engleski

Microwave-assisted extraction of polyphenols from coffee (green and roasted) and its by-products (silver skin and spent coffee ground)

Coffee is the most important food commodity worldwide. Its economic importance is mainly due to an infusion prepared from the roasted and grounded coffee beans. Concerning the large production of coffee, as well as coffee consumption, the significant amounts of by-products are generated. In many cases the wasted fractions of coffees, such as silver skin (SS) and spent coffee ground (SCG) are not properly handled, and thus presented the highly pollutant biomasses for the environment. On the other hand, their ample chemical composition made both substrates as valuable resources for isolation of various compounds. In that connection, the present work shows the possibility of exploiting them as low-cost sources for polyphenols isolation. The SS and SCG obtained by roasting of green coffee, and by the treatment of roasted and grounded coffee powder with hot water to obtain brew were extracted by microwave (MAE), at T = 50 and 70 °C, t = 5 and 15 min, and  (ethanol) = 50 and 70 %. With the aim to evaluate the recovery of polyphenols from SS and SCG, the extraction was also done on green and roasted coffees. The results obtained by UV/Vis spectrophotometry show that mass fractions of phenols decreased from roasted (57.79-70.98 mg/g) and green (48.48-56.64 mg/g) coffees to SCG (8.63-12.95 mg/kg) and SS (7.23-9.32 mg/g) residues, depending on used extraction parameters. The extraction done by refluxing for 2 h revealed the similar trend as MAE, i.e. espresso coffee (69.1-71.1 mg/g) > green coffee (46.8-47.5 mg/g) > SS (11.7-13.1 mg/g) > SCG (10.8-12.1 mg/g). Although the lower quantities of phenols were found in SS and SCG in comparison with espresso and green coffees, these by-products are still valuable, considering the facts that they are natural, inexpensive sources for their isolation. In addition, the results showed that not only the time, but also the temperature and solvent influence on phenols yields from these biomasses. For instance, the 50 °C and 50 % ethanol, and 70 °C and 70 % ethanol provided the best recovery of phenols from them. Thus, using mentioned parameters with minimal expenditure of time (5 min) it is possible to provides numerous extractions from SS and SCG by-products.

coffee by-products ; silver skin ; spent coffee grounds ; microwave-assisted extraction ; polyphenols ; UV/Vis spectrophotometry

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