Kinetic Model for Colour Changes in Bananas During the Appearance of Chilling Injury Symptoms

The impact of chilling injury (CI) on the colour of bananas at different ripening stages was investigated. Bananas were stored at 6 and 13 A degrees C for 2 days to induce CI symptoms. Images of the bananas were acquired in 1-h time intervals during the subsequent appearance of CI at room temperature using RGB imaging system to monitor the colour changes. The raw RGB values obtained were transformed to normalized rgb and CIEL*a*b* space to remove the brightness from the colour and to distinguish the colour similar to human perception. The total colour difference (a dagger E) was calculated from CIEL*a*b* space to evaluate the overall colour difference of the samples. Hue (H) values were obtained after transformation into HSI space, since it provides reasonable data on the chlorophyll content as it was shown in many studies on fresh fruit. Visual assessment was carried out to grade the degree of injury and to correlate with colour parameters. Spectroscopy in the visible wavelength range, in diffuse reflectance geometry was applied to assess colour changes caused by variation in the fruit chlorophyll content. Results indicate significant (P < 0.0001) influence of temperature, ripening stage and post-chilling time on colour parameters. Strong correlations (R (2) > 0.9) were found between r, g and H colour parameters and visual assessment. The values of r increased while the g and H decreased. The kinetic of r, g and H development after chilling treatment fitted well to the first-order kinetic model. Based on the kinetic rate constant, banana at ripening stage 5 showed enhanced susceptibility to chilling injury when compared to banana at ripening stage 4. Spectral reflectance revealed that diminishing chlorophyll content as well as tissue browning and changes in the carotenoids need to be considered when monitoring the CI symptoms. Application of principal components analysis providing clear separation of control and stressed samples capturing variances of 80.91% and 7.24% (r), 82.96% and 7.52% (g), 91.57% and 3.15% (b) and 79.83% and 7.91% (H) for components PC1 and PC2, respectively.