The Effect of Thermal Treatment and Storage on the Stability of Ascophyllum nodosum Extract

Macroalgae-derived polyphenols have been considered as a potential source of food supplements that can enhance the nutritional value and extend the shelf life of foods. However, thermal treatment during food processing as well as storage might induce the degradation of some bioactive compounds in the extract. In the present study, the stability of the extract from the edible brown algae Ascophyllum nodosum was evaluated under thermal treatment (40–90 °C). Significant differences in TPC, RSC, and antioxidant activity were found during all treatments. The total phenol content (TPC) and antioxidant activity (DPPH scavenging activity) decreased up to 5% and 10%, respectively, after 6 h of thermal treatment, while the reducing sugar content (RSC) increased from 8 to 35% as the temperature increased from 40 to 90 °C. The stability of the extract during storage with or without exposure to air was evaluated at room temperature (25 °C) and low temperature (4 °C) for 108 h, and the influence of the solvent used to contain the extract has been investigated by studying both concentrated and non-concentrated extracts. It was found that the extract stored at 4 °C without exposure to air had a negligible TPC change, while RSC increased in the extract exposed to air, suggesting that oxygen in the air might accelerate polysaccharide degradation during storage. Antioxidant activity of extracts remained constant at both 4 and 25 °C, regardless of exposure to air.