SORPTION AND DIFFUSION OF AN ETHOXYLATED STEARIC ALCOHOL AND AN ETHOXYLATED STEARIC AMINE INTO AND THROUGH ISOLATED PLANT CUTICLES

Sorption and transfer of an ethoxylated stearic alcohol and an ethoxyl ated stearic amine into and through plant cuticles were investigated u sing enzymatically isolated tomato and pepper fruit cuticles. Sorption was rapid during the first hour and equilibrium was nearly achieved w ithin 48 hours for amine and 72 hours for alcohol. Sorption was greate r for the alcohol and there was a relatively small difference between the two plant species. Cuticle/water partition coefficients (K-cw) det ermined at two surfactant concentrations (0.1 and 1 mM) were greater a t the lower concentration. K values for alcohol were 239 and 205 at 0. 1 mM, and 84 and 88 at 1 mM for tomato and pepper, respectively. Desor ption of both surfactants from cuticles during washing with water was very slow and was not complete. After 3 hours washing, 81% and 85% of amine, and 85% and 87% of alcohol were still retained by tomato and pe pper fruit cuticles, respectively. Transfer measurements through cutic les expressed by flux measurements and permeability coefficients (P) s howed that the surfactant penetration increased linearly in relation t o lime after a steady state was reached; the linear regression coeffic ient was generally between 0.98 and 1 for individual measurements. The transfer was more rapid for alcohol for the three tested concentratio ns (0.1, 1 and 5 mM). For pepper cuticles, the difference observed bet ween the two surfactants was greater at the lower concentration. Data obtained were used to calculate diffusion coefficients (D) both from f lux measurements and hold-up times. Diffusion was greater for alcohol which means that this surfactant has a better mobility than amine with in cuticles. Thus, cuticular permeability to the two surfactants was q uantitatively analysed with the determination of the three characteris tic parameters : P, K and D. (C) 1997 Elsevier Science Ltd.