Incorporation of phenolic compounds, rutin and epicatechin, into soy protein isolate films: Mechanical, barrier and cross-linking properties

Edible films prepared from soy protein isolate (SPI), with and without the phenolic compounds, rutin and epicatechin, as cross linking agents, were tested for their mechanical, optical and water vapour barrier properties. The addition of rutin significantly increased puncture strength (9.3 N) over SPI alone (6.4 N) whereas epicatechin had no effect. Tensile strengths of SPI films with rutin and epicatechin were similar (35.1 MPa and 22.1 MPa, respectively) and significantly stronger than films without added phenolics (9.3 MPa). SPI films without phenolics showed the greatest flexibility, as measured by tensile elongation. The addition of epicatechin was found to increase water vapour permeability significantly to 2.3 g mm/m2 h kPa from 1.7 g mm/m2 h kPa for SPI alone whereas rutin decreased water vapour permeability to 1.2 g mm/m2 h kPa. Films without phenolics had lower opacity values than had those with phenolics. Findings indicate that rutin and epicatechin may be used as a natural means for improving specific properties of SPI films.