Determination of Chlorogenic Acids with Lactones in Roasted Coffee

An HPLC method has been developed which allowed the determination of mono- and dicaffeoylquinic acids (CQA and di-CQA), corresponding lactones (CQL) and feruloylquinic acids (FQA) in roasted coffee within one chromatographic run. The elution order was verified by isolation of the individual compounds by preparative HPLC, chromatography of the fractions on the analytical HPLC system, NMR spectroscopy and thermospray LC-MS. At least 15 additional minor compounds had the spectra of hydroxycinnamic acids, some of them only occurring in roasted coffee. Caffeoyltryptophan, which has been identified some time ago by another working group could also be separated with this system. The average contents in commercial roasted coffee samples (n=12) were: 3-CQA, 5·0 g kg−1; 4-CQA, 6·2 g kg−1; 5-CQA, 11·4 g kg−1; 4-FQA, 0·7 g kg−1; 5-FQA, 1·4 g kg−1; 3-CQL, 2·1 g kg−1; 4-CQL, 1·0 g kg−1; 3,4-di-CQA, 0·7 g kg−1; 3,5-di-CQA, 0·4 g kg−1 and 4,5-di-CQA, 0·8 g kg−1 dry matter. There were only small differences between the different brands. Two series of samples with different degrees of roast produced from the same green coffee have also been analysed. One series was steam treated before roasting (a process which is commercially used to improve digestibility). Only in the initial stages of roasting (light roast) could a difference in the contents of the acids between both series be observed. Keeping coffee brews at an elevated temperature (4 h at 80°C) reduced the amounts of CQL to 60% of the initial value. The contents of 3-CQA and 4-CQA increased, whilst that of 5-CQA decreased. The overall contents of CQA decreased.