Solution to Maillard and grilled steak challenge.

Abstract

Today’s solution to the ABC Analytical Challenge is unusual, because there is no answer yet. Let us recall the facts. Maillard processes are famous in science and technology, particularly food and medicine. In fact, Maillard processes are said to be responsible for both good and bad [1]: they contribute to the flavour of some cooked food (particularly meat) but also generate glycation products, which can be bad for our health, as is clearly apparent in the proceedings of the Maillard association (IMARS [2]). It is also true that Maillard processes are “fashionable”: in July 2015, a Google Scholar search for “Maillard reaction” led to more than 45,000 answers (250,000 for “Diels-Alder”), including more than 2 000 results for 2015 only. The same growing trend is also apparent from the Pubmed database (Fig. 1). A variety of aspects and models have been studied but, as said in the Maillard Challenge [3], the chemists are not clear what is and what is not a Maillard reaction. Frequently, articles include such statements as “The Maillard reaction is a very complex series of reactions”, which is a way of admitting the general perspective is far from clear. As said in the Maillard Challenge [3], the term “Maillard reaction” should be used to refer to interactions between an amino group and anα-hydroxy carbonyl moiety of a reducing sugar, which produces Amadori or Heyn’s products, depending on the particular sugar (aldose, ketose) [4–6]. A cascade of reactions follows, including many that have been studied outside the food context of Maillard reactions (thermolysis, oxidation, hydrolysis, reduction, aldol condensation, etc.), and the issue is whether such reactions should be included in the “Maillard reaction”. Of course, we could consider whether Maillard reactions include all these reactions, but it would result in a very complex system. It has been proposed that the Maillard reaction should be classified into its early, advanced, and final stages [7], but this proposal was recognized as simplistic. Later [8], it was proposed that the propagation of the Maillard reaction could be described by the formation and interaction of socalled “chemical pools” generated from specific precursors. Intermediates produced during the initial stage of the Maillard reaction arise from three well defined principal precursors: sugars (S), amino acids (A), and Amadori or Heyn’s products (D). The nature and relative ratio of the principal precursors, which constitute the parent mixture (A + S + D) determines the pathway of the Maillard reaction for particular conditions. The proposal to use the term “fragmentation pools” is not convenient, because what was called “advanced Maillard reactions” involved not only fragmentations but also condensations. However, such a proposal has the disadvantage that “Maillard reactions” would include chemical reactions for which there is no Schiff base, for example caramelization [9, 10], hence the proposal is to restrict the Maillard reaction solely to the first step of Schiff base formation. Indeed, the situation is the same as for the discovery of chlorophylls, when the French chemist Joseph-Bienaime Caventou (1795–1877) proposed the name “chlorophylle” for what cooks had, for centuries, called “spinach green” [11, 12]. Caventou only wanted to conduct a new This article is the solution to the Analytical Challenge to be found at Doi: 10.1007/s00216-015-8714-2