Non-destructive detection of the wax bloom on European plum during post-harvest handling

Abstract

Post-harvest handling may disturb the wax bloom of plum, blueberry or grape berry, which constitutes both an external visual (speckled fruit) as well as physiological fruit quality parameter (disturbing the water loss barrier) with the following results:(a)Destructive ESEM analysis showed the wax bloom of European plum to be caused by wax platelets, where the wax is largely re-distributed on handling rather than removed.(b)CIE L* values significantly (p<0.05) decreased from 37.3 to 28.1, indicating a darker plum surface after polishing. The a-value of the plum surfaces increased significantly from 2.35 to 2.86, whereas b-values decreased ca. 2.5-fold from −13.9 to −5.0 after polishing viz the plum surface became more red and less blue.(c)Luster levels (glossiness) detected non-destructively increased by almost 3-fold from 111 (SD+20) to 284 (SD+32) relative units.(d)Analysis of RGB images visualised the relative wax distribution over the fruit surface after polishing, as uneven with a more dense wax coverage at the fruit apex and less at the fruit equator, where the contacts by hand are most frequent.The changes in L and b values, and to a lesser extent in the a-value, luster levels and RGB image analysis may be used as a technical fruit quality parameter as determined non-destructively.