Respiratory rate and quality changes in fresh-cut pears as affected by superatmospheric oxygen

Changes in the respiration rate of fresh-cut "Flor de Invierno" pears stored under superatmospheric oxygen concentrations were studied and compared to those observed under traditional modified atmosphere packaging conditions. Changes in package headspace O-2 and CO2 concentrations throughout storage were curve-fitted to non-linear equations, calculating respiration rates by combining the derivatives of the equations and the gas permeations throughout storage. Moreover, relationships between respiratory activity and quality parameters of fresh-cut Flor de Invierno pears dipped into an antioxidant solution (0.75% N-acetylcysteine and 0.75% glutathione) were assessed. CO2 production of fresh-cut Flor de Invierno pears stored under 70 kPa O-2 atmospheres was successfully estimated with the proposed mathematical procedure. This method also proved to describe well CO2 production rates of fresh-cut pears stored under initial 2.5 kPa O-2 + 7 kPa CO2 or 21 kPa O-2. In addition, a modification of Michaelis-Menten enzyme kinetics was adequate to describe the changes in estimated CO2 production due to fermentative processes occuring under low oxygen concentrations. Superatmospheric O-2 concentrations seem to promote oxidative processes, which result into a dramatical modification of some quality attributes of fresh-cut pears.