Spectrophotometric analysis of polysaccharide/milk protein interactions with methylene blue using independent components analysis
Résumé
Interactions between xanthan gum, carrageenan, guar gum and milk protein were studied under various conditions of ionic strengths, temperature and pH. The proposed methodology was to examine the associative interactions by using a methylene blue (MB) spectrophotometric method combined with data analysis by a chemometric method. Independent Components Analysis (ICA) simplified the interpretation of the spectrophotometric results by decomposing absorbance spectral data into "pure signals" that could be related to chemical compounds. Addition of milk protein to MB/xanthan gum or carrageenan solution gave rise to spectral changes indicating electrostatic interactions between positively charged regions of milk protein and anionic polysaccharides at neutral pH and low ionic strength. Thus, it has been shown that negative polysaccharides are able to interact with milk proteins only in absence of NaCl. On the other hand, it was shown that no attractive interactions were established in neutral guar gum/milk protein systems, which highlighted the contribution of the charge density to the interactions. Through acidification, associative interactions between xanthan gum and milk proteins were strongly enhanced as shown by changes in the IC proportions. Therefore, ICA proved to be an efficient tool to facilitate interpretation of spectrophotometric data and identify associative interactions.