EFFECT OF PH ON PROPERTIES OF WHEAT GLUTEN AND SOY PROTEIN ISOLATE FILMS

Soy protein isolate (SPI) and wheat gluten (WG) films can be cast from appropriate solvent systems. Such films can find use as edible or nonedible food packaging materials. The effect of pH of WG and SPI film-forming solutions on film formation, tensile strength (TS), percentage elongation at break (E), and water vapor permeability (WVP) was investigated. WG films formed within pH 2-4 and 9-13, whereas SPI films formed within pH 1-3 and 6-12. Film formation was inhibited by poor protein dispersion around the isoelectric pH region of SPI (pH 4.5) and WG (pH 7.6). SPI films prepared from pH 6 to 11 had significantly (P < 0.05) higher TS, higher E, and lower WVP than films from pH 1 to 3. WG films produced under alkaline conditions had significantly (P < 0.05) higher TS than films processed under acidic conditions.