Impact of temperature and water activity on enzymatic and non-enzymatic reactions in reconstituted dried mango model system

Mango fruit (Mangifera indica L.) is highly perishable and must therefore be quickly stabilized. Drying appears to be one of the most promising stabilization solutions. The traditional mango drying process can be divided into two phases: the first, which is performed at *80 _C for 10 to 12 h, sees water activity (aw) decline from 0.98 to 0.8. During the second phase, the drying temperature is reduced to 50 _C until aw reaches *0.6. These conditions are highly favorable to enzymatic and non-enzymatic reactions (1st and 2nd step, respectively). The focus of this work was therefore to highlight the effects resulting from the coupling of aw and temperature on the development of these classes of reactions during the whole process. Several precursors (reducing sugars and amino acids) and intermediary products of the Maillard reaction were analyzed to estimate non-enzymatic reaction intensity when polyphenoloxidase (PPO) was associated with enzymatic browning. We were able to show that the highest production of 5-hydroxymethyl furfural (5-HMF) as a Maillard reaction marker occurs mainly for an aw of 0.6. Kinetic analysis of Maillard reaction precursors and intermediate products in model mango system helped us identify asparagine and arginine as limiting precursors, and 5-HMF as a significant aw-dependent product. The impact of the aw on the thermal degradation of PPO proved to be radically different. After 8 h at 40 _C, the PPO was almost totally inhibited if this treatment is conducted on a sample at aw 0.65, while residual activity was estimated to be 69.4 % for a sample at aw 0.98. (Résumé d'auteur