Performance of alginate films for retention of l-(+)-ascorbic acid

Abstract

In view of acting as controlled delivery systems for nutritional supplementation, therapy or antioxidant activity at interfaces, alginate films of different copolymer composition and glycerol plasticizer levels were developed in the presence of Ca2+ for achieving higher stability of l-(+)-ascorbic acid (AA). The ability of the alginate network to preserve AA from hydrolysis, tested by storage under vacuum at 25 °C, only decreased with the relative humidity (RH) increase when alginates were mainly constituted by guluronic–guluronic acid blocks (GG), whereas also decreased with the glycerol level increase when mannuronic–mannuronic acid (MM) and/or alternating guluronic–mannuronic (GM + MG) flexible blocks were present in higher proportions. This result could be probably related to the lower capability of the latter alginate block compositions to immobilize water in the network as they are not able to constitute Ca2+ mediated junction zones where water molecules are highly retained. Films also studied under air storage showed that even at less favorable conditions of RH and glycerol levels, both GG and GM + MG enriched alginate networks in general preserved AA from oxidation. It also demonstrated that hydrolysis is the principal way by which AA is lost when supported in films.