Apparent respiratory quotient observed in headspace of static respirometers underestimates cellular respiratory quotient of pear fruit

Abstract

A three-compartment non-equilibrium gas transport model of 'Conference' pear fruit under controlled atmosphere (CA) storage was developed. The model fruit tissue consists of cells, in which the concentrations of respiratory gasses can show gradients, and intercellular space, in which gasses are uniformly distributed. Non-equilibrium of gas concentrations in the cell compartment and intercellular space is assumed. A respiration model based on Michaelis-Menten respiration kinetics without inhibition of respiration by CO2 and incorporating down-regulation of the maximal O2 consumption rate in response to O2 was developed. Conversion of CO2 dissolved in the cell compartment to hydrogen carbonate at a constant pH of 5.0 was included. The model was validated based on experimental data of 'Conference' pear fruit during a complete depletion experiment starting from 3.58 mol m -3 O2 and 0.00 mol m -3 CO2. Model predictions match experimental observations well. Gas concentrations in the cell compartment were found to be in 2 equilibrium with the gas concentrations in the intercellular space. The model was used to calculate apparent respiration rates and RQ as if measured in the storage headspace. Apparent values were compared to actual values in the fruit cells and it was found that apparent respiration rates and RQ, calculated based on headspace measurements, underestimated the actual respiration rate and respiratory quotient in the fruit cells. Relative differences of 4 %, 41 % and 41 % were found for the apparent O2 consumption rate, CO2 production rate and RQ, respectively. This affects the design of commercial RQ based DCA systems.

Multiscale modeling of RQ-DCA storage of different pear cultivars using a hybrid physics-based stochastic approach

“…As expected from earlier research (Bessemans et al, 2020;Delele et al, 2019), the RQ measured in the air underestimates the actual RQ value inside the pears. It is noted that this difference depends on the duration of the RQ-measurement.…”

“…A one-phase model (Eq. 2.1) was used instead of the more complex two-phase model where an equation is defined for each phase (cells and pores) individually, as Bessemans et al (2020) already showed the existence of equilibrium between the cells and pores during RQ-DCA storage conditions.…”

“…Since the development of RQ-DCA, a few numerical studies have been performed to analyze the RQ response of pears during RQ-DCA storage. Bessemans et al (2020) revealed a difference between the RQ value in the pear cells and the RQ value in the headspace of a jar filled with an intact pear using a lumped gas transport model. The RQ distribution in a small container with three boxes filled with pear fruit has been studied for three different O2 conditions, indicating a homogeneous RQ distribution in the free airspace (Delele et al, 2019).…”

SafePod: A respiration chamber to characterise apple fruit response to storage atmospheres

“…The rapid RQ profile presented in this paper is typically a U shaped curve. The initial decrease in RQ as O2 decreases is considered to be an artefact arising from solubilisation of O2 and CO2 in apple tissues as described and modelled by Bessemans et al (2020) with RQ being underestimated due to the higher solubility of CO2 compared to O2. Comparison of the rapid RQ profile with the slow RQ profile, during which fruit can acclimatise, (Fig.…”

“…An RQ less than 1.0 occurs when lipids are used as a substrate (Cameron et al, 1994). However, Bessemans et al (2020) have produced a model to demonstrate how gradients in gas concentrations between fruit flesh and chamber headspace affect the measurement of respiration rates and the RQ. Given the high solubility of CO2 there is a tendency to underestimate RQ.…”