Martinus A.J.S. van Boekel

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.

A review on the beneficial aspects of food processing

The manuscript reviews beneficial aspects of food processing with main focus on cooking/heat treatment, including other food-processing techniques (e.g. fermentation). Benefits of thermal processing include inactivation of food-borne pathogens, natural toxins or other detrimental constituents, prolongation of shelf-life, improved digestibility and bioavailability of nutrients, improved palatability, taste, texture and flavour and enhanced functional properties, including augmented antioxidants and other defense reactivity or increased antimicrobial effectiveness. Thermal processing can bring some unintentional undesired consequences, such as losses of certain nutrients, formation of toxic compounds (acrylamide, furan or acrolein), or of compounds with negative effects on flavour perception, texture or colour. Heat treatment of foods needs to be optimized in order to promote beneficial effects and to counteract, to the best possible, undesired effects. This may be achieved more effectively/sustainably by consistent fine-tuning of technological processes rather than within ordinary household cooking conditions. The most important identified points for further study are information on processed foods to be considered in epidemiological work, databases should be built to estimate the intake of compounds from processed foods, translation of in-vitro results to in-vivo relevance for human health should be worked on, thermal and non-thermal processes should be optimized by application of kinetic principles.

Extraction and characterisation of protein fractions from five insect species

Tenebrio molitor, Zophobas morio, Alphitobius diaperinus, Acheta domesticus and Blaptica dubia were evaluated for their potential as a future protein source. Crude protein content ranged from 19% to 22% (Dumas analysis). Essential amino acid levels in all insect species were comparable with soybean proteins, but lower than for casein. After aqueous extraction, next to a fat fraction, a supernatant, pellet, and residue were obtained, containing 17-23%, 33-39%, 31-47% of total protein, respectively. At 3% (w/v), supernatant fractions did not form stable foams and gels at pH 3, 5, 7, and 10, except for gelation for A. domesticus at pH 7. At 30% w/v, gels at pH 7 and pH 10 were formed, but not at pH 3 and pH 5. In conclusion, the insect species studied have potential to be used in foods due to: (1) absolute protein levels; (2) protein quality; (3) ability to form gels.

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

Incorporation of Chlorogenic Acids in Coffee Brew Melanoidins

The incorporation of chlorogenic acids (CGAs) and their subunits quinic and caffeic acids (QA and CA) in coffee brew melanoidins was studied. Fractions with different molecular weights, ionic charges, and ethanol solubilities were isolated from coffee brew. Fractions were saponified, and the released QA and CA were quantified. For all melanoidin fractions, it was found that more QA than CA was released. QA levels correlated with melanoidin levels, indicating that QA is incorporated in melanoidins. The QA level was correlated with increasing ionic charge of the melanoidin populations, suggesting that QA may contribute to the negative charge and consequently is, most likely, not linked via its carboxyl group. The QA level correlated with the phenolic acid group level, as determined by Folin-Ciocalteu, indicating that QA was incorporated to a similar extent as the polyphenolic moiety from CGA. The QA and CA released from brew fractions by enzymes confirmed the incorporation of intact CGAs. Intact CGAs are proposed to be incorporated in melanoidins upon roasting via CA through mainly nonester linkages. This complex can be written as Mel=CA-QA, in which Mel represents the melanoidin backbone, =CA represents CA nonester-linked to the melanoidin backbone, and -QA represents QA ester-linked to CA. Additionally, a total of 12% of QA was identified in coffee brew, whereas only 6% was reported in the literature so far. The relevance of the additional QA on coffee brew stability is discussed.

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.

Low Molecular Weight Melanoidins in Coffee Brew

Analysis of low molecular weight (LMw) coffee brew melanoidins is challenging due to the presence of many non-melanoidin components that complicate analysis. This study focused on the isolation of LMw coffee brew melanoidins by separation of melanoidins from non-melanoidin components that are present in LMw coffee brew material. LMw coffee fractions differing in polarity were obtained by reversed-phase solid phase extraction and their melanoidin, sugar, nitrogen, caffeine, trigonelline, 5-caffeoylquinic acid, quinic acid, caffeic acid, and phenolic groups contents were determined. The sugar composition, the charge properties, and the absorbance at various wavelengths were investigated as well. The majority of the LMw melanoidins were found to have an apolar character, whereas most non-melanoidins have a polar character. The three isolated melanoidin-rich fractions represented 56% of the LMw coffee melanoidins and were free from non-melanoidin components. Spectroscopic analysis revealed that the melanoidins isolated showed similar features as high molecular weight coffee melanoidins. All three melanoidin fractions contained approximately 3% nitrogen, indicating the presence of incorporated amino acids or proteins. Surprisingly, glucose was the main sugar present in these melanoidins, and it was reasoned that sucrose is the most likely source for this glucose within the melanoidin structure. It was also found that LMw melanoidins exposed a negative charge, and this negative charge was inversely proportional to the apolar character of the melanoidins. Phenolic group levels as high as 47% were found, which could be explained by the incorporation of chlorogenic acids in these melanoidins.

Electron spin resonance (ESR) studies on the formation of roasting-induced antioxidative structures in coffee brews at different degrees of roast.

The antioxidative properties of coffee brew fractions were studied using electron spin resonance spectroscopy using 2,2,6,6-tetramethyl-1-piperidin-1-oxyl (TEMPO) and Fremys salt (nitrosodisulfonate) as stabilized radicals. TEMPO was scavenged by antioxidants formed during roasting and not by chlorogenic acid, whereas Fremys salt was scavenged by all antioxidants tested including chlorogenic acid. The stabilized radical TEMPO allowed the exclusive measurement of roasting-induced antioxidants. The roasting-induced antioxidant activity of coffee brews increased with increasing degree of roast, and most of these antioxidants were formed during the initial roasting stage. The majority of these roasting-induced antioxidants were present in the high molecular weight fractions, indicating that the formation of these antioxidants preferably occurs at specific high molecular weight structures, likely being arabinogalactan and/or protein moieties which might be part of the melanoidin complex. It was found that chlorogenic acids most probably do not lose their antioxidant activity and phenolic characteristics upon incorporation in coffee melanoidins. The parameter fast reacting antioxidants (FRA) was introduced as an alternative for the antioxidative potential. FRA levels showed that coffee fractions rich in roasting-induced antioxidants exposed their antioxidant activity relatively slowly, which must be a consequence of its complex structure. Finally, the melanoidin content and the roasting-induced antioxidant activity showed a positive and linear correlation for the coffee brew fractions, showing that roasting-induced antioxidants are present within melanoidins. This is the first time that the formation of roasting-induced antioxidants could be directly correlated with the extent of Maillard reaction and melanoidin formation in a complex product such as coffee.

Formation of pyrazines and a novel pyrrole in Maillard model systems of 1,3-dihydroxyacetone and 2-oxopropanal.

Alkylpyrazines are a very important class of Maillard flavor compounds, but their mechanism of formation is complex and consists of different pathways. The model reaction of 20 different amino acids with 1,3-dihydroxyacetone, as a precursor of 2-oxopropanal, was studied by means of SPME-GC-MS to investigate the involvement of the amino acid side chain in the substitution pattern of the resulting pyrazines. 2,5-Dimethylpyrazine was quantitatively the most important pyrazine formed from all of the amino acids. The amino acid side chain is not involved in its formation. The substituents of other less abundant pyrazines resulted mainly from the incorporation of the Strecker aldehyde or aldol condensation products in the intermediate dihydropyrazine. The importance of different reaction mechanisms was evaluated, taking into account the pattern of pyrazines identified. In the solvent extracts of aqueous model reactions of 2-oxopropanal with amino acids, the main reaction product was not a pyrazine but a novel pyrrole. This pyrrole was identified as 2,5-diacetyl-3-methyl-1 H-pyrrole by means of spectral analysis, secured by chemical synthesis. A reaction mechanism for its formation was proposed and evaluated. The influence of various reaction conditions on the formation of 2,5-diacetyl-3-methyl-1 H-pyrrole and 2,5-dimethylpyrazine in the model reaction of alanine with 2-oxopropanal was studied. These results underscore the importance of the ratio of the different reagents and the presence of water in the resulting flavor formation in the Maillard reaction.

Kinetic Modeling of Reactions In Foods

The level of quality that food maintains as it travels down the production-to-consumption path is largely determined by the chemical, biochemical, physical, and microbiological changes that take place during its processing and storage. Kinetic Modeling of Reactions in Foods demonstrates how to effectively capture these changes in an integrative fashion using mathematical models. Thus, kinetic modeling of food changes creates the possibility to control and predict food quality from a technological point of view.