Browning, enzymatic water activity

To fulfill the needs for long term stability of a biological material, the optimum range of water activity lies between 0.20 and 0.35, This area represents the best compromise between lipid oxidation and non-enzymatic browning. Enzymatic browning is suppressed under these conditions, and growth of microorganisms is impossible. 

Bell, L.N. Kinetics of non-enzymatic browning in amorphous solid systems distinguishing the effects of water activity and glass transition. Food Res. Int., 28, 591,1996. 

The present chapter deals with the study of edible films based on deacylated and/or acylated forms of gellan gum to support L-(+)-ascorbic acid (AA) in view of natural antioxidant protection of foods, by leveraging its activity as a vitamin in the human metabolism. Kinetics of AA-destruction and subsequent non enzymatic browning development were studied in the films stored at constant temperature (25 C) and relative humidity (33.3, 57.7 or 75.2%) and their relationship with the microstructure, at the macromolecular and molecular levels, was also analyzed with the purpose of ensuring a better AA retention as well as lower browning rate as a consequence of controlled water mobility in the polymeric networks. 

---