Abstract
Abstract The penetration of Ca through apple (Malus domestica Borkh) fruit cuticles was investigated using isolated cuticles. Permeability coefficients (P) and diffusion coefficients (D) were determined from self-diffusion measurements (0.1 mm CaC12) in a permeability apparatus. It was demonstrated that the apple fruit cuticles carry fixed charges with an isoelectric point of 2.1 and that Ca can penetrate into fruit directly across the fruit cuticle. Intraspecific variability was high, which is typical of cuticular permeability (P = 1.852 × 10−6 cm·s−1, sd = 1.29; D = 13.830 × 10−11 cm2·s−1, sd = 7.72, at pH 8). The permeability coefficient increased with increasing pH; this result was confirmed with isolated tomato fruit cuticles that revealed a lower permeability (P = 0.253 × 10−6 cm·s−1; sd = 0.12; D = 3.502 × 10−11 cm2·s−1, sd = 1.12, at pH 8). The permeability increased to a value about four times greater after the extraction of soluble cuticular lipids. There appears to be a direct relationship between cuticular sorption and penetration.
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