Comparison of unsteady- and steady-state methods for produce respiration rate determination

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Equations were developed to predict the behavior of the measured respiration quotient (RQ measured ) during the measurement of produce respiration rates using various unsteady- and steady-state systems. These models predicted that the RQ measured determined in unsteady-state closed chambers would be a strong function of system loading and the produce’s internal pH whereas measurements in open steady-state systems would be independent of these variables. An examination of our previously published results with rutabaga ( Brassica napobrassica ) as well as other unsteady- and steady-state literature data obtained from various other produce verified the trends predicted by the models. The transient build-up of CO 2 species inside the produce under unsteady-state conditions, and the resulting metabolic changes that occur to compensate, can lead to large swings in RQ measured . In contrast, inside modified atmosphere packages (MAPs), when the produce is allowed to gradually reach steady-state conditions, RQ measured values remain relatively constant. It would appear that vegetables with a relatively high internal pH (e.g., lettuce or celery) are more sensitive to the presence of elevated levels of CO 2 whereas vegetables with lower internal pH (e.g., broccoli or spinach) or most of the fruits are less affected.