Investigation of volatile compounds of Liberica coffee beans fermented at varying degrees of roasting

Liberica coffee (Coffea liberica Bull ex Hiern) has gained worldwide popularity, because it has a unique taste and aroma, and it is able to adapt to peatlands and is more tolerant of disease. Previous studies suggested that fermentation with hydrolytic bacteria could improve flavors, mostly determined by volatile compounds by the roasting process. However, studies about the volatile compounds and their roles in the taste and aroma of this coffee are still limited. This study aimed to investigate volatile compounds from fermented Liberica coffee beans roasted at light roast (150-160°C, 2.2 Mbar, 12 mins); medium roast (175-185°C, 2.2 Mbar, 7.30 mins); and dark roast (200-220°C, 2.2 Mbar, 10 mins). Samples were collected from various fermentation times 0, 4, 8, and 12 hrs and dried. Green beans with a moisture content of 12% were roasted in 3 roast stages. In this work, the extraction of volatile coffee compounds was performed using solid phase microextraction (SPME) and subsequently analyzed by gas chromatography-mass spectrometry (GC-MS). To determine the significance of fermentation time and degree of coffee roasting in the area, a two-way univariate analysis of variance (ANOVA) test was used, followed by a Tukey's honest significant difference (HSD) test with a statistical significance level of p<0.05. The results showed that a total of 59 of the 130 volatile compounds had a significant difference at different roasting degrees to the area of compounds with a statistical significance level of p<0.05. Those compounds consisted of 5 aldehydes, 18 furans, 4 ketones, 9 phenols, 13 pyrazines, 5 pyridines and 5 pyrroles.