Fruit ripening, cell wall composition, and calcium associations in cranberry (Vaccinium macrocarpon Ait.) cultivars with contrasting firmness

• Fruit firmness increased during cranberry development, followed by a sharp decline at ripening. • Greater firmness loss in ‘BG’ during ripening was correlated with higher hemicellulose solubilization. • Fruit firmness and elasticity are positively correlated to chelate-soluble pectin content and cell wall Ca. • Differences in pectin and hemicellulose solubilization between cultivars were influenced by cell wall Ca concentration. In cranberry ( Vaccinium macrocarpon Ait.), fruit firmness is a critical quality trait for postharvest life and the production of high-value products such as sweetened dried cranberries (SDC), yet the physiological and biochemical mechanisms underlying this characteristic remain poorly understood. The objective of this study was to determine changes in cell wall composition and calcium (Ca) concentration throughout fruit development in two cranberry cultivars with contrasting fruit firmness (‘Stevens’ and ‘BG’). Fruit samples were collected from 14 to 91 days after full bloom (DAFB) and assessed for firmness, elasticity, size, fresh weight, anthocyanin concentration, and internal structure. Cell wall composition was analyzed for water-soluble pectin (WSP), CDTA (trans-1,2-cyclohexanediamine tetraacetic acid)-soluble pectin (CPS), Na₂CO₃-soluble pectin (SSP), and 1 M and 4 M KOH hemicellulose fractions alongside Ca concentrations in both total fruit and in the cell wall. At 91 DAFB, ‘Stevens’ had a higher firmness than ‘BG’, which was correlated with greater CSP concentration and higher levels of cell wall-bound Ca. In contrast, ‘BG’ exhibited a sharper firmness decline during ripening, associated with increased solubilization of tightly bound hemicellulose (4KOH fraction) and lower cell wall-bound Ca concentration. Our findings highlight the role of Ca in the solubilization of pectin and hemicellulose during fruit development, maintaining fruit firmness and elasticity offering new insights for improving cranberry quality and fruit processing.