Integration of cell wall fraction, organic matter content, and membrane to understand crispness changes in apples

Abstract

Crispness is a crucial commercially property of the apple fruit texture, but the dynamic change of apple crispness and contributing factors during fruit development and storage remain poorly understood. In this study, we examined the crispness of ‘Hanfu’ apples from fruitlet to senescence and analyzed the physiological and biochemical indexes involved in crispness change. The results indicate that ‘Hanfu’ apples exhibited the lowest crispness at 98 days after full bloom (DAFB), then gradually reached the highest crispness at 178 DAFB, followed by a decrease during storage. Crispy fruit features large cells and low contents of cell wall material, cellulose, and hemicellulose, which reduces the cell wall resistance. High sugar and low hydrogen peroxide (H2O2) contents improve the cell turgor and membrane stability. At the molecular level, the relative expression of genes associated with cell wall expansion (MdEXPA2), water transport (MdPIP1;3), and sugar accumulation (MdHK2) was significantly low level at 178 DAFB, whereas genes related to membrane stability maintained a relatively high expression level. This outcome may be linked to cell wall swelling, sugar accumulation, and rapid reactive oxygen species scavenging at 178 DAFB. Therefore, apple crispness depends on cell wall fractions, organic matter content, and membrane stability rather than a specific cell component. The results of this study provide a foundation for the improvement of the fruit quality, and postharvest management strategies.