Dynamic controlled atmosphere: Does the frequency of respiratory quotient determination during storage affect apple fruit metabolism and quality?

This study aimed to determine the effects of the frequency of respiratory quotient (RQ) determination during storage in a dynamic controlled atmosphere (DCA-RQ) on the anaerobic metabolism and quality of 'Galaxy' apples during two seasons. Another aim was to identify a relationship between the RQ determination frequency and the RQ level adopted in the metabolism and quality of apples after long-term storage. Fruit were harvested at the commercial harvest peak and stored for nine months under controlled atmosphere (CA) and DCA-RQ 1.3 and 1.5 conditions, with four frequencies of RQ determination: once a week, twice a week, daily, and without RQ determination. Storage under DCA-RQ and the RQ determination frequency affected fruit metabolism and quality. Daily RQ determination induced ethylene production under DCA-RQ 1.5 due to frequent low oxygen stress. The daily RQ determination also induced higher anaerobic metabolism, flesh breakdown, and decay incidence, making a daily RQ determination in both RQ levels tested not recommended. Fruit quality was better maintained when the RQ determination frequency was once and twice a week for DCA-RQ 1.3 and twice a week for DCA-RQ 1.5, resulting in higher quantities of healthy fruit and higher flesh firmness maintenance without inducing excessive anaerobic metabolism compounds production. The RQ determination frequency has more influence on anaerobic metabolism induction than lowering the oxygen from 1.2 kPa (CA) to 0.15 kPa (DCA-RQ 1.5), which evidences that there are two main ways to manage anaerobic metabolism induction in 'Galaxy' apples: changing the RQ level adopted and changing the RQ determination frequency. Without the stress caused by RQ determination, storage under DCA-RQ conditions does not result in quality maintenance compared to fruit submitted to RQ determination.