Determine whether ethylene respiration rate is indicative of fruit ripeness in green bananas.
The CI-900 ethylene meter was used to evaluate ungassed mature green bananas donated by Organically Grown in Gresham, Oregon, USA. The CI-900 is able to detect ethylene during the pre-climacteric stage. From the measurements given by the CI-900, ethylene production rates were calculated for the individual bananas. A starch test was also used to gauge the ripeness of the bananas. The results of the starch test and calculated productions rates were in good agreement with published literature.
Procedure for CI-900 and Gas Chromatograph:
Figure 1: Diagram of experiment setup for in-lab measurements with the CI-900.
CI-900 notes: Software Version 12.03 was used, and required the following configuration:
1) Manual initial loop
2) Conditioning Chamber B set to active, filled with distilled water, and run in “clean” mode until the background signal is below 20ppb.
Procedure for Starch test:
CI-900 Test Results
|CI-900 (ppm C2H4)||GC||Production Rate
|Green Banana 1||0.047||undetectable||3.02|
|Green Banana 2||0.054||undetectable||4.08|
|Green Banana 8||0.057||undetectable||4.71|
|Yellow Banana 14||0.079||undetectable||9.04|
|Yellow Banana 16||0.084||undetectable||10.37|
Table 1: CI-900 and GC values represent a single measurement of the fruit chamber headspace after 3 minutes. The production rate was calculated from the CI-900 measurement. All measurements occurred at ambient temperature, ~ 25°C.
|Temperature||13°C (56°F)||15°C (59°F)||18°C (65°F)||20°C (68°F)|
Table 2: Rates of ethylene production, low end for mature-green bananas and high end for ripening bananas .
The calculated ethylene production rates shown in table 1 are in agreement with the published production rates shown in table 2. The green mature bananas lay just below the midpoint of the 20°C range. Whereas, the yellow bananas towards the high end. The green bananas ripened within a week while stored at ambient conditions in the lab. It should be noted all measurements were carried out at ~25°C. The increase in temperature could account for the slightly higher ethylene production then reported in literature.
Starch Test Results
Figure 2: Starch Stain of Green Mature Banana #8.
Figure 3. Starch Stain of Yellow Mature Banana #16.
Figure 4. Banana Starch Index Chart .
As it can be difficult to determine fruit ripeness and maturity based solely on outer appearance, starch tests were conducted to validate the maturity of one yellow and one green replicant. Comparing figures 2 and 3 to the published banana starch index chart shown in figure 4, indicates that the green bananas, represented by banana 8, were in stage 2 of the ripening process with a high level of starch content and a slight yellowing of the skin. Whereas the yellow banana, represented by banana 16, was in stage 7 with little starch content and spotting of the skin.
The starch test indicates that the green bananas should have an ethylene production rate in the lower half of the published range, and that the yellow bananas should have an ethylene production rate near the maximum. The green bananas had an average production rate of 3.94 ul C2H4/kg·hr (s=0.85 ul C2H4/kg·hr) during stage 2 of the ripening process. The yellow bananas had an average production rate of 9.75 ul C2H4/kg·hr ( s=0.94 ul C2H4/kg·hr) during stage 7 of the ripening process. These results suggest that ethylene production rate increases as the bananas ripen.
With further testing and more data points gathered, ethylene production rate (measured by the CI-900) could be used to indicate ripeness of bananas. We would like to see these preliminary results validated by researchers with access to freshly harvested or intact green bananas.
A. Kader. Banana: Recommendations for Maintaining Postharvest Quality. UC DAVIS DEPARTMENT OF PLANT SCIENCES. http://postharvest.ucdavis.edu/PFfruits/Banana/
Fruit Ripening. UC DAVIS POSTHARVEST TECHNOLOGY. POSTHARVEST HORTICULTURE SERIES No 9. 2010. pg 51