Basic knowledge of edible films improves their utility.

There continues to be an interest in incorporating natural constituents into food systems. Edible film packaging systems are an example of such an approach. We all know that edible films used to encapsulate food and pharmaceutical products are able to increase the quality, safety and storage stability of these products. Scientists in Ireland wanted to investigate the effects of water and plasticizers--glycerol, xylitol and sorbitol--on the physical and mechanical properties of potato starch-based edible films.

The researchers prepared film solutions by mixing a polyol and potato starch into water which they heated to gelatinize starch. Starch concentration (40% to 70% of solids) totaled 5% (w/w) of the overall water content independently of polyol concentration, which was 30% to 60% of solids.

Starch-based films were made by casting and evaporating water at 35 C. Water sorption properties of various films were obtained after storing dehydrated samples in vacuum desiccators at relative humidities of 11% to 86% at 25 C. Researchers used scanning calorimetry to obtain glass transition temperatures. A commercial universal testing machine measured mechanical properties for starch-based films that had various amounts of plasticizers stored at relative humidities of 33%, 54% and 76%.

The investigators found that water sorption of films increased with increasing relative humidity. Steady-state water contents were reached within 48 hours. At constant starch-plasticizer ratios, water contents were lower in films containing higher molecular weight plasticizers.

Glass transition temperatures decreased as a result of plasticization as polyol content or water content increased. Values of Young's modulus decreased with increased polyol content. There was a concurrent increase in the elasticity of films. Both the increased polyol and water content increased elongation at break and decreased tensile strength. At a constant starch-polyol ratio, glycerol lowered the Young's modulus most effectively. Sorbitol was the least efficient. The effect of plasticizers on elasticity was the greatest for glycerol and the least for sorbitol.

You can use this basic knowledge about the effects of water and plasticizers on the physical and mechanical properties of starch-based edible films when developing these films for food applications.

Further information. Yrjo Roos, Department of Food Science and Technology, University College Cork, Cork, Ireland; phone: [phone]; fax: [phone]; email: [e-mail].