Preparation and mechanical properties of edible pectin-soy flour films obtained in the absence or presence of transglutaminase.

Whole soy flour and apple pectin were used as raw materials for producing hydrocolloid edible films. The best ratio between the two components (2:1 mg cm(-2), pectin-soy flour) was determined in order to obtain films which could be perfectly handled for their consistence. Films were also prepared in the presence of transglutaminase, an enzyme able to produce isopeptide bonds among the soy polypeptide chains. The latter films showed a smoother surface and higher homogeneity, as demonstrated by microstructural analyses, whereas studies on the mechanical properties indicated that transglutaminase increased their strength and reduced their flexibility. Our results suggest a possible use of the transglutaminase polymerized pectin-soy protein films as edible food or drug coatings.