Encapsulated polyphenolic-rich raspberry pomace extract has a potential application as a natural food preservative

This study aimed to encapsulate polyphenolic-rich extracts from raspberry pomace via freeze-drying and evaluate the effect of gum arabic, maltodextrin and waxy starch as a drying aid on their physicochemical, rheological, and bioactive characteristics. Raspberry pomace was extracted using 70% ethanol and concentrated to 12 °Brix. The concentrated extract was then encapsulated using 10% different carrier agents, including maltodextrin, gum arabic and waxy starch, followed by freeze-drying (-55°C; 0.1 mbar) to produce the powder. The powders showed significant differences (p<0.05) in all the variables analysed: solubility, water holding capacity (WHC), Carr index (CI) and Hausner ratio (HR), total phenolic content (TPC), total anthocyanin content (TAC) and ferric reducing power (FRAP). Gum arabic and maltodextrin encapsulated powder presented a high solubility (98.99 and 97.60%), lowest with waxy starch (64.26%). Similarly, powders obtained from gum arabic and maltodextrin had the highest water-holding capacity (0.98 and 0.92 g g^-1), respectively. Maltodextrin encapsulated powder presented an intermediate cohesiveness (17.74%) and a fair to good flowability (1.22). A higher total phenolic content was recorded for powders produced with maltodextrin (87.32 mg GAE 100 g^-1 DM) followed by waxy starch (74.93 mg GAE 100 g^-1 DM) and gum arabic (33.63 mg GAE 100 g^-1 DM). Higher total anthocyanin content was recorded for powders produced with maltodextrin (18.36 mg C3gE 100 g^-1 DM) followed by waxy starch (17.49mg C3gE 100 g^-1 DM) and gum arabic (17.40 mg C3gE 100 g^-1 DM) respectively. FRAP activity was high for powders produced with gum arabic (39.27 mM TE g^-1 DM) followed by waxy starch (33.90 mM TE g^-1 DM) and maltodextrin (31.40 mM TE g^-1 DM). Given its favourable rheological and functional properties, the powder produced with maltodextrin presented to be the best suitable carrier agent for the encapsulation of raspberry pomace extracts for application as food preservation.