Formation of aliphatic acids by carbohydrate degradation during roasting of coffee

A major fraction of the acidity generated on coffee roasting can be attributed to formation of the four aliphatic acids formic, acetic, glycolic and lactic. Addition of sucrose, glucose or fructose to green coffee beans gave, compared to untreated beans, significant increases in the yields of the four acids on subsequent roasting. In addition, model studies using these three carbohydrates confirmed sucrose as the principal green bean precursor of the acids. Arabinose, erythrose and 1,6-anhydroglucose were identified as reaction products of sucrose thermal degradation and also subsequently served as precursors for acid formation. Isotopic labelling experiments indicated that known degradation pathways could be used to explain the formation of the four aliphatic acids from sucrose.