Relationship between character of skin cover of coated pears and permeance to water vapour and gases

Pear fruit (Pyrus communis L.) with different skin characteristics (non-lignified: 'Bartlett','Doyenne du Comice' and 'Packham's Triumph'; or with lignified cells in the skin:'Beurre Bose') were treated at harvest with a carnauba-based wax emulsion at concentrations of 0, 5, 10, 20, 40, and 100% (v/v) of the commercial formulation to achieve different coating deposits on the skin and assessed for skin permeance at 20 degreesC and 60-70% RH. 'Bartlett' had the highest natural skin permeance to water vapour and gases, followed by 'Bosc','Comice' and 'Packham's'. Small increases in coating deposit on the skin substantially reduced permeance to H2O (P-H2O'), O-2 (P'(O2)) and CO2 (p'(CO2)) in cultivars with non-lignified skin, by improving coverage of cracks in the cuticle and blockage of lenticels. These cultivars also underwent a larger reduction in P'(O2) than P'(CO2) With increasing coating deposits. While 'Bartlett' and 'Comice' showed a more variable reduction in P'(O2) than in P'(CO2) With increases in coating deposit, the inverse was observed for 'Packham's'. 'Bosc', with lignified cells in the skin, had only small changes in P'(H2O) With waxing. In addition, P'(O2) and P'(CO2), decreased similarly and more gradually with increasing coating deposits in 'Bosc' than in the other cultivars. The epidermis of 'Bosc', comprising an irregular layer of lignified cells, seemed to have high P'(H2O) and low P'(O2) and P'(CO2). Improving the coating deposit on the skin blocked the lenticels, providing a more variable reduction in P-CO2 than in P'(O2). However, this did not effectively cover the lignified cells in the epidermis, providing variable and small changes in P'(H2O). These results show that optimisation of surface coatings for pears must take into account differences in the nature of the skin. (C) 2001 Elsevier Science B.V. All rights reserved.