Estimation of ‘Hass’ Avocado (Persea americana Mill.) Ripeness by Fluorescence Fingerprint Measurement

Abstract

Avocados (Persea americana Mill.) are a climacteric fruit which ripen until after harvesting, and their ripeness is an important quality attribute that determines consumer liking. In this study, the ripening degree of ‘Hass’ avocados was evaluated non-destructively by measuring the skin and flesh using the fluorescence fingerprint (FF). FF, also known as the excitation-emission matrix (EEM), is a set of fluorescence spectra obtained at consecutive excitation wavelengths. It was found that as ripening progressed, the fluorescence signal of chlorophyll A in the skin and flesh decreased significantly as the hardness of the avocado flesh decreased. The hardness value was estimated from the FFs of the skin and flesh using partial least-squares regression, and minimum prediction errors of 2.02 N cm−2 and 2.05 N cm−2 were obtained for the prediction models using FFs of the flesh and skin, respectively. Furthermore, ripeness levels (unripe, ripe, and overripe) were discriminated non-destructively from the FFs of the skin with an accuracy of 90% for the validation dataset. The measurement and analysis technique demonstrated in this study is rapid and accurate, and can contribute to supplying uniform agricultural products to consumers.