Abstract
The objective of this work is to study the effect of the rapeseed oil content on the physical properties of whey protein emulsion films. For this purpose, whey protein films with the addition of 0, 1, 2 and 3% of rapeseed oil, and glycerol as a plasticizer were obtained by the casting method. Film-forming emulsions were evaluated and compared using light scattering granulometry. The Sauter mean diameters (d32) of lipid droplets in film-forming solutions showed an increasing trend when increasing the oil volume fractions. The inclusion of rapeseed oil enhanced the hydrophobic character of whey protein films, reducing moisture content and film solubility in water. All emulsified films showed high lightness (L*≈90). Parameter a* decreased and parameter b* and total colour difference (∆E) increased with the increase of the volume fractions of oil. These results were consistent with visual observations; control films were transparent and those containing oil opaque. Water vapour sorption experimental data at the full range of water activity values from 0.11 to 0.93 were well described with Peleg's equation (R2≥0.99). The tensile strength, Young's modulus and elongation at break increased with the increase of rapeseed oil volume fraction, which could be explained by interactions between lipids and the protein matrix. These results revealed that rapeseed oil has enormous potential to be incorporated into whey protein to make edible film or coating for some food products. The mechanical resistance decreased with the addition of the lipids, and the opacity and soluble matter content increased.
Highlights
Biopolymers from various natural resources such as proteins and polysaccharides have been considered attractive alternatives for non-biodegradable petroleum-based materials [1]
Whey protein films were prepared with 0, 1, 2 and 3 % of rapeseed oil, which is less than the literature findings for other hydrocolloid films with the volume fraction of up to 20 % of liquid oil [1,20,31,32]
Equilibrium moisture contents of analyzed whey protein films incorporated with rapeseed oil remained constant and did not change with an increase in temperature (Fig. 2)
Summary
Biopolymers from various natural resources such as proteins and polysaccharides have been considered attractive alternatives for non-biodegradable petroleum-based materials [1]. Protein-based edible films have interesting properties, and various materials have been tested including wheat gluten [2], whey protein [3], soya protein [4], casein [5], collagen [6], gelatin [7], corn zein [8], egg white proteins [9], quinoa [10], myofibrillar proteins [11] and other proteins [12] Milk proteins, such as whey proteins, have special properties that make them highly suitable for obtaining edible films. Their excellent nutritional value and numerous functional properties such as solubility in wa-
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