Determination of the low oxygen limit for several commercial apple cultivars by respiratory quotient breakpoint

Abstract

Abstract Low oxygen limits for apple ( Malus domestica , Borkh) fruit were determined using modified-atmosphere packaging (MAP) techniques. Fruits were sealed in low density polyethylene (LDPE) packages and placed at 0°C until steady-state respiration was reached. Steady state O 2 and CO 2 partial pressures were varied by altering package thickness, package surface area, and the total fruit weight within the package. Based on measured permeabilities of the LDPE packages to O 2 and CO 2 , package partial pressures were used to determine the gas flux for O 2 and CO 2 for each package, with gas flux rates representing respiratory rates. The effect of O 2 partial pressure on O 2 uptake, CO 2 production, and the respiratory quotient (RQ) was then determined. As the O 2 partial pressure decreased to approximately 2 kPa, RQ remained relatively constant. A marked increase in the RQ (the RQ breakpoint) occurred below 2 kPa O 2 , which was associated with elevated ethanol concentrations. The low O 2 tolerance limit was then estimated for each cultivar as the O 2 level at the RQ breakpoint; these values ranged from 0.7 kPa O 2 for cultivars “Red Delicious” and 0.8 kPa for “Law Rome” to approximately 1.9 kPa for “McIntosh”.