Effects of urea, carnosine, DNA on volatile generation from Maillard reaction model system of ribose and cysteine

This thesis is composed of four chapters dedicated to meat flavor research. The first chapter is a literature review section covering aspects related to meat volatiles from their sources to their generation as well as factors influencing the aroma profile of meat volatile. The rest three chapters consist of three original studies investigating the effects of urea, carnosine and DNA on volatile generation from Maillard reaction of ribose and cysteine, respectively.; Urea, carnosine and DNA were added separately into the mixtures of cysteine and ribose, which were heated to the roasting temperature of 180°C for 2 hours at both pH 5 and 8.5. Volatiles identified from the reaction system of ribose and cysteine showed that sulfur-containing compounds such as thiophenes, thiazoles and thiophenethiols were the most abundant compounds. The addition of urea into tire reaction mixture caused the disappearance or reduction in content of some sulfur-containing compounds, but resulted in the generation of several important nitrogen-containing volatiles, like pyrazine, methylpyrazine, 2,5 (or 2,6)-dimethylpyrazine and other alkylpyrazines, which are known to elicit roast, nutty flavor notes. A plausible explanation for this phenomenon is that ammonia can be released from urea upon heating and the ammonia competes with hydrogen sulfide liberated from cysteine to react with other reaction precursors to produce nitrogen-containing compounds such as alkylpyrazines.; Carnosine and DNA both affected volatile formation from the reaction of ribose and cysteine in complex manners. They mitigated the sulfurous, meaty aroma by reducing the concentration of some well-known meat flavor compounds such as 2-methyl-3-furanthiol, 2-furfurylthiol, 2-methyl-3-thiophenethiol and their associated dimers as well as some thiophenes. On the other hand, like urea, they facilitated the generation of several important nitrogen-containing compounds such as pyrazine, methylpyrazine, dimethylpyrazine cyclopentapyrazine and thiazoles. In DNA involved thermal reactions, 2-furfuryl alcohol was the characteristic compound, which elicits a sugary aroma. It reacted with hydrogen sulfide to form 2-thiophenemethanol, and possibly it can also react with adenine to produce kinetin (N-furfuryladenine). The results suggested that carnosine and DNA act as limited nitrogenous sources to facilitate the formation of nitrogen containing compounds. This thesis work helps understanding the effects of these compounds on flavor formation during meat cookery.