关键词: 苹果；质地；细胞壁多糖；果胶结构；原子力显微镜

Abstract: In this study, ‘Gala’, ‘Golden Dwarf’, and ‘Starking’ apples harvested at the mature stage were used as experimental materials to analyze the potential relationship between texture quality and cell wall polysaccharide contents. The structural differences in water-soluble pectin (WSP), chelating-soluble pectin (CSP), and sodium carbonate-soluble pectin (SSP) in the three cultivars were studied using atomic force microscopy (AFM). The results showed that the texture properties such as hardness, brittleness, chewiness, gumminess, and the contents of cell wall polysaccharides including starch, protopectin, WSP, CSP, SSP, cellulose, hemicellulose, and lignin in “Starking’ apple peel were higher than those of ‘Golden Dwarf’ apple peel. The contents of SSP, cellulose, and hemicellulose in ‘Gala’ apple pulp were higher than those in ‘Golden Dwarf’ apple pulp, which had lower hardness and brittleness, and the contents of protopectin and starch in the pulp were significantly higher than those in the peel. Correlation analysis showed that the hardness of the peel and pulp was significantly positively correlated with the contents of SSP, hemicellulose, and cellulose, and the hardness of the peel was significantly positively correlated with the chain height and width of SSP. AFM images revealed that WSP, CSP, and SSP in the three cultivars​ exhibited aggregate, branched, and dendritic structures, with significant structural differences among them. The size of WSP and CSP aggregates, pectin particle size, WSP chain height (> 375 nm), and chain width (> 800 nm) frequencies were higher in ‘Gala’ and ‘Starking’ apple peels than in ‘Golden Dwarf’ apple peel. The structure of SSP in all three cultivars was dendritic, while many disordered, intact long-chain structures surrounded the SSP major chain in ‘Gala’ apple peel and pulp. In contrast, the structure of SSP in ‘Golden Dwarf’ apple peel and pulp exhibited numerous short spike-like side chains around the major chain, and the structure of SSP in ‘Gala’ apple pulp contained more linear long chains and dense branched side chains. In summary, the content of cell wall polysaccharides and the structure of pectin are closely related to texture characteristics. Apple cultivars with higher cell wall polysaccharide contents and higher frequency of long-chain, wide-chain WSP, CSP and SSP may possess superior texture quality. These findings can provide data support for the appropriate storage of apples and the quality improvement of processed products, thus facilitating the specialization of apple varieties for processing.

Key words: apple; texture; cell wall polysaccharides; pectin structure; atomic force microscopy