Comparison of unsteady- and steady-state methods for produce respiration rate determination
Robert W. Lencki
Postharvest Biology and Technology Volume 31, Issue 3 , March 2004, Pages 239-250
2004
บทคัดย่อ
Equations were developed to predict the behavior of the measured respiration quotient (RQmeasured) during the measurement of produce respiration rates using various unsteady- and steady-state systems. These models predicted that the RQmeasured 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 CO2 species inside the produce under unsteady-state conditions, and the resulting metabolic changes that occur to compensate, can lead to large swings in RQmeasured. In contrast, inside modified atmospherepackages (MAPs), when the produce is allowed to gradually reach steady-state conditions, RQmeasured 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 CO2 whereas vegetables with lower internal pH (e.g., broccoli or spinach) or most of thefruitsare less affected.