Fruit and Vegetable Texture: Role of Their Cell Walls

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Texture refers to a group of physical properties derived from the structural elements of the food and mainly related to the deformation, disintegration and flow of the food under a force. In plant-derived foods, such as fruit and vegetables, firmness and juiciness are the most important textural parameters. These properties depend on the cell shape and size, cell wall thickness and composition, adhesion between adjacent cells, and cell turgor. During ripening, fleshy fruit undergo a softening process that makes fruit palatable for consumption. However, oversoftening reduces fruit quality and leads to postharvest losses. The disassembly of parenchyma cell walls and the dissolution of the middle lamella are the main factors involved in fruit softening. Hemicellulose depolymerization and pectin solubilization and depolymerization are general events in the ripening of many fruit. The suppression of genes encoding pectin degrading enzymes, such as polygalacturonase or pectate lyase, reduces softening and extends postharvest shelf life in fruit of contrasting firmness. Vegetables not derived from fruit tissues generally are firmer and undergo less softening than fruit. Textural changes in vegetables are also related to alterations of the cell wall composition, although to a lesser extent than in fruit, and the loss of cell turgor due to transpirational water loss and leakage of osmotic solutes.