Effects of flaxseed oil concentration on the performance of a soy protein isolate-based emulsion-type film

- Soy protein-flaxseed oil films showed a bi-modal droplet size distribution.
- Film strength was greatest in the presence of 5% oil content.
- Water vapour barrier properties were independent of the oil content.
- Films retained less moisture and swelled less as the oil content increased.

Biodegradable edible films have the potential to either replace or reduce the amount of synthetic packaging utilized by the food industry. The overall goal of this research was to investigate the effect of flax seed oil concentration (1-10%) on the mechanical, moisture barrier and swelling properties of soy protein isolate (SPI) (5.0% w/w SPI, 40% w/w glycerol) emulsion-based films. Film forming solutions showed a bimodal oil droplet distribution with peak sizes occurring at < 10 and ~ 100 μm. As the oil content increased, the size distribution shifted towards smaller droplet sizes. An equal size ratio was noted at the 5.0% oil content level. All film forming solutions were pseudoplastic in nature, where viscosity increased from 18 to 58 mPa (at 1 s− 1) as a function of oil content (3% to 10%). Tensile strength of formed films reached a maximum at 5.35 MPa at the 5% w/w oil level, whereas tensile elongation increased from 11.3% to 22.2% with increasing oil content. Puncture strength and deformation, as well as water vapour permeability was relatively independent of the oil content. Moisture content and swelling properties of formed films were found to both decrease from 22.8% to 18.7%, and from 3114% to 1209%, respectively as the oil content was raised from 1 to 10%, and films became darker, redder and more yellow in colour as the percentage of flax seed oil increased.