Browning initial stage

The physical properties of the brown pigment have been described by numerous workers, but, as the properties depend to a considerable extent on the conditions under which the pigments were formed, uniformity is not readily obtained. The pigment isolated during the initial stages of the reaction, especially at low temperature, is water soluble and acidic to litmus. It is not precipitated in aqueous solution by mineral acids, alkalis, or salts. 

The mechanism proposed so far takes account of the induction period and initial stages of the reaction only, and it is difficult to see how it can account for the large amount of hydroperoxide decomposed by the sulfur compound. However, Tetralin hydroperoxide is decomposed catalytically by acids (5). Although in the absence of dilauryl thiodipropionate the decomposition of Tetralin hydroperoxide in the presence of acetic acid at 70 °C. was very slow, if the acid species is a much stronger acid than acetic—e.g., a sulfonic acid as seems likely from the nature of the products of the reaction, the rate of acid-induced decomposition may be comparable with the rate of decomposition by the sulfur compound. Some evidence that acid-induced decomposition does occur at some stage in the over-all reaction is found in the presence of an ortho substituted aromatic compound in the solid product of the reaction. The acid catalyzed decomposition of Tetralin hydroperoxide follows the path of Reaction 14 (5) to give y-(o-hydroxyphenyl)butyraldehyde. This forms a brown resin which is mainly the aldol of this aldehyde (cfthe resin obtained in this work). 

According to Hayashi and Namiki (1986), glyoxal and methylglyoxal (C.38) result from sugar fragmentation and are formed in the initial stages of browning. 

The initial stage of the Maillard browning is a condensation reaction between the carbonyl group of an aldose and the free amino group of an amino acid, to give an N-substituted aldosylamine. This reaction, which is initiated by an attack of the nucleophilic amino compound on the carbonyl carbon, is reversible and requires an acidic catalyst. The Schiff base is in equilibrium with the cyclic aldosylamine structure as shown in Figure 11.9 [170]. 

Soils of the brown podzolic group have been studied by Rolfe and Jeffries [1953] in central New York State. Here the mica weathers to give a 14 A mineral. Some chlorite appears in the initial stage of weathering. Hydrated mica is dominant at the surface, but decreases with... 

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