Microwave-assisted extraction of chlorogenic acids from green coffee beans

Microwave-assisted extraction of chlorogenic acids from green coffee beans

Chlorogenic acid (5-O-caffeoyl-quinic acid), an ester of caffeicacid with quinic acid, has received considerable attention for its potential biological effects and wide distribution in nature (Clifford,

1999). It is one of the most abundant polyphenols in the human diet with coffee, fruits and vegetables as its major sources.Flowers and buds of Lonicera japonica Thunb, and the leaves of Eucommia ulmodies, which are rich in chlorogenic acids, are used in Chinese medicine. In the conventional method, chlorogenic acid is extracted from dried green coffee powder by refluxing with solvent, followed by filtration. However, this technique is time- as well as energy-consuming and laborious. Development of a new technique for the separation and purification of chlorogenic acid is thus of essential importance for the potential application and use of chlorogenic acid.

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The present study has focussed on microwave-assistedextraction of chlorogenic acid, caffeine and total polyphenols from green robusta cherry coffee. Aqueous and alcoholic (ethanol and methanol) extracts of green coffee bean, obtained by microwaveassisted extraction (MAE), were quantitatively analysed for chlorogenic acids, total yield of extracts, caffeine and total polyphenol content. The extracts were also evaluated for radical-scavenging activity. It was found that MAE at a temperature and wattage of 50 [1]C and 800 W, respectively, for the extraction period of 5 min, resulted in maximum yield of the above compounds. Under the optimum conditions of time (5 min), temperature (50 [1]C) and wattage (800 W), maximum chlorogenic acids (8.40%) and caffeine (7.25%) could be extracted and these concentrations were higher than those after the heat reflux extraction at 5 min and 50 ℃, respectively. The extracts contained chlorogenic acids in the range of 32–62% and caffeine in the range of 22–40%. MAE was compared with conventional methods of extraction and was efficient and reduced both time and solvent consumption. Also the extracts showed radical-scavenging activity of >75%, even at the concentration of 25 ppm. Microwaves are fast and reliable and the efficiency of extraction of phenolic compounds was improved in comparison with that of the heat reflux method. Water, a microwave-transparent solvent, proved to be the best choice to extract phenolic compounds from defatted and ground robusta cherry coffee when microwaves were used. This may be attributed to the better absorption of microwave energy, which increases temperature inside the plant cells, resulting in the breaking of cell walls and releasing compounds into the sur-rounding solvent. The MAE process can be predicted and controlled for industrial application with suitable arrangements for separation of active compounds. Hence, The MAE process can thus be predicted and controlled for industrial application.