Mechanism of high humidity hot air impingement blanching (HHAIB) on drying and quality characteristics of apple slices: from macroscopic to cell wall and molecular levels

High humidity hot air impingement blanching (HHAIB) is a highly efficient thermal pretreatment technology for fruits. However, its application potential and underlying mechanism in apple processing remain unclear. This study investigated the effects of HHAIB on enzyme activity, drying characteristics and physicochemical properties of apples, with a specific focus on the changes in pectin polysaccharides. The results demonstrated that HHAIB significantly increased the content of water-soluble pectin (WSP), while remarkably reducing the contents of chelate-soluble pectin (CSP) and Na 2 CO 3 -soluble pectin (NSP). Additionally, the average molecular weight of WSP was increased, whereas that of NSP was decreased. Microscopic analysis revealed that HHAIB pretreatment gradually disrupted the integrity of cell membranes, and induced the degradation of the middle layer of cell walls and pectin. These microstructural changes directly impaired the integrity of cellular tissues, thereby accelerating the drying process and shortening the drying time by 19.4–43.9%. In terms of enzyme activity, blanching effectively inactivated peroxidase, which in turn improved the surface color of apple slices. Notably, apple slices treated with HHAIB for 50 seconds retained the highest levels of phenolics, flavonoids, and antioxidant activity. Consequently, this study provides valuable insights into the technological support for the application potential of thermal pretreatment in fruit processing.