# E-Nose Quality Evaluation of Extra Virgin Olive Oil Stored in Different Containers
## 2 Materials and Methods
### Analyses
#### 2.2.3 Electronic Nose  
The miniaturized electronic device (with an electronic board measuring 39 mm \(\times\) 33 mm) was used in this study, and it was designed and developed in-house by the Department of Electrical, Electronic and Automatic Engineering of the University of Extremadura (Spain) [23]. The electronic device is shown in Figure 1 and has the desired features of portable equipment: it has very low power consumption (185 mA), it is powered by a 3.7 V\({}_{\text{DC}}\) and 2000 mAh rechargeable LiPo battery, it is lightweight and small in size, and can transfer data wirelessly to a smartphone. All these features make it manageable when taking measurements from the tasting glasses. The E-nose board has two different power supplies (+3.3 VDC and +1.8 VDC) for the different sensors and is governed by a powerful microcontroller (PIC32 MM0256 GPM048 from Microchip Technology Inc., Chandler, AZ, USA). Among other features, this microcontroller has been chosen because of its memory (256 KB of program memory and 32 KB of data memory) and its communications modules (several I2C and UART). The E-nose also has a Bluetooth module (Microchip's RN4871), a UART port serial communication, and a battery charger via micro-USB-B connector. The sensors used ([PERSON] et al., 2021a) are grouped into an array of 11 Metal Oxide Semiconductor (MOS) sensors inserted into four chips with integrated analog-to-digital converter and I2C bus communications: BME680 from Bosch Sensortec GmbH (Reutlingen, Germany), SGP30 from Sensirion AG (Stafa, Switzerland) and CCS811 and iAQ-Core from ScioSense B.V. (AE Eindhoven, The Netherlands). These sensors send a total of 14 signals, distributed as follows:  
* BME680: ambient temperature (oC), pressure (hPa), relative humidity (% RH), and gas measurement (\(\Omega\)).
* SGP30: equivalent CO\({}_{2}\) concentration (eCO\({}_{2}\)) (ppm), total volatile organic compounds concentration (TVOC) (ppb), and the raw measurements of H\({}_{2}\) and ethanol.
* CCS811: eCO\({}_{2}\) (ppm), TVOC (ppb), and sensor resistance (\(\Omega\)).
* iAQ-Core: eCO\({}_{2}\) (ppm), TVOC (ppb), and sensor resistance (\(\Omega\)).  
The same procedure described for the sensory analysis was followed to carry out the E-nose analysis of the VOO samples. The samples selected for each sampling date during the shelf life were frozen at \(-\)80 \({}^{\circ}\)C until the time of analysis. Samples were then subjected to a cold defrost for 48 h and placed into the tasting glass as previously described in the sensory analysis epigraph. The E-nose data consisted of a static headspace adsorption phase, where the aroma of the samples was put into contact with the E-nose sensors for 60 s. The E-nose was then placed into a tasting glass containing a silica gel cup for 30 s until the desorption phase took place and to bring the gas sensor signal back to the baseline. The operational temperature of the sensors (around 400 \({}^{\circ}\)C) was optimized for this application and selected through the user interface. The E-nose recorded data at one second intervals and the system took a reading of the resistive value supplied by each sensor. The E-nose measurements were made randomly on the tasting glasses, making ten measurements for each VOO sample. The values detected by the sensors were read by a microprocessor, which sent them to a smartphone via Bluetooth using an ASCII-based protocol. All signals were sent at the same time separated by tabs in a single row, and each measurement was sent every second, resulting in a table in which each column corresponded to a signal and each row to a measurement. An Android application with an easy user interface was developed to fetch and save this data for further processing. The resulting data were then sent to a computer and organized into columns in a spreadsheet for chemometric analysis.