Model based leak correction of real-time RQ measurement for dynamic controlled atmosphere storage

A method was developed to correct real-time measurements of the respiratory quotient (RQ) of pome fruit for gas leakage of a cool room. The method is based on a general leakage model that was simplified by performing sensitivity analysis of the contribution of the pressure driven and concentration driven gas transport terms. The analysis showed that pressure driven leakage was dominant over diffusive leakage. The methodology was validated successfully using an empty storage container at 0.4 kPa O2 and 1.3 kPa CO2. A sensitivity analysis using virtual storage experiments showed that the error of the RQ estimates with leak correction was 0%, while without leak correction they increased to above 700%. Finally, the validated model was successfully implemented in an automated RQ-DCA control system using 'Braeburn' apple fruit (Malus × domestica 'Braeburn' 2x). RQ estimates without leakage correction were heavily biased when leakage of atmospheric air into the storage container occurred and would lead to erroneous control of the storage atmosphere composition. With the developed leakage correction, RQ measurements were found to be accurate during decreasing as well as increasing atmospheric air pressure.