Non-invasive determination of the quality of pomegranate fruit

Abstract

In the apparent absence of non-invasive studies of the glossiness and roughness of pomegranate fruit (cv. ‘Hicaz’) during storage, we investigated changes in their surface micro-structure using two new non-destructive technologies: a profilometer providing 3D digital photography and surface roughness as visual and parametric roughness (Ra; Rz) as well as glossiness by non-invasive luster sensor technology. The 3D intact sections of the pomegranate showed a shimmering surface with fresh fruit, but a rough structure in the RGB images after three weeks storage, associated with a wider range of values, i.e. higher peaks and lower troughs over time, which was visualised in the images.The roughness coefficients Ra and Rz, provided by the 3D-profilometer, confirmed the colour-coded visualization in the false images and increased with storage time: The roughness values (Ra) were 11μm for the fresh pomegranate fruit with a smooth peel; 24μm with aged pomegranate and 43μm with the old shriveled fruit. The Rz values were 69μm for the fresh pomegranate fruit with the smooth surface, 148μm at the intermediate pomegranate and 255μm for old fruit.During the three weeks storage, the luster values of red or yellow, non-russet peel sections decreased more rapidly from 90 to 50 arbitrary units (a.u.) than those of the russet peel; the latter areas with a rough appearance showed significantly lower luster values of ca. 40a.u. compared with the russet-devoid areas. Luster and roughness values were always inversely correlated and confirmed their visual appearance. The lack of significant differences between the luster values of the red and yellow peel portions supports our hypothesis that colour plays an insignificant role in this luster/gloss detection, and proves the suitability of this innovative real-time, contactless and cost-effective sensor technology as a novel evaluation used in post-harvest technology.