Enhancing hydrophobic and antioxidant properties of whey protein films through the inclusion of oil and oleogel sourced from spent coffee grounds

Abstract

In this study, whey protein edible films with improved hydrophobic and antioxidant properties were developed through the addition of oil-based components deriving from spent coffee grounds (SCG). Initially, the recovery of the oil fraction from SCG was performed using conventional and “green” extraction techniques. Results showed that a higher recovery yield (77.4%, w/w) of SCG oil was achieved through the supercritical CO2 extraction process, than the conventional one with hexane (59.8%, w/w). Thereafter, SCG oil and SCG oil-based oleogels, using beeswax and candelilla wax as oleogelators, were incorporated into whey protein concentrate films. Incorporation of oil and oleogels into the film matrix had an obvious effect on their hydrophobic character. More specifically, solubility, swelling index and water vapor permeability of films decreased significantly (p < 0.05) as the concentration of oil and oleogels was increased. The most significant (p < 0.05) impact on the swelling index was observed in films containing oleogels as opposed to oil. In fact, the inclusion of 7.5% of SCG-beeswax oleogel, led to the highest reduction (70%) of the swelling index of films. Likewise, antioxidant activity of films was enhanced by the inclusion of SCG oil-based components, due to the presence of antioxidants in SCG oil. Moreover, films presented a time-dependent antioxidant activity, indicating that film structure allowed for a controlled and gradual release capacity of the antioxidants over the time. Eventually, this study demonstrated that oil-based materials derived from food waste can be used as additives, to improve the water-barrier and antioxidant properties of films.