Whey protein coating efficiency on surfactant-modified hydrophobic surfaces

Whey protein oxygen-barrier coatings on peanuts are not effective, due to incomplete peanut-surface coverage, as well as some cracking and flaking of the coating. Addition of sorbitan laurate (Span 20) in the whey protein coating solution up to the critical micelle concentration (cmc) of 0.05 % (w/w) significantly improved coating coverage to 88 % of the peanut surface. Increasing the Span 20 concentration in the coating solution to 3 times the cmc (0.15 % w/w) produced a substantial increase in peanut surface energy (> 70 dyn/cm), indicating adsorption of the surfactant to the peanut surface. With this level of Span 20, the whey protein coating coverage on peanuts increased to 95 %. These results suggest that a concentration of surfactant above the cmc in the coating solution is required for formation of self-assembled structures of surfactant molecules on peanut surfaces, which significantly increases the hydrophilicity, and thus coatability, of peanut surfaces.