Phenolic composition, caffeine content and antioxidant capacity of coffee silverskin

- Coffee silverskin contains a phenolic profile similar to that of coffee brews.
- Coffee silverskin shows an extremely high total antioxidant capacity and total polyphenol content.
- Coffee silverskin could represent an extremely interesting functional ingredient.

Coffea arabica silverskin (CSS), the inner fruit layer surrounding coffee beans, was analyzed for its (poly)phenolic and caffeine content by means of liquid chromatography-tandem mass spectrometry and evaluated for its antioxidant properties by means of the Folin-Ciocalteu and FRAP methods. The most abundant quantified phenolics were caffeoylquinic acids, with the 5- and 3-isomers being the most relevant (199 mg/100 g and 148 mg/100 g, respectively). The three caffeoylquinic acid isomers reached a total concentration of 432 mg/100 g, corresponding to 74% of the total chlorogenic acids detected in CSS. The level of the three feruloylquinic acids detected was 143 mg/100 g, corresponding to 23%, and the two identified coumaroylquinic acids plus the two caffeoylquinic acid lactones were only marginally contributing to the final figure (only 3% of total hydroxycinnamates). No unconjugated phenolic acid was detected. Caffeine content in CSS was equal to 10 mg/g of product, 3.5 times lower than most coffee brews. The total antioxidant capacity (TAC) of CSS was 139 mmol Fe2 +/kg, a value similar to those of valuable sources of food antioxidants like dark chocolate, herbs and spices. Besides its potential as a food supplement, CSS may represent an innovative functional ingredient exploitable to increase the TAC of a wide range of food products.