Effects of film constituents on packaging-relevant properties of sodium caseinate-based emulsion films
The objective of this study was to examine the effects of the plasticizer type (sorbitol or glycerol) and lipid concentration (oleic acid or oleic acid-beeswax mixtures) on sodium caseinate (NaCas)-based films and to investigate how, and to which extent, these parameters are affecting the technofunctional properties of NaCas-based films. Additionally, we intended to demonstrate the antioxidant potential of quercetin as a component of the described formulations. Films prepared from the different composed emulsions were characterized in terms of selected packaging-relevant properties. The results showed that the type of plasticizer and the lipid concentration had significant effect on the technofunctional properties of NaCas-based films. Contact angle measurement and evaluation of the SFE revealed rather hydrophilic than hydrophobic surfaces. Determination of the WVTR showed a significant influence (p < 0.05) of the type of plasticizer towards WVTR. WVTR was clearly decreased for sorbitol-plasticized films. On the contrary, the influence of the lipid concentration was also significant (p < 0.05), but not as clear as the plasticizer effect. However, at 10% (w/w) beeswax (BW) addition, there was a sharp drop in WVTR visible for glycerol-plasticized films. Measurement of the OP did not yield as clear results as suggested in preliminary test series. Although, we did not conduct systematic studies regarding the effect of the antioxidant towards the OP we showed the antioxidant potential of the described compositions. Results for the mechanical performance showed a significant influence (p < 0.05) of the type of plasticizer and lipid concentration. YM and TS values were clearly higher for sorbitol-plasticized films whereas E% values were lower for sorbitol-plasticized films. Regarding the effect of the lipid concentration on the mechanical performance, no apparently visible trend could be identified. Light transmittance measurement revealed that in terms of UV-absorptivity at wavelengths between 300 nm and 400 nm, the incorporation of quercetin led to promising barrier properties against UV-light.