Temperature and light conditions affect stability of phenolic compounds of stored grape cane extracts

This study aimed to determine the stability of PCs in grape canes extracts stored at different temperatures and light conditions. The PCs composition was monitored every-two weeks during three months by liquid chromatography coupled to diode array and fluorescence detectors (LC-DAD-FLD). Initially, stilbenes represented 87 % of total PCs. Storage at -20 and 5 °C reduced PCs 8 and 6 %, respectively. When extracts were exposed to 25 and 40 °C, the degradation of (+)-catechin and (-)-epicatechin was faster than under lower temperatures, and light accelerated the degradation kinetics. trans-piceatannol showed particularly sensitive to temperature increase, being mostly degraded after two weeks stored at 40 °C. Conversely, degradation of trans-resveratrol and ε-viniferin was mostly catalyzed by light, since nearly 70 % of them were degraded at 40 °C under light, in comparison with a 23 % reduction of trans-resveratrol and no changes of ε-viniferin at 40 °C in darkness.