Biopolymer/candelilla wax emulsion films as carriers of ascorbic acid – A comparative study

Abstract

The comparative studies were performed in order to assess the most suitable matrix polymer for ascorbic acid (AA). The antioxidant (0.5, 1.0, 2.0% w/w) was included into sorbitol-plasticized emulsion films based on different biopolymers: carboxymethyl cellulose (CMC), oxidized potato starch (OPS), soy protein isolate (SPI), and gelatin (GEL). AA reduced the mechanical strength of the films in a concentration dependent manner. GEL and CMC produced films with higher mechanical strength and stiffness compared to the plant storage polymers. The moisturizing action of AA inhibited plasticizer recrystallization in the protein-based films. It was found, that non-enzymatic browning of the films prepared at lower pH values (OPS and GEL) was slower than those of casted at higher pH (CMC and SPI). SPI films displayed the most intensive browning development. The highest AA retention was achieved in OPS films, while the lowest in GEL films. The AA stability increased with increasing AA concentration. A significant correlation existed between the antioxidant activity of films and the concentration of AA released into aqueous food simulant. CMC films, due to rapid dissolution, tended to have the highest ferric reducing antioxidant power (FRAP) and antiradical activity. In turn, water-swollen GEL films had the lowest antioxidant activity. Prolonged testing in an emulsified linoleic acid model system revealed that at higher AA incorporation levels the films did not differ in their anti-lipid peroxidation capacity.