Surface properties of edible, biopolymer coatings for foods: Color, gloss, surface energy and adhesion

Whey protein isolate (WPI) coatings were found to have greater color stability than shellac or whey protein concentrate (WPC) coatings. Maillard browning was responsible for the increased yellowing rate of WPC coatings. The results indicate that WPI coatings can be used in place of shellac or zein coatings, with improved color stability. WPC coatings could be used to promote color development a food product, when desired.; WPI coatings have gloss properties equal to or better than shellac, zein, dextrin and hydroxpropyl methylcellulose (HPMC) coatings. WPI coatings had stable gloss values at 52, 75 and 95% relative humidity (RH). After a few hours at 95% RH, shellac and zein coatings turned white, while dextrin and HMPC coatings became liquefied and tacky, respectively. WPI and shellac coatings maintained a high gloss after 7.6 months of storage at 23°C and 75% RH. For lipid dispersion systems, WPI coatings maintained a higher gloss than shellac films at equal lipid contents (on a dry film basis).; The surface energy properties of biopolymer coatings were determined from contact angle measurements using thermodynamic models. Both the properties of the contact liquids and the model used influenced the calculated surface energy properties of WPI coatings. Increasing glycerol plasticizer content of WPI formulations increased coating swelling, but not overall coating polarity. Calculated surface energy properties of hydrophobic coatings were less influenced by contact liquid properties then for hydrophilic coatings. Surfactants increased surface polarity due to surfactant migration. Standard contact angle methods are limited to gross estimates of surface energy properties when used for hydrophilic coatings.; The adhesion of hydrophilic WPI coatings to low surface energy substrates was equal to hydrophobic shellac and greater than corn zein coatings. Glycerol plasticizer had a small effect on WPI adhesion to acrylic substrates, while Span 20 surfactant reduced WPI adhesion to polypropylene. Surface energy properties of model acrylic and polypropylene surfaces approximated those of dark chocolate and peanuts, respectively, Water-based WPI coatings have adhesion to low-surface-energy solids equal to or greater than shellac and zein coatings.