Can visual reflectance indices be related to ripeness of banana fruit?

Bananas (Musa sp. [AAA group, Cavendish subgroup] 'Williams') grown under paper bunch covers appear riper, being a lighter shade of green at maturity, than fruit grown under plastic bunch covers. However, such fruit ripen more slowly than fruit under plastic, in terms of respiration rate and ethylene release, based on measurements of individual fingers enclosed in containers at 20°C and ventilated with humidified air containing 300 μl.L-1 propylene for 36 h. There was no significant difference in soluble solids concentrations between the two lines of fruit after seven days of ripening. The objective of this study was to determine whether reflectance spectra can be correlated with physiological ripeness to monitor ripening of bananas non-destructively. Colorimetric readings showed that the initial visible differences in skin colour between the lines largely disappeared by day 5 of ripening. A number of pigment indices were calculated using these spectra, targeting chlorophyll, carotenoids and xanthophylls. Some of these measures were clearly lower in pale bananas grown under paper bunch covers but converged after day 5 of ripening. The most promising measurement for assessing ripeness stage was the chlorophyll index (calculated from the second derivative of absorbance spectra as A<inf>800</inf>/A<inf>700</inf>-1), with a consistent value at harvest, despite growth condition, and increase with fruit ripening.