Process and storage stability of anthocyanins and non-anthocyanin phenolics in pectin and gelatin gels enriched with grape pomace extracts

Gelatin and pectin gels were supplemented with anthocyanin extracts obtained from grape pomace and stored either under neon light (20 ± 2 °C) or in the dark (20 ± 2 and 6 ± 2 °C, respectively) for a period of up to 24 weeks. During storage, antioxidant activities of the samples (FRAP and TEAC assays), total phenolic contents (Folin–Ciocalteu assay) and the amounts of monomeric and polymeric anthocyanins and of non-anthocyanin phenolics were monitored spectrophotometrically and by HPLC, respectively. Processing of the gels had the most significant effect on the total phenolic contents in all samples, resulting in total losses up to 24.6%. Light considerably decreased the phenolic compounds during storage, whereas the effect of temperature on their stability was less pronounced. Total phenolic contents of illuminated samples decreased from 243.6 to 82.6 mg/kg in the gelatin gels within 24 weeks of storage and from 279.8 to 139.5 mg/kg (pectin gel, 16 weeks of storage). In contrast, antioxidant activity of the samples was only slightly reduced or remained virtually unchanged. Thus, the model gels still exhibited brilliant colors and strong antioxidant capacity even after storage of 24 weeks at ambient temperature.