Non-invasive detection of surface features of three plum types

Plums are covered by a layer of epicuticular wax. The purpose of this study was to examine the effect of different surface treatments on the light reflection of three plum types, identify the major drivers of glossiness (luster) changes in time and explain their variation using statistical analysis. Three surface conditions (natural surface, chemically-treated, manually polished) combined with three plum types (blue European plums, yellow mirabelle and greengage) were examined. Light reflection over time was measured with a luster sensor type CH-72H resulting in 860 measurements. The surface treatment affected light reflection and thus luster levels; removal of the wax bloom increased both glossiness and luster level. Statistical analysis has shown that the plum type (blue European plum, mirabelle, and greengage) had negligible influence on the results, whereas 60% of the statistical variation of luster levels was caused by ageing and storage. A model was developed as a first step, opening further possibilities in determining and possibly predicting the freshness of plums.