Effect of storage conditions on phenolic compounds of raisins produced without and with pre-treatment of grapes with extra virgin olive oil

Abstract

The study evaluated the influence of process and storage conditions (180 days at 4, 25, and 35 °C) on the phenolic compounds (PC) profile of BRS Vitoria grapes dehydrated with and without an alternative pre-treatment with extra-virgin olive oil using HPLC-DAD-ESI-MSn. The process degraded PC, particularly anthocyanins and flavonols. Pre-treatment significantly improved the retention of anthocyanins (0.69–183 mg malvidin-3-glucoside⋅kg−1), with retention 1.9–2.9 times higher than control during storage at 4 and 25 °C. For flavonols, pre-treatment did not affect the total content (35.4–64.9 mg quercetin-3-glc⋅kg−1), with temperature being the primary influence. At 35 °C, all the flavonols and most anthocyanins degraded. Notably, diglycosylated and diglycosylated coumarilated derivatives of malvidin remained until the end of the storage, showing the compound structure's influence on stability. Storage at 4 °C was beneficial and may be a better temperature for maintaining these compounds. Hydroxycinnamic acid derivatives, non-extractable PC, were less affected by processing and storage (143–270 mg caftaric acid⋅kg−1), likely due to matrix release under acidic conditions, especially at higher temperatures. These findings highlight the complexity of maintaining phenolics during processing and shelf life, influenced by factors like pre-treatment, drying time, grape's initial phenolic content, compound structure, and matrix effects.