Meat flavour generation in Maillard complex model systems

Meat flavour generation in Maillard complex model systems was studied. Mixtures of 3 amino acids and 2 sugars were studied at 3 concentration levels and 3 reaction times using a statistical factorial design. The selected systems tried to mimic the flavour composition in real food products containing both meat and tomato cooked together. Samples were compared by their thiol composition and sensorial profile. The used meat flavour generation marker was 2-methyl-3-furanthiol (MFT). It was observed that MFT formation was well correlated with cysteine and xylose as starting material as well as with the meaty sensory attribute. Synergetic effects seem to occur between glutamic acid and cysteine. In the presence of glutamic acid the sensorial profile changed from burnt, roasted meat to boiled meat, bouillon-like. Also the reaction kinetics of MFT generation changed in the presence of glutamic acid. We strongly believe that to study model systems with increased complexity will give results which can more reliably be translated to real food products. Introduction The formation of thiols, related to meat flavour, during the Maillard reaction has been known for decades (1). Besides thiamine, sulphur containing amino acids, such as cysteine, are known to be indispensable reaction precursors. In the presence of ribose or its less expensive isomer xylose, they participate in the Maillard reaction and Strecker degradation to form sulphur-containing compounds characteristic of meat odour (Figure 1). A number of which have been identified and reported in literature. Up-to-date, most studies focused on simple model systems, using only one sugar and one amino acid. Often those results are difficult to translate into real food products. The complex composition of real food products is expected to have a big impact on the reaction kinetics of the generated flavour compounds as well as on the final sensory profile (2). Farmer et al. (3) reported that the cysteine/ribose/lecithin reaction mixture had a much more pronounced “meaty, beefy” odour than a reaction mixture containing cysteine and ribose only. The aim of the present study was to better understand the impact of the system composition on the kinetics of known meat flavour generation markers. Also, to verify if the sensorial profile changed as a result. The selected systems’ composition tried to mimic meat flavour generation in real food products containing both meat and tomato cooked together. Experimental Meat flavour related complex model systems (more than one sugar and one amino acid) were studied using a statistical experimental design. Time and concentration Expression of Multidisciplinary Flavour Science 294 were the variable parameters, whereas pH and temperature were kept constant at 6 and 100°C, respectively, as shown in Table 1. The type of reactants was also a variable parameter, however in order to provide a minimum of meat flavour generation all systems had a minimum level of xylose and cysteine present. The studied systems were heated at 100°C in pyrophosphate buffer solution (50 mL, 0.2M, pH 6). D-Glucose (D-Glc), D-Xylose (D-Xyl), L-Cysteine (L-Cys), L-Glutamic acid (L-Glu), L-Glycine (L-Gly), 2-methyl-3-furanthiol (MFT), furfurylthiol (FFT) and bis(2methyl-3-furanyl) disulfide (MFT-MFT) were purchased from Aldrich (Zwijndrecht, The Netherlands) and the respective stable-isotope labelled internal standard (labelling degree >98%) MFT* ([2H3] 2-methyl-3-furanthiol) and MFT*-MFT* ([2H6] bis(2-methyl-3-furanyl)disulphide) from AromaLAB AG (Munich, Germany). Prior to analysis by SPME GC-MS, 1% dithiothreitol (DTT) was added, enough to enable reducing conditions (reducing potential: -330 mM). Under these conditions the measured thiols were prevented from oxidation and/or liberated from already established sulphide bounds. Sensorial evaluation was done with an expert panel of 10 panellists. Common Flavour Language references were used. A standardised communication tool for sensory purposes developed by Unilever, International Flavour & Fragrances, Firmenich and Symrise. Figure 1. 2-Methyl-3-furanthiol (MFT), furfurylthiol (FFT) and bis(2-methyl-3-furanyl) disulphide (MFT-MFT), known meat aroma volatiles, formed by the reaction of cysteine with carbonyl compounds. Adapted from Mottram & Mottram (1). Table 1. Complex model systems composition (%) heated at 100°C, pH 6. Sample D-Xyl D-Glc L-Cys L-Gly L-Glu Time (h) A 3 0 0.05 1.5 1.5 3 B 0.05 3.6 0.75 0 0 0.5 C 0.05 3.6 0.05 1.5 0 3 D 3 0 0.75 1.5 1.5 1.75 E 0.05 3.6 0.05 0 1.5 0.5 F 3 3.6 0.05 1.5 0 0.5 G 0.05 0 0.75 0 0 1.75 H 3 0 0.75 1.5 0 3 Cysteine H 2 S NH3 CH 3 CHO S H O H O