73D-28 |
Oxygen permeability and mechanical properties of plasticized beta-lactoglobulin films |
R. SOTHORNVIT and J. M. Krochta. Biological and Agricultural Engineering, University of California, Davis, Davis, CA 95616 Plasticizer is of importance to increasing protein film flexibility and processability, by reducing hydrogen bonding between protein chains which causes the film brittleness. No research has been done on plasticizer composition, size and shape influence on ability to disrupt protein-chain hydrogen bonding, including ability to attract water to protein films. Our objective was to investigate the effect of plasticizer composition, size and shape on beta-lactoglobulin (b-Lg) film mechanical properties and oxygen permeability (OP) using both qualitative and quantitative approaches. Aqueous b-Lg solutions (10% w/w) were heated at 90oC for 30 min and then different amounts of plasticizer [glycerol (Gly), sorbitol (Sor), Sucrose (Suc) and polyethylene glycol at MW 200 and 400 (PEG 200 and PEG 400)] were added and the solution degassed. Film solutions were measured onto HDPE plates and placed on a leveled surface at RT until they dried into films. An Instron machine and an Ox-tran 2/20 (ML system) were used to determine film mechanical properties and OP, respectively, at 50% RH and 23oC. Plasticizer type and amount had significantly different effects on film mechanical and OP properties. The smaller MW and straight-chain plasticizers apparently had easier access to the protein chains, because they produced greater film flexibility and higher OP than plasticizers with larger MW or ring structure. Ratios between plasticizer efficiencies for mechanical and OP properties of b-Lg films were defined as plasticizer efficiency ratios (kEM/kOP and kTS/kOP) and determined for each plasticizer. The plasticizer efficiency ratios found were in the order Suc > Sor > Gly > PEG 200 > PEG 400. Empirical equations involving plasticizer efficiencies (k values) for film mechanical and OP properties and the plasticizer efficiency ratios between mechanical and OP properties are useful tools to provide a desirable b-Lg film properties.
Session 73D, Food Packaging
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