187 Antioxidant and Antimicrobial Activities of Spent Coffee Residues K. Chotanakoon and M. Naradisorn Discipline of Technology of Management of Agricultural Produces and Packaging School of Agro-Industry Mae Fah Luang University Chiang Rai Thailand Keywords: antimicrobial activity, antioxidant, spent coffee residue, Colletotrichum sp., Lasiodiplodia theobromae Abstract Spent coffee residue is a by-product of coffee processing and its disposal is a matter of concern. Coffee residues, however, have been reported to be useful as fertilizer, animal feed, and fuel. Chemical analysis has shown that phenolic compounds, which are responsible for antioxidant and antimicrobial activities, still remain in spent coffee residues. This study aimed to investigate the antioxidant and antimicrobial activities of spent coffee residue extracts. Spent coffee residues of two coffee cultivars ‘Arabica’ and ‘Robusta’ were extracted either with water ± microwave power or with 70% ethanol ± microwave power. The coffee residues extracted with water in combination with microwave power (800 watt, 30 s) had a significantly greater (P<0.05) total phenolic content than those extracted with solvent only. Likewise, the strongest ability to scavenge DPPH was detected in coffee residues extracted with water in combination with microwave power. Extracts of ‘Robusta’ spent coffee residue had more total phenolic content, and showed greater antioxidant activity than extracts of ‘Arabica’. Both ‘Arabica’ and ‘Robusta’ extracts had no antimicrobial activity against two postharvest pathogens: Colletotrichum sp. and Lasiodiplodia theobromae. INTRODUCTION Coffee is one of the most widely consumed beverages throughout the world and its consumption has been increasing (Nebesny and Budryn, 2003). Thus, the disposal of spent coffee residue becomes a major problem encountered by the industry, and has become a matter of concern. Several attempts have been made to utilize coffee residues. However, chemical analysis has shown that naturally occurring phenolic compounds, which are responsible for antioxidant and antimicrobial activities, are present in coffee residues. The phenolic compounds are known to contribute to quality and nutritional value, and are also important in plant defense mechanisms to protect plants themselves from attack and damage by microorganisms, insects, and herbivores (Sengul et al., 2009). Antibacterial activity of coffee against Gram-positive and Gram-negative species has been reported (Nebesny and Budryn, 2003; Ana et al., 2006). The antimicrobial activity of coffee residues is still unclear; therefore, this study aimed to investigate the antifungal property and antioxidant activity, including bioactive compounds, of spent coffee residues. MATERIALS AND METHODS Materials Spent coffee residue ‘Arabica’ was obtained from Shong café, a coffee shop in Mae Fah Luang University, Chiang Rai, Thailand. The ‘Robusta’ ground coffee was purchased from a coffee shop in Malaysia, and was processed to obtain the residues. The spent coffee residues were dried at 60°C for 72 h and stored in desiccators until use. Folin-Ciocalteu phenol reagent was purchased from Fluka Chemie AG (Buchs, Switzerland), and gallic acid and 2,2-Diphenyl-1-picryl-hydrazyl (DPPH) were purchased Proc. IC on Postharvest Pest & Disease Mgt. Exporting Hort. Crops Eds.: C. Hale and P. Jitareerat Acta Hort. 973, ISHS 2013