (PAO). Further studies showed that the expression levels of genes associated with chlorophyll degradation such as chlorophyll b reductase (BoNYC1), chlorophyllase1 (BoCLH1), chlorophyllase2 (BoCLH2), pheophytinase (BoPPH) and pheophorbide a oxygenase (BoPAO) were significantly down-regulated by preharvest L-Phe treatment. Correlation analysis showed that total chlorophylls content was significantly and positively correlated with the H* value, hardness, chlorophylls a, b and BoSGR gene expression, and significantly and negatively correlated with the L*, a*, b* values, weight loss, MDcase enzyme activity, PAO enzyme activity and BoCLH2 gene expression (p < 0.05). The findings suggested that L-Phe preharvest treatment delayed broccoli yellowing through decreasing chlorophyll degradation.