The role of polysaccharides in apple firmness

As part of the Nova2Cidre joint research unit with the IFPC (Institut Français des Productions Cidricoles), work is underway to understand the origin of variability in the suitability of cider apples for pressing.

Understanding the variability of batches of apples involves gaining a better understanding of the complex factors associated with mechanical properties at different scales linked, on the one hand, to the assembly of polysaccharides making up the cell walls of apple tissues and, on the other, to the flow of fluids in the grating, at the scale of the tissue and the cell wall subjected to deformation during the process.

The firmness of six varieties of apples measured in the fresh state and after destructuring by freezing/thawing revealed distinct rheological behaviour depending on the variety.

Chemical analysis of the polysaccharides that make up the walls revealed fine pectin structures that contribute positively or negatively to firmness. In addition, the measurement of structural and dynamic parameters by nuclear magnetic resonance (NMR) showed that the crystalline organisation of cellulose was not linked to firmness and that the less organised the cellulose fibres were within the walls (faster relaxation), the more hydrated the pectins were (slower diffusion) and the firmer the fruit.