Evaluation of avocado fruit maturity with a portable near-infrared spectrometer

• Three season calibration of portable NIR spectrometer for avocado maturity.
• Commercial validation over two further seasons for three cultivars.
• Fruit peel removed before scanning to improve accuracy.
• Robust calibration model is comparable to conventional methods.
• Analysis time per fruit is less than 30 s per fruit.

There is considerable financial incentive for avocado (Persea americana Mill.) growers in South Africa to begin harvest as soon as the minimum fruit maturity has been reached. The need to quickly process a large amount of samples for maturity determination pre- and postharvest using a user-friendly instrument provided motivation this study. ‘Fuerte’, ‘Hass’ and ‘Carmen®-Hass’ fruit were included in the calibration of the portable near-infrared spectrometer. The calibration included fruit from three seasons and the external validation included fruit from two further seasons. With this portable NIR spectrometer, it was not possible to develop a calibration model to accurately measure the maturity of avocado fruit non-destructively (‘Fuerte’: R2 = 0.654, RMSECV = 2.62, RPDCV = 1.23, ‘Hass’ and ‘Carmen®-Hass’: R2 = 0.400, RMSECV = 2.94, RPDCV = 0.79). A model incorporating all three cultivars, with the fruit peel removed, provided comparable results to the commercial method when using at least four fruit per sample (R2 = 0.732, RMSEP = 1.83, RPD = 1.14). The measurement of a single fruit took 30s, and could be conducted pre- or postharvest.