Contribution of cell wall-modifying enzymes to the texture of fleshy fruits. The example of apple

Abstract

The cell walls of fleshy fruits consist of polysaccharide assemblies (pectin, hemicelluloses and cellulose), the structure and interactions of which vary depending on the genetics of the fruit, and its stage and conditions of development. The establishment and the structural reorganization of the assemblies result from enzyme/protein consortia acting in muro. The texture of fleshy fruits is one of the major criteria for consumer choice. It impacts also postharvest routes and transformation processes. Disassembly of fruit cell wall polysaccharides largely induces textural changes during ripening but the precise role of each polysaccharide and each enzyme remains unclear. The changes of cell wall polysaccharides during fruit ripening have mainly emphasized a modulation of the fine chemical structure of pectins by hydrolases, lyases, and esterases. This restructuring also involves a reorganization of hemicelluloses by hydrolases/transglycosidases and a modulation of their interactions with the cellulose by non-catalytic proteins, such as expansin. Apple is the third most produced fruit in the world and has been the subject of studies about fruit quality. This paper presents some of the results to date about the enzymes/ /proteins involved in fruit ripening with particular emphasis on apple.