Abstract: The main chemical composition of mildly, moderately, and heavily roasted coffee beans from three major coffeeproducing areas (Pu’er, Nujiang, and Dehong) in Yunnan province was analyzed and melanoidins were extracted from them for analysis by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) technique. Results showed that the contents of protein and fat in roasted coffee beans increased with the degree of roasting, and total amino acids decreased. The protein content of heavily roasted coffee beans from Pu’er was the highest (16.3 g/100 g), and the highest amino acid content (9.41%) was detected in raw coffee beans from Pu’er. On the other hand, moderately roasted coffee beans from Dehong had the highest crude fat content (13.85 g/100 g). The dominant minerals were K, Mg, P and Ca. The K content of heavily roasted coffee beans from Pu’er was the highest (2.2 g/100 g). The Py-GC-MS analysis indicated that the melanoidin composition of coffee beans varied significantly depending on geographic origin and roasting degree. However, there were some common characteristics. The contents of caffeine and acid were the highest, followed by esters, amines, phenols, pyrroles, furans, aldehydes, alcohols, ketones.

Key words: Yunnan coffee, principal component analysis, melanoidin, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS)