Morphologic changes of starch granules in the apple cv. Mutsu during ripening and storage

Abstract

AbstractUnripe (A), semiripe (B), and ripe (C) apples (Malus domestica cv. Mutsu) stored (2–4 °C, 90–95% RH) for 1 week were studied. The decrease in the starch content was as a function of storage time and ripeness.The size (area, perimeter and circularity) of starch granules was determined by image analyzer (Semper6, Synoptics) interfaced with a standard light microscope (Olympus, BH2) using a bright field illumination. Area (Ar) (larger than 100 pixel), perimeter (Pe), and circularity (Ci) of the granules were measured. The distribution of Ar, Pe, and Ci was calculated by the Distribution Fitting Statistical program; normality of frequency distribution of data (Chi‐square test), average ± standard deviation, t‐values were presented. All data were analyzed by principal component analysis.Area and perimeter decreased, circularity increased with the storage time and ripeness. Critical differences were observed in the semiripe apple cortex (CoB0) and the ripe apple skin (SC0) compared with the other samples (unripe skin and cortex) at the harvest. In both samples, most starch granules swelled (19–24%), and the starch contents were significantly less than in others. The stage of ripeness could be more exactly followed by image analysis than by the starch iodine test, or the color of apple skin.The ultrastructure (SEM) of starch did show typical changes as a function of storage time. More smaller starch granules could be seen in the stored apples than in the fresh ones. Damaged (pits, cavities) starch granules were found in all samples.Carbon‐13 NMR spectra of isolated apple cortex starch were obtained with cross polarization (CP), magic angle spinning (MAS), and high power proton irradiation (HD). There were shoulders on the C‐1 resonance and on the C‐2, 3, 4, 5 cluster. These shoulders indicate the presence of amorphous starch.