Chemical and thermodynamic analyses of the surface waxes of ‘Korla’ pears: Relationships between the surface waxes and skin greasiness

Abstract

The surface waxes of ‘Korla’ pears can become greasy during storage when overripened, and the wax changes are considered to be responsible for this disorder, but the relationship between the wax changes and skin greasiness of ‘Korla’ pears remains unclear. We profiled the chemical and thermal changes in the surface waxes of ‘Korla’ pears as skin greasiness increased when stored at 25 °C. We also recorded the effects of treatment with 1-methylcyclopropene (1-MCP), which is known to interfere with this aetiology. The results show that as skin greasiness increased, there were steady increases in the more fluid wax compounds, mainly of the n-9 olefins (C17, C19, C21, C23 and C25). These fluid olefins were detected only in greasy fruit, and their amounts were highly correlated with greasiness. Separation experiments further confirmed that the accumulation of fluid olefins increased the fluidity of the solid alkanes of the ‘Korla’ pear waxes. The thermodynamic analyses show that melting temperatures and enthalpy both decreased with increases in wax fluidity. Moreover, the chemical and thermal changes in these waxes, along with greasiness can be suppressed by 1-MCP. These results indicate that the accumulation of fluid n-9 olefins raises wax fluidity, while the thermal analyses indicate that this effect could be similar in mechanism to those of the plasticizers used in the manufacture of synthetic polymers.