pH and Thermal Stability of Anthocyanin-based Optimised Extracts of Romanian Red Onion Cultivars

Total phenolics and anthocyanins in ten samples of Romanian red onion cultivars, extraction optimisation and pH/thermal stability were investigated. Extraction with 80% aqueous ethanol leads to an increased anthocyanin yield. The level of phenolics and anthocyanins in bulbs is highly variable and was found higher in the Red of Turda cultivar. The highest value of 99.66 mg/100 g FM was obtained for red onion dry skins. Strong acidic conditions favoured the better stability of anthocyanin extracts during 10-day storage. The first order rate constant value of anthocyanin degradation during storage calculated at different pH increased almost 17 times when pH increased from 1.0 to 9.0. Results of thermal analysis performed by differential scanning calorimetry showed that temperatures over 45 degrees C already induced anthocyanin degradation in extracts. These results may become useful for establishing the appropriate conditions of processing and storage of anthocyanin-based foods. The obtained data on total phenolics and anthocyanins in Allium cepa L. may become relevant for future estimation studies of their daily consumption and for completing the national food composition databases.