Efficient estimation of gas exchange and respiration kinetics in apple using pathlength-resolved GASMAS

Optimization of controlled atmosphere (CA) storage of pome fruit crucially depends on understanding of respiratory gas exchange. Different fruit properties are involved in describing gas transfer and respiration kinetics, which can vary between cultivars, fruit batches and individual fruit. Determination of these properties currently requires a combination of different time-consuming techniques and data analysis procedures. This study introduces a more efficient single method for O2 gas exchange characterization of fruit based on the non-destructive pathlength-resolved GASMAS (gas in scattering media absorption spectroscopy) technique. GASMAS was used to measure the absolute intercellular O2 concentration in fruit of different apple cultivars (Malus x domestica Borkh.) with distinct porosity including 'Jonagold', 'Braeburn', and 'Nicoter'. To resolve the ambiguity between variation in pathlength and O2 concentration inherent to GASMAS, the pathlength travelled through pores cavities was quantified through a second GASMAS measurement at the absorption line of H2O vapour. Dynamic experiments were then performed in which the fruit was subjected to varying external O2 concentrations while measuring the internal O2 response. The observed dynamic profiles of external and internal O2 concentration were fitted with a lumped -respiration model to estimate the effective mass transfer coefficient, maximum respiration rate and Michaelis Menten constant of intact fruit. The model showed a good fit (R2>0.95) with the measured data and reliable estimates for the model parameters. The proposed method provides a novel and more efficient way to estimate the gas exchange properties of fruit that are essential for optimizing CA storage conditions. Future challenges for the proposed method are with applications to other gasses such as CO2 and ethylene.