Studies on Octylphenoxy Surfactants 1: III. Sorption of Triton X-100 by Isolated Tomato Fruit Cuticles

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Sorption characteristics of a polyethoxy (EO) derivative of octylphenol (OP) were determined for enzymically isolated mature tomato (Lycopersicon esculentum Mill. cv Sprinter) fruit cuticles at 25°C. Sorption was followed using 14C-labeled OP + 9.5EO (Triton X-100). Solution pH (2.2-6.2) did not affect surfactant sorption by tomato fruit cuticular membranes (CM). Surfactant concentration (0.001-1.0%, w/v) had a marked impact on sorption. Sorption equilibrium was reached in 24 hours for OP + 9.5EO concentrations below the critical micelle concentration (CMC), whereas 72 to 120 hours were required to reach equilibrium with concentrations greater than the CMC. Regardless of when equilibrium was attained, initial sorption of OP + 9.5EO occurred rapidly. Partition coefficients (K) of approximately 300 were obtained at pre-CMC concentrations, whereas at the highest concentration (1.0%), K values were approximately 15- to 20-fold lower. Sorption was higher for dewaxed CM (DCM) than for CM. At OP + 9.5EO concentrations below the CMC, the amount (millimoles per kilogram) sorbed by CM and DCM increased sharply as the CMC was reached. After an apparent plateau in the amount sorbed at concentrations immediately below and above the CMC, sorption by CM and DCM increased dramatically with OP + 9.5EO concentrations greater than the CMC (0.5 and 1.0%). In contrast, sorption of OP + 5EO (Triton X-45) by CM and DCM differed from one another at relatively high (0.5 and 1.0%) concentrations, where sorption by DCM increased with increasing concentration, but plateaued for the CM. Sorption of OP + 9.5EO was also related to CM concentration, with an inverse relationship existing between sorption and CM at concentrations less than 3.33 milligrams per milliliter.

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