Effect of the transport vibration on the generation of the color reversion in blackberry fruit

Abstract

Mexico provides 95% of the export market blackberry (Rubus fruticosus) worldwide. The characteristic black color of this fruit is an important quality factor. During its postharvest management, it can reverse its color from black to red (color reversion) this being a rejection factor in the market. Within 3-5% of the exported fruit can be rejected due to this problem. The origin of this change is not determined yet but can involve varietal aspects and postharvest handling. The objective of this study was to determine the effect of transport vibration on the color reversion. To identify the vibration conditions that generate the damage, exporting boxes with 12 clamshells of 6 oz with blackberry 'Tupy' were put under vibration patterns (5-30 Hz) with amplitude of 0.5 g. Under the identified damage conditions, different blackberry boxes were put at those conditions of vibration for 10 and 30 min, respectively, and later the fruit was stored at 3°C and 95% of HR for 2 days. The incidence of damage was evaluated and the black and red drupelets were separated from each fruit, frozen at -70°C and freeze dried for quantification of monomeric and polymeric anthocyanin. Fresh samples of each condition were prepared for its observation by optic microscopy and transmission electron microscopy (TEM). The frequency of 10 Hz and 0.5 g of amplitude generated color reversion, internal cellular damage and possible molecular changes in the anthocyanins structure. The monomeric anthocyanin content was lower on reverted drupelets (4.535 mg cyanidin-3-O-glucoside g-1 lyophilized sample) with respect to non-reverted (7.746 mg cyanidin-3-O-glucoside g-1 lyophilized sample), likewise the index of percentage of polymeric color was lower on the black drupelet (23%) in comparison with the red drupelets (37%). The tissue of the non-reverted drupelets showed a higher integrity and cellular order in comparison with the tissue of the drupelets with reversion of color. These results indicate that the frequency of 10 Hz should be avoided during the transportation of these fruits.