Physical properties of edible films and their components

Edible films can help stabilize or improve food products by decreasing moisture and gas transmission, retaining volatile components, enhancing food appearance or by improving the mechanical properties of foods. Commercial utilization of these films is limited, party because information about their properties is relatively meager. This work was undertaken to increase knowledge regarding the physical properties of edible films.; The first study involved examining the water vapor (WV) permeance of lipid and lipid-hydrocolloid films exposed to relative humidity gradients of 100-0%, 100-50%, 100-65%, and 100-80%. The lipids used were beeswax or a blend of beeswax and acetylated monoglycerides. Hydrocolloids used were methylcellulose, carboxymethylcellulose, or ethylcellulose. All films, except those containing ethylcellulose, exhibited increased WV permeance as the relative humidity gradient was lessened by raising the low-end relative humidity. This increase in permeance is attributed to hydration and swelling across the entire film thickness, thus facilitating water movement through the film. Because of its extreme hydrophobicity, ethylcellulose likely lessened this swelling.; In the second study, WV and oxygen permeabilities of beeswax, candelilla wax, carnauba wax, and microcrystalline wax were determined. The two plant waxes, candelilla and carnauba, exhibited excellent barrier properties to WV. Differences in permeabilities among the waxes are attributed to differences in chemical composition and crystallinity.; In the last two studies, the physical properties of methylcellulose were examined. The effects of drying temperature, solvent composition, and plasticizers on film crystallinity, WV and oxygen permeability, and mechanical properties were determined. Methylcellulose solutions containing a solvent consisting of 75% water-25% ethanol resulted films within significantly ({dollar}alpha{dollar} = 0.05) lower oxygen permeability, and greater tensile strength and percent elongation than films prepared from solvents of 100% water, 50% water-50% ethanol, or 25% water-75% ethanol. The differences may be attributed to greater association of methylcellulose segments by hydrogen bonding in the film prepared from a solvent containing 25% ethanol. Polyethylene glycol 400 and glycerol were the most effective plasticizers in methylcellulose films. Within a homologous series of plasticizers, such as polyethylene glycol, plasticizer efficiency decreased with increasing molecular weight.