Non-destructive 1H-MRI assessment of flesh bruising in avocado (Persea americana M.) cv. Hass

Abstract

Bruising of the mesocarp in avocado fruit is an important postharvest issue for the industry. Proton magnetic resonance imaging (1H-MRI) was used as a non-destructive tool to monitor bruise expression over time in avocado cv. Hass fruit. 1H-MRI clearly identified fruit morphological features and bruised mesocarp tissue. The pixel intensity value of T2 weighted spin echo 1H-MRI images of avocado fruit pericarp changed over time with fruit softening. Bruised mesocarp tissue in impacted fruit appeared relatively hyperintense (brighter) in T2 weighted 1H-MRI images. For firm ripe fruit impacted from 25cm drop height (0.38J±0.004) and for firm ripe fruit impacted from 50cm drop height (0.81J±0.011), hyperintensity in the mesocarp beneath the impact point was evident immediately after impact. However, visible symptoms of bruising in the form of flesh browning did not appear in parallel serial destructive assessments until after day 1 following impact on day 0. The brown, bruised mesocarp volume in ripe fruit increased progressively over the assessment period of 3 days. This trend was evident in destructive assessments as well as in 1H-MRI images. In hard green mature fruit impacted from 100cm drop height (1.68J±0.020), contrast between mesocarp tissue beneath the impact site and surrounding sound mesocarp was evident in T2 weighted 1H-MRI images from day 0. However, no bruise symptoms were evident as flesh browning upon serial destructive assessments of fruit over the 3 days assessment period. The average pixel intensity values at the impact site in T2 weighted 1H-MRI images for both firm ripe and hard green mature fruit decreased over the period of assessment. In contrast, the pixel intensities in the T2 weighted 1H-MRI images of diseased flesh increased over time.