Biodegradable Films from Spray Dried Starch Inclusion Complexes with Bioactive Compounds—The Effect of Glycerol and pH

Abstract

In the present study, thermoplastic films are prepared using spray dried starch-bioactive compound systems powders with different concentrations of glycerol (20% or 40%). The starch-based films are produced by casting after dissolution under neutral (pH 7) or alkaline conditions (pH 12). Results reveal that elevated glycerol contents lead to increased moisture and hygroscopicity which is related to the availability of more ─OH groups. ANOVA shows that the glycerol concentration, the pH value, and the interactions of bioactive compounds with glycerol, bioactive compounds with pH, and glycerol with pH, influence significantly the mechanical properties of the thermoplastic starch films. Young's modulus of elasticity increases alongside with glycerol content, indicating improved flexibility of the films. Stress decreases with higher glycerol contents and lower pH while strain on the contrary, increases as the glycerol and pH increase in the films. Significant differences are also observed in water adsorption and water vapor transmission rate values. As expected, water adsorption increases with increasing relative humidity (RH) with the glycerol content positively affecting the water uptake by the films. Microscopic examination indicates the homogeneous distribution of the bioactive compounds in the matrix of the films.