Different types of model melanoidins were thermally degraded, with subsequent identification of the volatiles produced, to obtain and compare the thermal degradation profile of various melanoidins. At first, the volatiles produced from heated glucose/glycine standard melanoidins were compared with glucose/glutamic acid and L-(+)-ascorbic acid/glycine standard melanoidins. In the headspace of heated glucose/glycine melanoidins, mainly furans, were detected, accompanied by carbonyl compounds, pyrroles, pyrazines, pyridines, and some oxazoles. Heating of L-(+)-ascorbic acid/glycine melanoidins resulted in relatively more N-heterocycles, while from glucose/glutamic acid melanoidins no N-heterocycles were formed. In a second part, a chemical treatment was applied to glucose/glycine melanoidins prior to the thermal degradation. Acid hydrolysis was performed to cleave glycosidically linked sugar moieties from the melanoidin skeleton. Nonsoluble glucose/glycine melanoidins were also subjected to an oxidation. The results indicate that the thermal degradation profile is a useful tool in the characterization of different types of melanoidins.

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Nondialyzable and water-insoluble melanoidins, isolated from a glucose/glycine model reaction mixture, which was prepared in a standardized way according to the guidelines of the COST Action 919, were heated at different temperatures ranging from 100 to 300 °C. Among the volatile compounds, which were analyzed by SPME and GC-MS, pyrazines, pyridines, pyrroles, and furans were detected. In general, total amounts of volatile compounds increased with the temperature. When water-insoluble melanoidins were heated, especially at higher temperatures, this resulted in a higher diversity of isolated compounds. For furans, pyrroles, pyrazines, and carbonyl compounds a maximum was observed in the case of high molecular weight melanoidins around 200-220 °C. Pyridines and total oxazoles, however, were generated in higher yields with increasing temperatures. These results demonstrate the possibility of producing some flavor-significant volatiles from heated standard melanoidins at temperatures relevant to food preparation and contribute to the flavor aspects originating from melanoidins.

High-molecular-weight (HMW) water-soluble melanoidins were prepared from model systems of L-(+)-ascorbic acid-glycine, L-(+)-ascorbic acid-lysine, L-(+)-ascorbic acid-glutamic acid, and glucose-glycine using a very recently approved standard protocol. The amount of HMW water-soluble melanoidins prepared from L-(+)-ascorbic acid was over 5-15 times higher than the amount obtained from glucose. The study of the release of a model flavor compound, namely isoamyl acetate, from melanoidins by solid-phase microextraction (SPME) showed that SPME is a suitable technique for the analysis of flavor release from melanoidin-containing solutions. From the studies on the retention capacity of the melanoidins toward isoamyl acetate, an increased release of the flavor compound was observed from the melanoidins prepared from the L-(+)-ascorbic acid-glycine model system, whereas the opposite effect was observed from the melanoidins prepared from the L-(+)-ascorbic acid-lysine/glutamic acid model systems. The melanoidins prepared from the glucose-glycine model system had the same effect as the melanoidins prepared from the L-(+)-ascorbic acid-glycine model system.

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The production of 6-acetyl-1,2,3,4-tetrahydropyridine (ATHP), an important Maillard flavor component, in the reaction of L-(-)-proline and 1,3-dihydroxyacetone was investigated as a function of different reaction conditions. The two major side products from the reaction were identified as 5-acetyl-6-methyl-2,3-dihydro-1H-pyrrolizine and 5-acetyl-6-hydroxymethyl-2,3-dihydro-1H-pyrrolizine, the last one being a new compound described here for the first time. A maximum yield of ATHP of 2.7 mol % from L-(-)-proline and 1,3-dihydroxyacetone was noted at 130 degrees C in the presence of 2 equiv of sodium bisulfite. The role of sodium bisulfite as a reducing species, and as a stabilizing agent for 6-acetyl-1,2,3,4-tetrahydropyridine, was clarified. In view of the new data obtained, the hypothesized mechanism of formation of 6-acetyl-1,2,3,4-tetrahydropyridine was confirmed, and the reaction mechanisms leading to 2,3-dihydro-1H-pyrrolizines were reconsidered.

In this study, different amounts (from 2% to 4.5%) of dietary fiber-rich cranberry pomace (CP) were added to yogurt before or after fermentation to increase dietary fiber content without changing the textural properties of the product. The addition of CP reduced whey loss, improved the firmness and viscosity, increased the total phenol compound content and the antioxidant capacity values (DPPH•, ABTS, and ORAC) of the yogurt in a dose-dependent manner, and had no significant effect on the viability of the yogurt culture bacteria. For all CP-supplemented yogurt samples, the bioaccessibility index of the polyphenols after in vitro intestinal phase digestion was approximately 90%. However, yogurt with CP added before fermentation exhibited a significantly (p < 0.05) lower degree of protein hydrolysis post-gastric and post-intestinal than the yogurt with CP added after fermentation. Yogurt supplemented with 4.5% CP could be considered a good antioxidant dairy product and a good source of dietary fiber.

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