Electron-beam generated X-ray irradiation treatment alleviates fruit-body softening of harvested Hericium erinaceus by regulating metabolisms of membrane lipid and cell wall

Fresh Hericium erinaceus is susceptible to softening after harvest, 1.0 kGy electron-beam generated X-ray (EBGX) irradiation could alleviate this phenomenon. To clarify the possible mechanism of EBGX regulated the softening of H. erinaceus, we explored its effects on membrane lipid and cell wall metabolism. Results showed that 1.0 kGy irradiation enhanced cell membrane stability, as evidenced by higher levels of phosphatidic acid, phosphatidylcholine, phosphatidylinositol, and the ratio of unsaturated fatty acids to saturated fatty acids (U/S), whereas lower levels of ROS, lipoxygenase, phospholipase D, and lipase activities compared to the control. More importantly, 1.0 kGy-treated samples exhibited a minimum of chitinase (4.12 U mg- 1), cellulase (16.34 U mg- 1), beta-glucanase (13.28 U mg- 1), and PAL (10.17 U mg- 1) activities at 9d, but retained higher chitin, cellulose, beta-glucan, and lignin contents, thus suppressed the disassembly of cell wall structure. Utilizing comparative transcriptomic data, the differentially expressed genes (DEGs) from starch and sucrose metabolism, amino sugar and nucleotide sugar metabolism, and lipid degradation metabolism were related to softening in H. erinaceus with control or irradiation treatments. Additionally, the relative abundance of DEGs-related transcripts like HeLOX, HePLD, HeLPS, HeCHI, HeCEL, HeGLU1, HeGLU2, and HePAL were prominently downregulated in the irradiation treatment. Overall, 1.0 kGy EBGX irradiation could retard the postharvest softening process of H. erinaceus by regulating the gene expression of membrane lipids and cell wall metabolic pathways.