BROWNING OF SUGAR SOLUTIONS. IV. THE EFFECT OF PH ON THE VOLATILE PRODUCTS OF REDUCING SUGARS^a

Abstract

The principal steam volatile carbonyl compounds obtained from the alkaline decomposition of reducing sugars are generally considered to be methylglyoxal and acetol. These compounds have also been suggested as browning intermediates (22,23). It is still doubtful, however, as to which of these two compounds represents the major product formed in the reaction. Fernbach and Schoen (7), Fischler (8,9), E vans (6), and Enders (3, 4, 5) have implicated methylglyoxal on the basis of the isolation of its phenylosazone. However, Sattler and Zerban (16) have questioned the use of this technique as positive proof of the presence of methylglyoxal since methylglyoxalosazone can also be formed from acetol. Baudische and Deuel (1) by means of a specific reaction of acetol with o-a~~linohenzaldel~~~le have indicated that it is acetol and not methylglyoxal which is produced in the distillation of glucose from weakly alkaline solution. Similarly, Nodzu et al (12,13) based on the differential solubility of the semi-carbazone of acetol and methylglyoxal, also report the production of acetol but not methylglyoxal from several reducing sugars in mildly alkaline solutions. Prey and his co-workers (14, 15) using paper chromatography were able to demonstrate the formation of both acetol and methylglyoxal in alkaline solutions of glucose. dihydroxyacetone and glyceraldehyde. Similarly, Sattler and Zerban (17) have isolated acetol and a relatively lesser amount of methylglyosal through solvent extraction of heated aqueous fructose solution. During our investigation on color development in maple sirup, which is thought to occur through an alkaline degradation of the hexose constituents of the sap, several low molecular weight carbonyl compounds have been isolated as their dinitrophenyl-bis-hydrazones (21). In an attempt to clarify further the nature of these compounds and their role in the mechanism of color and flavor development in the sirup, the authors have for some time heen conducting experiments with model systems of dilute sugar solutions. In these preliminary studies it was observed that under varied experimental conditions, particularly of pH, the volatile constituents obtained from the sugars varied in both the nature of the compounds and in the amounts produced. This suggested that the pH of the reaction could explain why either acetol or methylglyoxal have been identified as the primary steam volatile products of the degradation. To clarify the extent to which these

BROWNING OF SUGAR SOLUTIONS. V. EFFECT OF PH ON THE BROWNING OF TRIOSESa,b

“…This formed constituent is no doubt methylglyoxal since it has been shown by earlier work in this laboratory (8) that the formation of methylglyoxal from these two triose sugars is increasingly favored as the pH is decreased to 4. Previous work here (8) has also shown that as the pH of solutions of these two sugars is decreased below 7 little or no acetol is formed. This indicates that methylglyoxal is being formed and that it is involved in the acid browning of dihydroxyacetone and of glyceraldehyde.…”

“…(ll) and Thornton and Speck (16) that in acid solution methylglyoxal is formed from dihydroxyacetone and by Nodzu et al (11) and Prey et al (13) that acetol, and by Bauer and Teed (2) and Weygand (17) that triose-reductone are formed in alkaline solutions. These findings together with work done at this laboratory (8) Laboratories as a dark brown amorphorous material which was purified by sublimation under vacuum (2 mm) at 40" C. The white sublimate was stored under nitrogen.…”

Factors affecting the formation of pyrazine compounds in sugar-amine reactions

“…Presently it is not known if the condensation and subsequent reduction of acetoin with ammonia forming tetramethylpyrazine is enzymatic. Lento et al (1960a) studied the formation of some 3-carbon carbonyl compounds from glucose and fructose heated in buffer solutions. It was suggested (Lento et al, 1960b) that acetol (hydroxyacetone) might be an important intermediate in the browning reaction at high pH levels.…”

Maillard Reaction Products Formed fromd-Glucose and Glycine and the Formation Mechanisms of Amides as Major Components

“…This result suggests that oxidative cleavage of glucose occurs in the early stage of the bre>wning reaction. Lento et al 10 ) have reported that diacetyl was produced from glucose in strong alkaline boiling solutions, but not formed from glucose at pH 8"" 9. In the present investigation, it became clear that larger amounts of diacetyl were formed as headspace volatiles in neutral pH ranges of the amino-carbonyl reaction.…”