Extraction, identification and quantification of polyphenols from spent coffee grounds by chromatographic methods and...

A solid-liquid extraction method using ethanol-water mixtures was combined with cLC-DAD, LC-MS/MS and chemometric analyses for establishing the optimum extraction conditions of valuable polyphenols from spent coffee grounds. Chlorogenic and p-coumaric acids were the most abundant polyphenols found, ranging from 0.02 to 4.8 mg g^-1 and 0.173-0.50 mg g^-1, respectively. In addition, total polyphenol content (9-29 mg GAE g^-1 DW), total flavonoid content (11-27 mg QE g^-1 DW), total antioxidant activity (0.3-7 mg GAE g^-1 DW) and free radical scavenging ability (DPPH assay, 64-927 µg extract g^-1 at EC₅₀) of obtained extracts were determined. Response surface methodology allowed obtaining predictive models for the extraction of each individual polyphenol. On the other hand, multifactorial ANOVA was used to establish differences between coffee and spent coffee ground extracts. Principal component analysis was also employed to relate antioxidant activities, total polyphenol and total flavonoid contents with both the polyphenols extracted and the residue coffee type. The overall results suggested that spent coffee grounds could be reused as a promising, inexpensive and natural source of bioactive polyphenols with potential industrial applications, thus minimizing the waste disposal and environmental impact.