Cell wall metabolism in cold-stored ‘Somerset’ sweet cherry fruit

'Somerset' is a dark-red, sweet cherry (Prunus avium L.) cultivar displaying remarkable firmness levels, with concomitantly longer shelf-life potential in comparison to other varieties. It is generally accepted that fruit firmness depends mainly on the composition, structure and interconnections among cell wall polysaccharides. However, the biochemical mechanisms involved in cell wall disassembly vary widely among species, and the understanding of the processes underlying firmness loss in cherry fruit is particularly poor, although a critical role for β-galactosidase (β-Gal) activity has been suggested. In this study, 'Somerset' fruit were hand-collected at commercial maturity, and kept at 0 oC for 14 or 28 days plus 3 additional days at 20 oC to simulate commercial shelf life. Firmness, weight loss and juiciness were assessed in each case as indicators of fruit texture. Soluble and insoluble cell wall materials were extracted from lyophilized tissue, and a number of cell wall-modifying enzyme activities were also assessed therein. While β-xylosidase (β-Xyl), α-L-arabinofuranosidase (AFase) and pectin methylesterase (PME) activities were apparently connected to ripening-related firmness changes in this cherry cultivar, data obtained do not support a role for β-Gal in this process.