Effect of Fermentation Time on Pyrazine Concentration of Thai Forasero Beans

Abstract

A study on the effect of fermentation time on pyrazine concentration of Thai Forastero cocoa beans was carried out. Samples were taken during 4, 5, 6 and 7 days of fermentation and then dried and roasted at 150^oC for 15 min. Fructose was the major sugar in cocoa beans followed by glucose and sucrose. Aspartic acid, glutamine, leucine, and arginine were the major amino acids in Thai cocoa beans. As fermentation progressed all sugars and amino acids decreased. Three major methyl pyrazines, i.e. dimethylpyrazine, trimethylpyrazine and tetramethylpyrazine were found in Thai cocoa beans after roasting. The concentrations of tetramethylpyrazine was the highest (89.95 µg/100g ) in the samples that had been fermented for 5 days. Five-day fermented beans had the strongest cocoa aroma that agreed with the highest in pyrazine concentration of the sample. Sensory score was well correlated with the pyrazine concentration but was not strongly correlated with the flavor precursor concentrations. It is indicated that fermentation for 5 days is the most appropriate for Thai Forastero cocoa beans to produce the highest pyrazine concentration.