The stabilization of food grade copper-chlorophyllin in low pH solutions through association with anionic polysaccharides

Abstract

This work investigates the potential for anionic polysaccharides, such as alginate and xanthan gum, to impart solution and color stability to dilute solutions of copper chlorophyllin (Cu-ChP) buffered at acidic pH. Under cold storage, both polysaccharides tested were shown with sufficient loading to mitigate Cu-ChP aggregation at pH 3.0 and 5.0; xanthan gum use required lower loadings than the sodium alginate tested. Analysis of polysaccharide stabilized Cu-ChP solutions by dynamic light scattering suggests complex formation does occur; this is likely driven by electrostatic interactions between copper cations coordinated at the pigment core and the heavily anionic surfaces of the polyccharide matrices created by the large number of uronic acid substituents on the hydrocolloids.. During accelerated stability testing at elevated temperature (40 °C), pure Cu-ChP controls readily aggregated and lost the solution color distribution, while both polysaccharides maintained both solution and color stability through the initial 5-day test; xanthan gum showed the best promise in this regard, maintaining solution stability and most of the original color through 14 days at both pH tested. CIE a* and b* color data further show more than half of the original green tones and nearly all of the original yellow tones are preserved during heating with either polysaccharide present. Despite this, the slight transition in overall color towards more olive-green tones suggest a level of pheophytinization (metal ion loss) occurs. Finally, quartz crystal microbalance with dissipation monitoring (QCM-D) provides initial insight into the stabilization of Cu-ChP solutions by these polysaccharides and suggests that the weaker, yet stable, association of the pigment source with xanthan gum compared to the sodium alginate tested may be key to its superiority as a stabilizer.