Age- induced Changes in Some Properties of Plasticized Soybean Protein Concentrate Films Obtained by Casting and Compression Molding

E.M. CIANNAMEA; L. GONZALEZ GRANADOS; L. NEIRA HAZIME; J. MARTUCCI; P.M. STEFANI; R.A. RUSECKAITE

Barelona

Congreso; Third International Symposium Frontiers in Polymer Science; 2012

Ageing of soybean protein concentrate (SPC) plasticized different amounts of glycerol (Gly) and processed by casting from film-forming solutions at pH 10 and by intensive mixing followed by compression molding was studied over a period of 120 days. Changes on optical, water resistance, oxygen transmission rate (OTR) , tensile and water vapor permeability (WVP) properties of films during ageing were analyzed. All films lost mass continuously during the entire aging period due to leaching of glycerol as revealed by  infrared spectroscopy. Compressed molding films exhibited lower total matter solubility (TMS) with time  due to the higher contribution of disulphide linkages to film-stabilizing forces. Un-aged SPC films obtained by compression molding had higher tensile strength (TS), elastic modulus and elongation at break (e) than those produced by casting in agreement with the higher total moisture content of compressed molding films. TS values increased progressively during aging, irrespective of  the processing method and plasticizer concentrations in the films, with the concomitant reduction in elongation. Therefore films became stiffer and less flexible. The largest changes were observed in casting films with 50%Gly which enhanced the mobility of the protein chains. WVP values of compression molding unaged films were lower than those of casting films and insignificant changes with time were observed, whereas OTR slightly increased may be due to conformational of soybean protein upon ageing.