Bettina Cämmerer

Influence of roasting on the antioxidant activity and HMF formation of a cocoa bean model systems.

During the roasting of cocoa beans chemical reactions lead to the formation of Maillard reaction (MR) products and to the degradation of catechin-containing compounds, which are very abundant in these seeds. To study the modifications occurring during thermal treatment of fat and antioxidant rich foods, such as cocoa, a dry model system was set up and roasted at 180 degrees C for different times. The role played in the formation of MR products and in the antioxidant activity of the system by proteins, catechin, and cocoa butter was investigated by varying the model system formulation. Results showed that the antioxidant activity decreased during roasting, paralleling catechin concentration, thus suggesting that this compound is mainly responsible for the antioxidant activity of roasted cocoa beans. Model system browning was significantly higher in the presence of catechin, which contributed to the formation of water-insoluble melanoidins, which are mainly responsible for browning. HMF concentration was higher in casein-containing systems, and its formation was strongly inhibited in the presence of catechin. No effects related to the degree of lipid oxidation could be observed. Data from model systems obtained by replacing fat with water showed a much lower rate of MR development and catechin degradation but the same inhibitory effect of catechin on HMF formation.

Radical scavenging activity, anti-bacterial and mutagenic effects of Cocoa bean Maillard Reaction products with degree of roasting

Raw, pre-roasted and roasted Cocoa samples were separated into four different molecular weight fractions (> 30, 30-10, 10-5 and < 5 kDa) with ultrafiltration and tested for their antibacterial, mutagenic, as well as their radical-scavenging effects. Radical-scavenging effects were tested with electro paramagnetic resonance spectroscopy, anti-mutagenicity in the Salmonella microsome assay (with and without metabolic activation), and antibacterial effects by incubating the fractions with several strains of Bifidobacteria, Enterobacter and Escherichia, and observing their growth. The radical-scavenging activity and reducing substance concentrations increased, particularly in the 5-10-kDa roasted fraction. Chromaticity testing elucidated that the 10-5-kDa fraction was one of the darkest fractions. The Salmonella microsome assay showed neither mutagenic nor anti-mutagenic effects in any of the samples at any of the different concentrations applied when using TA98, TA100 and TA102. All fractions reduced the growth of pathogenic bacteria, in particular at the highest concentration of 100 microg/mL; however, the same trends were also observed for Bifidobacteria.

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.

Carbohydrate structures as part of the melanoidin skeleton

Abstract Chemical degradation reactions were used for structural investigation of melanoidins formed from oligomer and polymeric carbohydrates and amino acids. The released products were detected qualitatively and quantitatively by HPTLC and HPAEC/PAD. As result of hydrolysis of melanoidin models formed under water-free reaction conditions, a considerable amount of carbohydrate theoretically incorporated into the melanoidin was found as glucose. In comparison, hydrolysis of models formed under aqueous reaction conditions resulted in smaller glucose releases. Results indicated that oligo- and polysaccharides reacted in the Maillard reaction preferentially as complete molecules at the reducing end under water-free reaction conditions. Hydrothermolytic degradations and retro-aldol reactions of carbohydrates were favored under aqueous reaction conditions leading to the formation of more reactive monosaccharides. The results could be explained with the postulated melanoidin structure, which is mainly built up from amino-branched sugar degradation products.