Gene Expression Analyses Reveal Mechanisms of Inhibited Yellowing by Applying Selenium-Chitosan on Fresh-Cut Broccoli

The yellowing of green broccoli is a phenomenon that indicates a serious deterioration of freshness. The green broccoli has been more popular than the yellow one, with its higher nutritional value. Chitosan coating has been employed in vegetables for green-keeping, owing to its functions of regulating chlorophyll metabolism and antioxidant defense. Furthermore, selenium was commonly utilized in the pre-harvest of fruit and vegetables as an antioxidant and chlorophyll regulator. However, there have not yet been concerns about the effects of selenium-chitosan on vegetable yellowing. This study first investigated the impact of selenium-chitosan on the quality of fresh-cut broccoli yellowing during storage by analyzing the chromatic aberration and phytochromes. Additionally, then, the gene expression related to chlorophyll metabolism (POR, CAO, HO, CHLI, NYC1), carotenoid metabolism (VDE, CCS, LCYE, ZEP, HYD), and transcription factors (NAC92, ZIPPER, bHLH66, APL, PIF4) were analyzed using the RT-qPCR technique. Test results showed that treatment with selenium-chitosan can slow down the reduction in h° (Hue angle values) and reduce ethylene release rate and respiration intensity. Via the molecular approach, it was further identified that this treatment could inhibit chlorophyll degradation and carotenoid biosynthesis, accompanied by lower expression levels of heme oxygenase (HO), chlorophyllide A oxygenase (CAO), violaxanthin de-epoxidase (VDE), β-carotene 3-hydroxylase (HYD), NAC92, basic leucine zipper (ZIPPER), bHLH66, PIF4 and APL, and higher expression levels of magnesium chelatase subunit I (CHLI) and lycopene ε-cyclase (LCYE) genes. This work can be used to explore the molecular mechanism of selenium-chitosan in inhibiting the yellowing of fresh-cut broccoli. This study will be of great economic importance in marketing and export by increasing the shelf life of fruits and vegetables.