Release of fireweed extract (Epilobium angustifolium L.) from corn starch- and methylcellulose-based films - a comparative study

Abstract The release and antioxidant properties of edible films based on corn starch (CS) and methylcellulose (MC) incorporated with increasing concentrations (0, 0.0125, 0.025, and 0.05%) of powdered fireweed extract (FE) were characterized and compared. The findings were discussed in terms of the water affinities of the films. MC produced a carrier with higher swelling capacity (337-423%) compared to CS (102-135%). Moreover, the MC films were dissolved rapidly and completely in water, while the solubility of CS films reached a constant value of ∼30%. The gradual rise in the FE concentration increased the release rate from both carriers. Probably due to the highest number of parameters, the Weibull models showed great potential to be fitted to most FE release patterns. Based on the half-release times (t50%), the 0.0125 and 0.025% FE-supplemented CS films ensured a ∼10 (t50%=48.48 min) and ∼1.5 (t50%=6.30 min) slower release rate than the MC counterparts. This result can be ascribed to the less erodible character of the CS carrier. A high correlation (R2=0.79) was found between film solubility and FE release. The FE release from the CS carrier proceeded through diffusion-controlled transport, while the FE release from the MC films was related to the coupling of Fickian diffusion and the polymer matrix relaxation mechanism. It was found that the 0.05% FE-supplemented MC system, as the most water-swellable, exhibited slower FE migration than the analogous CS film (t50%=3.50 vs. 2.59 min). A high correlation (R2=0.79) was found between the t50% and the antiradical activity of the films.