## 2 Materials and Methods
### Estimation of Phenolic Content and Antioxidant Potentials
#### 2.4.9 Reducing Power Assay (RPA)  
The estimation of reducing power in fermented and unfermented coffee was conducted using the modified method developed by [PERSON] et al. [18], which is indicated by a color change from yellow to green. In this assay, 10 \(\upmu\)L of sample or standard was added to the plate, followed by the addition of 25 \(\upmu\)L of a 0.2 M phosphate buffer (pH 6.6) and 1% potassium ferricyanide (III) solution. The plate was then incubated at room temperature in the dark for 20 min. After incubation, 25 \(\upmu\)L of 10% trichloroacetic acid, 85 \(\upmu\)L of water, and 8.5 \(\upmu\)L of 0.1% ferric chloride solution were added to the plate. The plate was incubated under the same condition for an additional 15 min. Trolox in ethanol solution ranging from 0 to 500 \(\upmu\)g/mL was used as the standard, and the sample in water was used as the blank. The results were measured after the last 15 min incubation and expressed as milligramsof Trolox equivalents per gram of coffee powder on a dry weight basis (mg TE/g) with standard deviation (SD). Liquid Chromatography-Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry (LC-ESI-QTOF-MS/MS)  
The characterization of phenolic compounds was performed using the LC-ESI-QTOF-MS/MS method, which was generated and modified by [PERSON] et al. [19] and [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] [11]. The analysis involved the use of an Agilent 1200 series HPLC coupled with an Agilent 6520 Accurate-Mass Q-TOF LC/MS system equipped with an electrospray ionization source (ESI) for initial identification and characterization. The sample separation was carried out by a Synergi Hydro-RP 80A LC column (250 mm \(\times\) 4.6 nm, 4 \(\upmu\)m) (Phenomenex, Lane Cove, NSW, Australia) at 25 \({}^{\circ}\)C. The mobile phase consisted of 98% acetic acid in water (mobile phase A) and a mixture of acetonitrile, water, and acetic acid in a ratio of 100:1:99 (\(v/v/v\)) (mobile phase B). Mass spectra were obtained in the \(m/z\) range from 50 to 1300, and peaks were identified in both positive and negative ionization modes. The acquisition and analysis of data were conducted using Mass Hunter Data Acquisition Software Version B.03.01 (Agilent Technologies, Santa Clara, CA, USA) and Personal Compounds Database and Library (PCDL). For compounds that exhibited a mass error lower than 5 ppm and a PCDL score above 80, further MS/MS identification and \(m/z\) characterization were carried out. Headspace Solid-Phase Microextraction Coupled to Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS)  
The identification and semi-quantification of volatile compounds in ground coffee samples were analyzed via HS-SPME-GC-MS following the methods by [PERSON] et al. [20] and modified by [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] [11]. The analysis involved utilizing a gas chromatograph (6850 series II Network GC System, Agilent Technologies, Santa Clara, CA, USA) coupled with an HS-SPME system (PAL RSI I20, CTC Analytics AG, Zwingen, Switzerland) and a mass spectrometer (5973 Network Mass Selective Detector, Agilent Technologies, Santa Clara, CA, USA). A 30 m DB-Wax capillary column (Agilent Technologies, Santa Clara, CA, USA) with an internal diameter of 0.25 mm and a film thickness of 0.25 \(\upmu\)m was selected, along with a 65 \(\upmu\)m PDMS/DVB fiber (Fused Silica, Sigma Aldrich, St. Louis, MI, USA). Helium was used as the carrier gas with a column head pressure of 60 kPa, and samples were incubated at 60 \({}^{\circ}\)C for 15 min, followed by a 15 min extraction and a 6 min desorption period. The GC oven program was set as follows: it started with an initial temperature of 40 \({}^{\circ}\)C for 5 min, followed by a gradual increase to reach 190 \({}^{\circ}\)C at a rate of 5 \({}^{\circ}\)C/min and was kept at that temperature for 8 min. Later, the temperature was further raised to 240 \({}^{\circ}\)C at a rate of 10 \({}^{\circ}\)C/min and maintained for 10 min.