Starch degradation and starch pattern indices; interpretation and relationship to maturity

Abstract

Abstract Indication of starch hydrolysis by iodine staining is widely used in determining when to harvest apples, yet few quantitative changes in apple starch have been reported and no reports relate these to changes in iodine staining. Starch accumulation and degradation during fruit development was examined in ‘Fuji’ and ‘Royal Gala’ apples. Both cultivars displayed similar patterns in starch accumulation and degradation. Starch concentrations decreased until 30 days after anthesis, then increased, peaking at 100 days after anthesis. Starch concentrations differed between the tissue zones, being highest in the outer cortex and lowest in the core. Net starch degradation started at the same time in all tissues, well before iodine stain clearing was detected in the core, and before there was any change in background colour or increase in ethylene production. Iodine stain clearing occurred once starch concentrations fell below 2–3 mg g/fwt. The rate of degradation was slower in the core than in the outer cortex and other tissues in both cultivars, and in ‘Fuji’ fruit the rate of degradation in the vascular bundles was also slower than in the outer cortex. The rate of starch degradation differed also between the two cultivars, leading to an apparent difference in timing of starch degradation according to starch pattern indices. Application of these results to fruit maturing under different conditions may lead to better interpretations of inherent fruit quality at harvest.