Internal atmosphere composition and skin permeance to gases of pepper fruit

Characterisation of internal atmosphere composition offers the potential to explain variability in responses of horticultural crops to modified atmosp here treatments and to quantify permeance of fruit skins to the respiratory gases. In this paper, the theoretical basis by which fruit skin permeance can be calculated from other gas exchange variables is presented. Surface c hambers close to equilibrium with the fruit's internal atmosphere were used to monitor internal atmosphere composition of sweet pepper (Capsicum annum , cv. Reflex). Physical equilibration of chamber contents over wounded frui t surface was essentially complete in less than 4 h. However, physiological drift in internal atmosphere composition meant that substantial changes co ntinued to develop over more extensive periods. Removal of cuticle beneath the chamber was shown to be essential for equilibration of chamber contents within physiologically meaningful periods. Samples of atmosphere removed d estructively from the fruit cavity consistently contained more O-2 but less CO2 than samples similarly removed from the fruit flesh. Levels of CO2 wer e higher in samples removed directly from the flesh by syringe than in thos e taken from surface chambers, indicating potential for an effect of the va cuum used to take direct removal samples on sample composition. Permeance o f pepper cuticle to CO, was about ten times greater than that to O-2 (simil ar to 244 and 24 pmols(-1)m(-2) per Pa, respectively). Removal of cuticle d ramatically increased permeance of the fruit surface and hastened equilibra tion of surface chambers with the fruit's internal atmosphere. Surface cham bers adhered over fruit surface from which the cuticle has been removed wou ld be the most reliable means to assess composition of the atmosphere in im mediate contact with the cells of pepper tissue. (C) 2000 Elsevier Science B.V. All rights reserved.