Determining banana maturity with the CI-900

Objective:
Determine whether ethylene respiration rate is indicative of fruit ripeness in green bananas.

Method:
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:

1. Load the sample specimen into the fruit chamber
2. Measure the fruit headspace with the CI-900
3. After sampling the headspace for exactly 3 minutes, trigger a manual initial loop.
4. Take a syringe sample and run in the GC. Record result in Excel. Note: Sample should be taken as soon as possible to the start of the initial loop.
5. Vent fruit chamber, evaluate data collected by CI-900

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:

1. Mix 1 part I₂ to 2 parts KI in 50ml distilled water.
2. Cut the banana into several cross and one longitudinal section.
3. Dip each slice into the mixture for 20 seconds.
4. Rinse the slices with tap water and allow to air dry on a paper towel.
5. Document the test.

CI-900 Test Results

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.

Table 2: Rates of ethylene production, low end for mature-green bananas and high end for ripening bananas [1].

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 [2].

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.