Coffee silver skin: waste or functional food?

Bioactive compounds are added-value products, giving a good reason to isolate them from the agroindustrial wastes. The latter could represent a “natural” sustainable source of many classes of substances such as, e.g., antioxidants, fibers and carbohydrates. Coffee silver skin (CS) is a waste of coffee production and, if not used, must be disposed of in the environment. However, CS recovery may be economically attractive as a possible source of food additives, supplements with high nutritional value and, after all the extractive possibilities, may be employed as biomass. The aim of the study was to investigate the lipophilic and hydrophilic composition of CS in order to isolate bioactive compounds and to formulate hypothesis of employment (e.g. functional foods, ingredient for cosmetics and animal feed). The humidity (about 4%), phenolic compounds (about 800 ppm), insoluble- (about 63.5%) and soluble-fiber (about 11.0%), caffeine and carbohydrates (about 1% each) were determined. For the extraction of liposoluble compounds different methods and solvents (n-hexane, chloroform and petroleum ether) were tested. The n-hexane resulted the most efficient, cheaper and sustainable. Free fatty acids (about 8%), free sterols (about 7%), diglycerides (about 8%), esterified sterols (about 12.0%) and triglycerides (about 65%) were components of the lipid fraction (about 3.3%). The total fatty acid methyl esters composition, determined by capillary gaschromatography, after transesterification of the lipid fraction, showed a higher saturated fat content (mainly palmitic acid, arachidic and stearic acid) than unsaturated (mainly linoleic acid).