Sara I.F.S Martins

A review of Maillard reaction in food and implications to kinetic modelling

This paper reviews some of the research designed to lead to an increased understanding of the chemistry of the Maillard reaction, based on recent developments, and its influence on food properties like colour, flavour and nutritional value. A critical analysis is given on how quality attributes associated with Maillard reaction can be predicted and controlled by kinetic modelling. Multiresponse modelling (taking more than one reactant and product into consideration in the modelling process) is a powerful tool to model complicated consecutive and parallel reactions, like the Maillard reaction. Such a multiresponse approach provides a major guidance in understanding the reaction mechanism. An illustrative example is given.

Melanoidins extinction coefficient in the glucose/glycine Maillard reaction

Melanoidins (brown, nitrogenous polymers and co-polymers) are the final products of the Maillard reaction. The glucose/glycine melanoidins extinction coefficient was determined using C-14-labelled glucose at three different reaction conditions. The absorbance was measured at different wavelengths (420, 450, 470 and 490 nm) and the extinction coefficient determined for each. The value of the extinction coefficient can be used to recalculate browning, measured as absorbance units, into melanoidins concentration in terms of sugar molecules incorporated. The amount of C-14-labelled sugar molecules was estimated in melanoidins separated via dialysis with a cut-off value of 3500 Da. These melanoidins only represented approximate to12% of the total colour formed. The extinction coefficient of the melanoidins remained constant during the observation period. At 470 nm, values of 0.65 (+/-0.02) 1 mmol(-1) cm(-1); 0.66 (+/-0.02) 1 mmol(-1) cm(-1) and 0.62 (+/-0.05) 1 mmol(-1) cm(-1), were obtained at 120 degreesC pH 6.8, 100 degreesC pH 6.8 and 100 degreesC pH 5.5, respectively. The difference is not significant. The extinction coefficient appeared to not to vary within the pH and temperature range studied. From the elemental analysis, the nondialysable melanoidins elementary composition seemed to be influenced by the reaction conditions, which was supposed to be related to the presence of side-chains on the melanoidin backbone. A trend was observed in the melanoidins C/N ratio: it decreased with increasing reaction pH as well as it changed to a lower level, of about 8, as the extent of browning increased

Kinetic modelling of Amadori N-(1-deoxy-D-fructos-1-yl)-glycine degradation pathways. Part I - Reaction mechanism

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 degrees C 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 alpha-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 degrees C 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.

Kinetic modelling of Amadori N-(1-deoxy-d-fructos-1-yl)-glycine degradation pathways. Part II—Kinetic analysis

A kinetic model for N-(1-deoxy-D-fructos-1-yl)-glycine (DFG) thermal decomposition was proposed. Two temperatures (100 and 120 degrees C) and two pHs (5.5 and 6.8) were studied. The measured responses were DFG, 3-deoxyosone, 1-deoxyosone, methylglyoxal, acetic acid, formic acid, glucose, fructose, mannose and melanoidins. For each system the model parameters, the rate constants, were estimated by non-linear regression, via multiresponse modelling. The determinant criterion was used as the statistical fit criterion. Model discrimination was performed by both chemical insight and statistical tests (Posterior Probability and Akaike criterion). Kinetic analysis showed that at lower pH DFG 1,2-enolization is favoured whereas with increasing pH 2,3-enolization becomes a more relevant degradation pathway. The lower amount observed of 1-DG is related with its high reactivity. It was shown that acetic acid, a main degradation product from DFG, was mainly formed through 1-DG degradation. Also from the estimated parameters 3-DG was found to be the main precursor in carbohydrate fragments formation, responsible for colour formation. Some indication was given that as the reaction proceeded other compounds besides DFG become reactants themselves with the formation among others of methylglyoxal. The multiresponse kinetic analysis was shown to be both helpful in deriving relevant kinetic parameters as well as in obtaining insight into the reaction mechanism.

Fate of glycine in the glucose–glycine reaction: a kinetic analysis

Abstract The behaviour of glycine was studied in its reaction with glucose at pH 6.8 between 80 and 130 °C. Glucose reacted more strongly than glycine, which was due to two phenomena: (i) besides its participation in the Maillard reaction, glucose also isomerizes into fructose and (ii) intact glycine is released from the initial Maillard condensation products in the intermediate phase of the reaction. From 80 to 100 °C, the loss of glycine could be completely accounted for in the Amadori product (ARP) and the melanoidins. At higher temperatures, a small loss occurred (10–20% of the initial glycine concentration) probably due to formation of Strecker reaction products. The behaviour of glycine is such that the kinetics of its decrease in the Maillard reaction cannot be taken as a measure for the progress of the Maillard reaction.

Understanding fat, proteins and saliva impact on aroma release from flavoured ice creams

The release profile of fourteen aroma compounds was studied in ice cream samples varying in fat and protein, both in level and type. In vitro aroma release was monitored by solid phase micro-extraction gas chromatography using an innovative saliva reactor, which imitated human chewing under temperature control. The results showed that the effect of the fat type on aroma release was smaller than that of fat level. Ice creams with low fat level released more hydrophobic aroma compounds than ice creams with high fat level. At low fat level more aroma compounds were released from ice creams with lower protein content. At high fat level a small increase of aroma release was observed by the addition of saliva, which was explained by a salting out effect, due to the presence of proteins and salts in the saliva. These findings confirmed that the interactions between salivary proteins and aroma compounds occurring in aqueous solutions are not observed in emulsions.