The chemical composition of exhausted coffee waste

Abstract

The chemical composition of exhausted coffee waste generated in a soluble coffee industry was investigated. The chemical characterization included elemental analysis, mineral composition and ash content, summative composition; acidic functional groups, lipophilic extractives, total polyphenols, condensed tannins determination and FTIR analysis. The spent coffee samples showed high carbon (>58%), low nitrogen (<2%), and low ash (<1%) contents and low polarity coefficient (O+N)/C (<0.5). The summative composition reveals that extractives are the main components of exhausted coffee wastes (54%). This percentage includes lipophilic fractions (24%), ethanol and water soluble compounds (5%), and compounds solubilized in 1% NaOH (26%). Lignin and polysaccharides were found in a similar proportion between 20 and 26%. The GC analysis of monosaccharide showed about 60% glucose and 40% mannose. The main components in the lipophilic extractives are free fatty acids (>60%) of which more than 30% was identified to be n-hexadecanoic acid. Total polyphenols and tannins represent <6% and <4% of the exhausted coffee wastes, respectively. Assignments of the bands of the obtained FTIR spectra confirm the presence of lipids, polysaccharides and chlorogenic acid. Exhausted coffee wastes showed characteristics for various potential applications such as biodiesel production, as a source of antioxidants and as a biosorbent of hydrophobic pollutants.