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

Korbel E., Attal E.H., Grabulos J., Lluberas E., Durand N., Morel G., Goli T., Brat P.. 2012. In : Jana Pulkrabová, Monika Tomaniová, Vanda Godulová, Karel Cejpek and Jana Hajslová. Chemical reactions in foods VII. Book of abstracts, 7th International Conference on Chemical Reactions in Food, Prague, Czech Republic, November 14-16, 2012. Prague : Institute of Chemical Technology, p. 67-67. International Conference on Chemical Reactions in Food. 7, 2012-11-14/2012-11-16, Prague (Tchèque, République).

Mango fruit (Mangifera Indica L.), one the most important tropical fruits, is highly perishable and required therefore to be quickly stabilized. Among the technological solutions, drying appears to be a very promising stabilization solution. The traditional drying of mango can be separated in two phases: the first one carried at ?80°C for 10 to 12 hours makes the water activity (aw) decline from 0.99 to 0.8. During the second phase, the drying temperature is reduced to 40°C until the aw reach ~ 0.5. These conditions are highly favorable to enzymatic (1st drying) step and non-enzymatic (Maillard) reactions (2nd drying step). The focus of this work was therefore to highlight the coupled effects of aw and T°C on the development of these classes of reactions all along the process. For a global comprehension of the browning of mango during the drying process, we used lyophilized powder reconstituted to the required water activities and thenafter heated during various times. Several precursors (reducing sugars) and intermediary products of the Maillard reaction (5-hydroxymethyl furfural (5-HMF) and other neo-formed furan- and pyran-derivated compounds) were analyzed to estimate non-enzymatic reaction intensity while polyphenoloxidase (PPO) and peroxidase (POD) were associated to enzymatic browning. We confirm that the highest production of 5-HMF as a marker of the Maillard reaction mainly occurs for water activities of 0.6. Kinetic analysis of Maillard reactions precursors and intermediate products in model mango system permit to identify asparagine and glutamic acid as limiting precursor, and 5-HMF among significant awdependent products. Furoic acid and furfural linked to the ascorbic acid degradation followed the same tendency. The impact of the water activity on the thermal degradation of PPO and POD was proved to be strongly different. After 4h at 40°C, the PPO, POD remaining activity at aw 0.65 was 22 and 97% respectively while these values being 82 and 64% at 0.98 respectively. As a conclusion, we identified critical points in the drying process making the fruit turn to brown and thus improved our global comprehension of the involved mechanisms. The approach we developed could be useful to help to understand the biochemical mechanisms in complex matrices such as fruit and vegetables. (Texte intégral)

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