Secondary metabolism associated with softening of shiitake mushroom (<i>Lentinula edodes</i>) induced by O₂ depletion and <scp>CO</scp>₂ accumulation

Abstract

Abstract It is difficult to preserve fresh shiitake mushroom ( Lentinula edodes (Berk.) sing) partly because of the rapid deterioration of texture (softening or lignification). In this study, we developed a storage model in which tissue softening was induced to analyse the relationship between changes in firmness and alterations in cell wall chemical components as well as their metabolism. The results showed that the treatment group accumulated more CO 2 and contained less O 2 because of the poorer permeability in package. The contents of glucan and chitin in the treatment group decreased from 241.3 ± 13.2 mg g −1 and 46.3 ± 1.2 mg g −1 to 157.3 ± 11.2 mg g −1 and 18.0 ± 1.0 mg g −1 ( P &lt; 0.05) with the accumulation of CO 2 . The activities of major cell wall degradation‐related enzymes were enhanced in the softening model, and the expression levels of major genes that encode enzymes related to cell wall degradation were upregulated. Our results suggested that the softening of shiitake mushrooms induced by high CO 2 was associated with the degradation of polysaccharides and glycosaminoglycan and that these changes were systematically regulated by alterations in the activities and expression levels of related enzymes and genes.