The Role of Copper in Protein Foams

Chefs have known that whipping egg white proteins (EWP) in a copper bowl will improve foam stability. The improved stability is attributed to a copper–conalbumin complex or alteration of sulfhydryl reactivity. Whey proteins bind copper and show copper-induced changes in disulfide bonds; therefore, they may also be responsive to whipping in a copper bowl. EWP and whey protein isolate (WPI) solutions were whipped in the presence of 1 mM CuSO₄ or in a copper bowl with and without sugar followed by overrun and yield stress measurements and angel food cake formation. Dilational elasticity and surface tension were also measured for WPI solutions. Whipping in a copper bowl or adding 1 mM CuSO₄ significantly improved stability of EWP foams while having no effect on WPI foams. Copper caused disulfide-linked dimer formation of β-lactoglobulin and decreased dilational elasticity and surface tension, but these modifications were insufficient to change the bulk properties of foams. The addition of 10 mM CuSO₄ to WPI solutions was sufficient to increase foam stability to levels similar to EWP; however, the more stable foams formed less stable cakes. It was concluded that the effect of whipping in a copper bowl on foam properties is mainly dependent on the specific proteins forming the foam. Paper no. FSR-07-29 of the Journal Series of the Department of Food Science, North Carolina State University, Raleigh, NC 27695-7624. Presented at the 2nd International Symposium: Delivery of Functionality in Complex Food Systems: Physically-inspired Approaches From Nanoscale to Microscale, October 8–10, 2007.