Inhibitory Effects of CaCl2 and Pectin Methylesterase on Fruit Softening of Raspberry during Cold Storage

Quality of raspberry fruit experiences a rapid decline after harvest due to its vulnerable texture and high moisture content. Application of calcium chloride (CaCl2) combined with pectin methylesterase (PME) is efficient in delaying fruit softening. In this study, the effects of exogenous CaCl2 alone or in combination with PME on the structure of the cell wall, the molecular properties of pectin, and the amount of free water of raspberry during postharvest storage were investigated. The results showed that CaCl2 combined with PME treatment could maintain fruit firmness and inhibit weight loss. The treatment of CaCl2+PME maintained the cell wall structure via sustaining middle lamella integrity and reducing the activities of cell wall-degrading enzymes, such as polygalacturonase, pectin methylesterase, β-galactosidase, α-L-arabinofuranosidase, and β-xylosidase. In addition, CaCl2+PME treatment could effectively increase the content of chelate-soluble pectin (CSP) and develop a cross-linked structure between Ca2+ and CSP. Moreover, CaCl2+PME treatment was of benefit in maintaining free water content. CaCl2 in combination with PME treatment could be a promising method for inhibiting softening and maintaining the quality of postharvest raspberry during cold storage.