Comparison between fixed and flexible chamber methods for measuring respiratory rate under steady and unsteady states

A proposed new method is effective for measuring the respiration rates of fruits and vegetables not only under stable temperature or gas component but under a dynamically changing environment, such as during cultivation in an open field or during transit after harvest. The gaseous components within a flexible plastic film bag, in which the horticultural product or its parts is enclosed, are measured continuously or periodically. The method is called the flexible chamber method for measuring respiration rates. By using fresh air or some component gas initially, and adjusting the ratio of the air volume and that of the reaction product, this method can control the internal gas concentration of the chamber and the turnover rates. In this research, cucumber was used. A decrease in oxygen concentration from 21 to 8% repressed the respiration rate while increasing the carbon dioxide concentration from the ambient 0.03 to 6%. This respiration repression was caused by the high CO2 and low O2 concentrations rather than by the interaction between the two gases. At 8% oxygen (Fig. 5), the oxygen consumption rate decreased more slowly than did the carbon dioxide emission rate so that the final carbon dioxide concentration approached 5%. Hence, the respiratory quotient (RQ) increased from 1.0 to about 1.5. The oxygen concentrations seem to border the anaerobic respiration phase. When the pressure in the chamber was increased from the ambient atmospheric pressure, the respiration rate tended to be repressed temporarily which indicates fluctuating pressure may influences the respiration process. The new proposed method of measuring the respiration rate is adaptable to a diverse environment as mentioned above, especially when the atmospheric pressure is under an unsteady state.