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

• Published in: Postharvest biology and technology 2020-04, Vol.162, p.111104, Article 111104
• Main Authors: Bessemans, N., Verboven, P., Verlinden, B.E., Janssens, M., Hertog, M.L.A.T.M., Nicolaï, B.M.
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Depletion; Dynamic controlled atmosphere; Equilibrium; Fruits; Gas transport; Headspace; Mathematical model; Non-equilibrium; Oxygen consumption; Pyrus communis L; Quotients; Respiration; Respiration rate; Respiratory quotient; Respirometers; Storage
• ISSN: 0925-5214; 1873-2356
• DOI: 10.1016/j.postharvbio.2019.111104

•A lumped three-compartment gas exchange model of pear fruit under CA was developed.•In-cell O2 and CO2 concentrations are in equilibrium with pore space concentrations.•RQ observed in storage headspace underestimates cellular RQ. 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 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.