Whey protein based colloidal gas aphrons combined with solid–liquid extraction as an integrated green separation of phenolics from fruit based by-products

Colloidal gas aphrons (CGA) are microbubbles created by the intense stirring of a surfactant solution that can be used as a separation method for biomolecules. The main objective of this work was to investigate for the first time the use of whey protein as a natural surfactant for CGA generation. Furthermore, their application for separating phenolic compounds from hydroalcoholic extracts obtained from fruit based by-products (grape marc and red goji berry). Additionally, to investigate if this surfactant-rich fraction could confer an advantage in stabilising anthocyanins during storage. First, a hydroalcoholic extract was obtained from each feedstock; then whey protein isolate (WPI) generated CGA were applied and compared with Tween 20 generated CGA. Recovery performance was assessed based on total phenolics, flavonoids, and antioxidant capacity. CGA generated with a 1.5 % WPI displayed comparable characteristics (gas hold-up and stability) to those generated with Tween 20 (10 mM). The CGA separation process with WPI led to a recovery of up to 97 % of phenolic compounds but a loss of antioxidant capacity under the tested conditions. Hydrophobic interactions as well as hydrogen bonding between phenolics and WPI could be responsible for the successful separation that could also hinder the radical scavenging activity. In contrast, these interactions could be responsible for the stabilising effect on anthocyanins observed during storage. Overall, CGA generated with WPI have resulted in an integrated separation method that by combining it with hydroalcoholic extraction leads to the effective separation of phenolics and their pre-formulation in a whey protein rich solution with stabilisation effect.