Solid-state 13C NMR characterization of cell walls of ripening strawberries

Abstract

Ripe and unripe cell walls isolated from the cortical tissues of strawberry (Fragaria × ananassa Duchesne cv. Yolo) using HEPES-buffered phenol of pH 6.5 were analysed using solid-state 13C nuclear magnetic resonance. Changes in cell wall components during ripening were investigated by separating the spectra, using proton spin relaxation editing, into three subspectra based on the mobility of the molecules. The subspectra can be assigned to rigid material (cellulose), semirigid components (primarily polygalacturonic acid) and semimobile (other detectable noncellulosic substances). The results show that, with ripening, separation between the semirigid and semimobile domains became more distinct. Associated with this, the ratio of noncellulosic material (i.e., pectins and hemicelluloses) to rigid cellulose decreased from 2.3 for unripe to 1.9 for ripe. The crystallinity of the cellulose molecules remained unaltered throughout ripening. Furthermore, our work indicates that the basic cellulose crystallite of strawberry cell walls appeared exceptionally small compared with other systems studied thus far. Key words: solid-state CP-MAS 13C NMR, cellulose, plant cell walls, strawberry, fruit ripening.