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obtained from the fermentation process, the curing process, the roasting process, as well as the brewing process. This brewing process is not only produced the drink, but also generates coffee
ground residue CGR as the side product. CGR is normally dumped directly to the bin. This causes a lot of environmental problems to the community.
Figure 2 Processing of Coffee Fruit into Beverages FAO, 2012
B. COFFEE GROUND RESIDUE CGR
Coffee ground residue CGR is a by-product of brewing process after the drink is extracted from coffee bean ground. Coffee ground residue usually discarded as a solid waste.
Nowadays, there are increasing number of coffee ground residue as a result of the growth of coffee shop business. There are approximately 6,000,000 tons of coffee ground residue produced every
year in the world Tokimoto et al., 2005. Producing one kilogram of soluble coffee will generates
2 kg of wet CGR and about one ton of green coffee generates about 650 kg of CGR Pfluger, 1975.
Coffee ground residue
Mucilage De-hulling
Fermentation Selection
Washing Water
De-hulling Hulls
Drying Coffee husk
Roasting Grinding
Drying Cleaning
Coffee pulp
Brewing
Coffee beverages De-pulping
Washing Coffee cherries
Dry process Wet process
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The CGR will cause environmental problems. Although CGR is biodegradable materials, the better decomposition process will take much time and needs a large landfill. These has
motivated people to reutilize CGR for biofuel production Silva, 1998, polysaccharide sources Simones et al., 2009, or pharmaceutical and nutraceutical compounds anonymous, 2012, in
order to reduce the environmental problem and to add up value to the residue. Various works also showed that coffee ground residue still contains a certain amount of bioactive compounds such as
phenolic compounds, chlorogenic acid, and flavonoids Mussato et al., 2011. These compounds especially chlorogenic acid are powerful in-vitro antioxidants Yen et al., 2005. The amount of
these compounds in CGR are depended on various factors, for instance, coffee varieties, pre and post-harvest handling , brewing machine performances Cruz, 2011 and the extraction methods
Chirinos, 2011.
C. MICROWAVE ASSISTED EXTRACTION MAE
Microwave oven has become an essential appliance in most of kitchen in the past 20 years. The primary benefits of microwave oven are faster cooking times and energy savings over
conventional methods. Although the use of microwaves for cooking food is widespread, the application of this technology to the processing of materials is a relatively new development.
Nowadays, microwave has been applied to extract and isolate phyto-constituents. Microwave is electromagnetic non ionizing waves, frequented between 300 MHz to 300 GHz,
positioned between X-Ray and infrared in electromagenetic spectrum. The microwave is made by two oscillating fields; electric field and magnetic field which are responsible for heating Letellier
et al., 1999. Microwave-assisted extraction MAE is a system used to selectively extract target compounds from various raw materials with microwave energy Jain et al., 2009. MAE is a close
system that performed with higher temperature which can reduce extraction times drastically. As compared to conventional thermal processing that transferring the energy to the material trough
convection, conduction, and radiation of heat from the surfaces of the material, microwave energy is delivered directly to materials trough molecular interaction with the electromagnetic field. In
heat transfer, energy is transferred due to thermal gradients, but microwave heating is the transfer of electromagnetic energy to thermal energy and is energy conversion, rather than heat transfer.
This difference in the way energy is delivered can result in many potential advantages to using microwaves for processing of materials.
There are two principles of heating using microwave; 1 based upon its direct impact with polar materialsolvent, and 2 governed by two phenomenons: ionic conduction and dipole rotation
Letellie et al., 1999. Ionic conduction is electrophoretic migration of ions generate friction which responsible for heating the solvent, while dipole rotation is realignment dipoles of the molecules in
changing of electric field rapidly frequency 2450 MHz, 4.9 x 104 times in changing the electric field Zuloaga, 1999.
The materials normally have moisture inside the matrix. Microwave will heat up the water molecules in the plant cells which then evaporated, and generated tremendous pressure to
cell walls. The pressure will facilitate the leaching out of some constituents from the rupture cells into the solvent Wang et al., 2006. Microwave extraction effect on some conditions, such as
destroying the surface of sample because of sudden increasing of temperature and internal pressure, rapid exudation of the chemical substances within the cells into surrounding solvent, and
the migration of dissolve ions increased solvent penetration into matrix Garcia-Ayusa et al., 2000.
There are several factors affecting MAE systems; 1 type of solvent and the volume, 2 extraction time, 3 microwave power, 4 temperature and 5 matrix characteristic Mandal et al.,
2007. These factors can influence amount of materials leaching out from the matrix. Recently, dielectric heating or microwave heating becomes attractive technique for
improving extraction yield and improve amount of bioactive compounds in some sources. Application of MAE was reported by several research groups. Coffee bean extracted by
microwave were having higher yield of chlorogenic acid and caffeine than those in conventional heat reflux Upadhyay, 2011. MAE could extract flavonoid in Chinese herb Radix puerariae in
different extraction time, solvent, and microwave power Wang et al., 2010. Although MAE made high temperature inside matrix but the pressure could leach out the bioactive compounds
into solvent faster.
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D. BIOACTIVE COMPOUNDS
