Changes in biochemical characteristics related to firmness during fruit development of pepper (Capsicum annuum L.)

Five pepper (Capsicum annuum L.) lines with varying degrees in flesh firmness were used to identify biochemical characteristics related to fruit softening. Firmness of fruit flesh (with epidermis attached) and flesh (without epidermis) was measured at different developmental stages: premature [15-20 days post-anthesis (DPA), stage 1], green mature (commercially ripe, 30-35 DPA, stage 2), colour turning (fruit becoming 30-40% red, 40-50 DPA, stage 3), and red ripe (fruit totally red, 60-70 DPA, stage 4). Since firmness with and without the epidermis attached changed similarly in all pepper lines during development, flesh firmness (without the epidermis) was used to represent pepper fruit firmness. Biochemical characteristics measured included insoluble pectin, soluble pectin, and cellulose contents, and the activities of pectin methyl-esterase (PME), polygalacturonase (PG), beta-galactosidase, and cellulase. in all lines, flesh firmness was highest at stage 3, and then decreased during development. Soluble pectin content also increased in all lines. Cellulose content normally decreased after stage 3, but these changes varied among lines. With ripening PG and PME decreased in the most firm lines, and cellulase and beta-galactosidase were the key enzymes involved in the less firm lines. These biochemical characters related to fruit firmness and firmness type should provide for breeding for improvements in storage and transportation.