Kinetic modelling of Amadori N -(1-deoxy-D-fructos-1-yl)-glycine degradation pathways. Part I */Reaction mechanism Sara I.F.S. Martins, a Antonius T.M. Marcelis, b Martinus A.J.S. van Boekel a, * a Department of Agrotechnology and Food Sciences, Product Design and Quality Management Group, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands b Department of Agrotechnology and Food Sciences, Organic Chemistry Group, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands Received 11 December 2002; accepted 11 April 2003 Abstract The fate of the Amadori compound N -(1-deoxy-D-fructos-1-yl)-glycine (DFG) was studied in aqueous model systems as a function of pH and temperature. The samples were heated at 100 and 120 8C with initial reaction pH of 5.5 and 6.8. Special attention was paid to the formation of the free amino acid, glycine; parent sugars, glucose and mannose; organic acids, formic and acetic acid and a-dicarbonyls, 1- and 3-deoxyosone together with methylglyoxal. For the studied conditions decreasing the initial reaction pH with 1.3 units or increasing the temperature with 20 8C has the same effect on the DFG degradation as well as on glycine formation. An increase in pH seems to favour the formation of 1-deoxyosone. The lower amount found comparatively to 3-deoxyosone, in all studied systems, seems to be related with the higher reactivity of 1-deoxyosone. Independently of the taken pathway, enolization or retro-aldolization, DFG degradation is accompanied by amino acid release. Together with glycine, acetic acid was the main end product formed. Values of 83 and 55 mol% were obtained, respectively. The rate of parent sugars formation increased with pH, but the type of sugar formed also changed with pH. Mannose was preferably formed at pH 5.5 whereas at pH 6.8 the opposite was observed, that is, glucose was formed in higher amounts than mannose. Also, independently of the temperature, at higher pH fructose was also detected. pH, more than temperature, had an influence on the reaction products formed. The initial steps for a complete multiresponse kinetic analysis have been discussed. Based on the established reaction network a kinetic model will be proposed and evaluated by multiresponse kinetic modelling in a subsequent paper. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Amadori compound; N -(1-deoxy-D-fructos-1-yl)-glycine; Maillard reaction; Multiresponse kinetic analysis 1. Introduction Since Hodge 1 presented the first coherent Maillard reaction scheme in 1953, the Amadori compound N - substituted 1-amino-1-deoxy-ketose is believed to be the key intermediate in the early stages of the reaction. The accepted mechanism for the formation of Amadori compounds involves the initial reaction of a reducing sugar with an amino group to give the corresponding glycosylamine, that rearranges to the corresponding ketoseamine, also known as the Amadori rearrangement product (ARP). The set of reactions that occurs there- after is of great importance in the processing of foods for the production of aroma, taste and colour. Further- more, evidence strongly suggests that this intricate reaction cascade is involved in the pathology of diabetes and ageing. 2 Due to the complexity of products that are formed from the degradation of the ARP, recent studies used the Amadori compound as the initial reactant. 3  6 These studies showed that the 1,2- and 2,3-enolizations of Amadori compounds under acid/base catalysis condi- tions initiate b-elimination reactions, which eventually lead to the formation of reactive intermediates (Scheme 1). The degradation of N -(1-deoxy-D-fructos-1-yl)-gly- cine (DFG) (1) by 1,2-enolization (pathway A) and 2,3- * Corresponding author. Tel.:  /31-317-482520; fax:  /31- 317-483669. E-mail address: tiny.vanboekel@wur.nl (M.A.J.S. van Boekel). Carbohydrate Research 338 (2003) 1651  /1663 www.elsevier.com/locate/carres 0008-6215/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0008-6215(03)00173-3