When should postharvest avocado fruit rots be inspected via X-rays? Relationship between internal fruit rot development and skin color alteration in “Hass” avocados

Abstract

Internal fruit rot during postharvest ripening poses a significant challenge to maintaining avocado quality. In the present study, we focused on the changes in the skin color of ‘Hass’ avocados during ripening as an indicator of the timing of avocado rotting. The timing of inspection by X-ray imaging is crucial for detecting internal fruit rot, because the causal fungi remain quiescent in unripe fruit. In other words, if avocados are inspected too early using X-ray imaging, potentially rotten fruit may be mistakenly labeled as healthy. In this study, the development of fruit internal rots in 422 ‘Hass’ avocados during five days of ripening was non-destructively observed using X-ray images in three experiments. The relationship between fruit rot severity; changes in skin color metrics, i.e., the values of lightness (L*), chroma (C*), hue angle (h°) from the CIE L*a*b* color system, were analyzed. Internal fruit rot was observed when skin color fell within a specific range despite initial skin color variations within and across experiments. Furthermore, X-ray images showed that 91 %, 70 %, 48 %, and 10 % of potentially rotten fruit on day 4 did not show internal rot symptoms on days 0, 1, 2, and 3 in the storage period, respectively. These results imply that testing fruit before the skin color reaches specific levels would lead to a significant increase in false negatives. Finally, we provided a color bar illustrating the skin color stages after which postharvest inspection should be performed to visually highlight the appropriate inspection timing. This study underscores the importance of the inspection timing of avocados and demonstrates the potential of skin color metrics as objective criteria for determining the timing of inspection.