Antioxidative polyphenolics obtained from spent coffee grounds by pressurized liquid extraction

Spent coffee grounds are produced in huge amount by cafeterias, restaurants and industries, which could be a good natural antioxidants resource. In this study, extraction conditions for total phenolics and caffeine from spent coffee grounds were optimized by pressurized liquid extraction (PLE) method with water and ethanol using statistical experimental design. The process was optimized by Plackett-Burman design to screen the most important variables for the extraction of total phenolics and caffeine firstly, and then central composite design (CCD) was performed to obtain the optimum conditions of the preferential factors for extraction. Temperature and weight of sample loading influenced the extraction efficiency of total phenolics and caffeine at 95% level (P < 0.05) significantly. Optimized conditions were determined as 195 °C, sample loading 0.8 g. Ten different cultivar coffees were compared under the optimized conditions, and found that total phenolics in the range of 19-26 mg GAE/g DW, DPPH activity and ABTS activity located in 16-38 mg and 10-28 mg VE/g DW, respectively. Caffeine and 5-CQA range 3-9 and 51-201 mg/g DW, respectively. The results showed that these residues processed by PLE possessed potential health benefits and could be used as an ingredient or additive in food and cosmetic industries.