Whey protein improves the stability of C-phycocyanin in acidified conditions during light storage.

C-phycocyanin is a bright blue natural colorant used in food and beverage applications. However, its color stability is poor in acidic conditions under exposure to light. In this work, we study the use of whey protein isolate (WPI) to protect C-phycocyanin from color degradation. Low concentration (0.05-0.1%) WPI addition delayed (~2 days) the color degradation of C-phycocyanin at pH 3.0 over 5-day storage in light. However, the color degradation was aggravated adversely during 5-day light storage when C-phycocyanin mixed with a higher concentration (~1%) of WPI degraded after heat-treatment. The Fourier transform infrared and fluorescence spectroscopy confirmed that structural changes (e.g., alpha-helix protection and transformation from alpha-helix to beta-sheet) of C-phycocyanin due to interaction with WPI. These results, along with quartz crystal microbalance with dissipation technology outcomes, suggest that a low concentration of WPI may help protect C-phycocyanin's secondary structure from becoming damaged during light storage, preventing its color degradation.