Non‐enzymic browning: The role of unsaturated carbonyl compounds as intermediates and of so₂ as an inhibitor of browning

Abstract

The browning potentialities of a number of carbonyl compounds has been examined. From the results it is clear that most rapid browning with a reactive nitrogen function occurs with straight chain NP-unsaturated aldehydes. When the conjugated unsaturation is within a ring structure, as in the furfurals, chromophore development is slower. When the unsaturated centre is substitated, the browning rate is much reduced. Saturated carbonyl compounds are of relatively low browning potential.The retardation in the browning of carbonyl/amino systems caused by sulphites is due to combination of the sulphite both with the carbonyl group and with unsaturated centres. The latter reaction probably occurs by an ionic mechanism in the case of aa-unsaturated carbonyl compounds.Inactivation of sulphites as browning reaction inhibitors occurs through combination a t sites of unsaturation to form sulphonates, which do not readily yield SO, on acid hydrolysis by the Monier-Williams technique. This explains the loss of sulphites observed on storage of foodstuffs, and the observations that sulphite loss is not matched by concomitant equivalent sulphate development or loss of volatile sulphur, or by the formation of free sulphur. IntroductionIn a previous publication] it was reported that a number of carbonyl compounds, many of them of a conjugated unsaturated nature, had been isolated from a glucose/glycine model system. At the time the work was in progress, a number of papers were published2-* which appeared to confirm our view that browning in foodstuffs was a reaction which involved a number of unsaturated carbonyl compounds. The whole group of reactions, known as non-enzymic browning, probably commences with carbonyl-amino type group reactions ; previous work in the browning field has bee;i reviewed. [5][6][7][8] The most effective agents in the retardation of non-enzymic browning are both reducing agents and carbonyl-group reactants, and of these sulphur dioxide and the salts of sulphurous acid are widely used in the food industry.The effect of sulphites is but little understood, and in the past has often been ascribed to combination with aldose carbonyl groups, or to reaction with ' active aldehydic ' intermediate~.~> lo Recently, work in these laboratories has indicated that sulphites may act at more than one point in the chain of reactions ; where sugars are the main source of the carbonylic groups required for the carbonyl/amino reaction, one of the earliest effects of sulphite appears to be on the sugar stability,]] which conclusion appears to be supported by findings in related fields.12, l3 In late stages of the reaction where sugars are present, and also in the absence of sugars, the effect of sulphites seems to be connected with the development of unsaturated, carbonyl-derived chromophores. l4 Leal5 and Tappel,16 for example, mention the importance of carbonyl/amino reactions due to oxidised fat, which reactions also appear to occur in ph.osphatide model systems.llc Ingles and colleagues, from studies on non-enzymic browni...

Mutagen formation during commercial processing of foods.

“…They also suggest that Maillard type reactions may be involved in mutagen formation and browning reaction inhibitors might diminish the levels of mutagens. As seen in Table 8, the introduction of NaBH4 or NaHSO3, both of which interact with carbonyl groups to block browning reactions (44,45), eliminated mutagen formation in the model systems, thus supporting the above conjecture.…”

Effect of bottle colour and storage conditions on browning of orange wine

“…The amount of ascorbic acid in this study decreased by 50% during storage time as reported in other studies. The formation of browning depends on the degradation of ascorbic acid leading to the formation of carbonyl compounds [21][22][23].…”

The Rate and Mechanism of Long Chain 2,3-Dialkyl Acroleins Formation in Meat by Heat Treatment

“…This observation suggested that DAA ) VIC reaction occurred in meat by heat treatment at higher temperature but the rate of its reaction was very slow. Burton et al 5 ) showed that a,,B-unsaturated straight chain aldehydes greatly accelerated by initial development of chromophores in foods, but this effect was not shown by the unsaturated aldehydes with alkyl substituent on the a-carbon atom (2,3-dialkyl acroleins). On the basis of these data, DAA seemed to be stable in meat.…”