Sensitive Detection of β-Myrcene in Mango Using Ethyl Cellulose Modified Quartz Crystal Microbalance Sensor

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ScienceDirect Materials Today: Proceedings 18 (2019) 1025–1032

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ICN3I-2017

Sensitive Detection of β-Myrcene in Mango Using Ethyl Cellulose Modified Quartz Crystal Microbalance Sensor Sk Babar Alia*, Barnali Ghatakb , Nilava Debabhutib , Satyaki Pala , Prolay Sharmab , Bipan Tudub and Rajib Bandyopadhyayb a

Department of Applied Electronics and Instrumentation Engineering, Future Institute of Engineering and Management, Kolkata 700150, India b Department of Instrumentation and Electronics Engineering, Jadavpur University, Kolkata 700 098, India

Abstract β-Myrcene is a type of terpenes hydrocarbons commonly emitted in substantial amounts by plants such as mango. Using piezoelectric crystal, a sensor for detecting β-Myrcene volatile by using ethyl cellulose was fabricated. This fabrication of the sensing layer involves a nebulizer which actually vibrates the coating material 25MHz frequency becoming an aerosol. The sensor was found to be sensitive, selective and precise in order to detect the target analyte β-Myrcene aroma. The sensitivity of the sensor was 1Hz ppm maintaining a linearity of 0.999. The response of the prepared sensor was validated by real mango aroma which agrees the result obtained from the raw chemical constituents. By determining β-Myrcene volatile released during pre-matured until matured period, one could use this as a data point as potential non-destructive solution to discriminate the mango ripeness stage hence improving the quality of harvest. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i2017). Keywords:Quartz crystal microbalance sensors , β-Myrcene, Mango;

1. Introduction Mango (MangiferaindicaL) is one of the most well-known and leading climacteric fruit merchandized throughout the world. Mango is in escalating commercial importance all over the globe since 2004, reputed as “fruit par excellence” [1].Recent studies unveil mangoes as an excellent source of vitamin c and folate. The energy value per * Corresponding author. Tel.: +033-2434-5640 ; fax: +033-2434-5641 . E-mail address: [email protected] 2214-7853© 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i2017).

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100 g of the common mango is estimated to be 250 kJ (60 kcal) [2, 3]. Mango is not only delicious but also rich in prebiotic dietary fiber, vitamins, minerals and polyphenol flavonoid antioxidant compounds [4]. It also contains sugar, asmall amount of protein, fats and other nutrients. Mango is mostly eaten fresh as a dessert also processed as juices, jams, jellies, nectars as well as crisp mango chips [5]. The present study indicates that all varieties of mango are rich sources of vitamin C, fiber and important minerals and safe from heavy metal contamination. Himsagar contains highest vitamin C. Langra contains high protein, fiber and sodium and hence it is anutritious variety [6]. The flavor of mango fruits is constituted by several volatile organic chemicals mainly belonging to terpenes, furanone, lactone, and ester classes [7, 8]. Different varieties or cultivars of mangoes can have flavor made up of different volatile chemicals or same volatile chemicals in different quantities. Ethylene, a ripeningrelated hormone well known to be involved in theripening of mango fruits, causes changes in the flavor composition of mango fruits upon exogenous application, as well [9].In contrast to the huge amount of information available on the chemical composition of mango flavor, the biosynthesis of these chemicals has not been studied in depth; only a handful of genes encoding the enzymes of flavor biosynthetic pathways have been characterized to date [10, 11, 12, 13]. During ripening of fruits disappearance of chlorophyll is normally associated with theunmasking of carotenoids and the fruit acquiring bright yellow-red color. Langra mango and Cavendish banana are commercially important fruits of India. Despite their pleasant pulp color, flavor and general acceptance, these fruits fail to develop yellow color due to incomplete degradation of chlorophyll when ripened at temperatures above 25-30 °C [14]. These ‘green-ripe’ fruits affect consumer preference and consequently fetch a lower price. Recently, electronic nose was used to evaluate the maturity stages of the fruit and itbecame a popular topic of research due to their fast, real time and non-invasive nature of theoperation. These systems coupled with intelligent data processing methods are able to declare results of qualitative nature with thedifferent application [15, 16, 17, 18, 19]. However, the performance of sensor array based instruments heavily relies on the sensitivity and selectivity of sensors. Metal Oxide semiconductor(MOS) sensors have been very widely used for electronic nose instruments [20, 21, 22]. Many kinds of literature report the widespread use of commercially MOS based electronic nose put to scores of different applications [17, 19]. The dependence on commercial availability is due to the fact that these sensors are difficult to develop. The situation becomes more difficult when tailor-made sensing characteristics are required. Thus choosing these sensors for a particular application is very critical. All these factors affect the sensing accuracy. In other words, low sensitivity and selectivity towards target aroma molecules. MOS sensors also require high temperature for their operation. This also reduces the portability of the instruments for field works, as the instruments require a heavier power source. Besides, these sensors are also prone to ethanol poisoning along with higher susceptibility to moisture. Quartz crystal microbalance sensors (QCM), on the other hand, can be operated at room temperature, are extremely sensitive and can be developed to operate in a very small area.G.Sauerbrey demonstrates that resonant frequency of the quartz crystal decreases if an increase in mass bound from gas- phase species on the active surface of crystal which may use to quantify the loaded mass accurately. The AT- cut quartz crystal has a superior mechanical and piezoelectric property and it maintained a good linear relationship between the frequency deviation and the mass deposition on the crystal surface [23]. ∆ =−

∆

(1)

Where A is active electrode area (0.0064 cm2), ρq is the density of the quartz crystal (2.66 g/ cm3), μq is the shear 11 modulusof cut face (μq = 2.947x10 g/cm.s2). The significant advantage of a QCM sensor for electronic nose applications is being the ease [24], with which the sensitivity and selectivity can be modulated for the target aroma molecules. Electronic nose based on QCM sensors thus can be an exciting proposition for solving many real world tasks that involve aroma detection. Table1 represent the flavor quality of volatile compounds in mango aroma. The aim of the present work is to developed quartz crystal sensor to detect the most common mango volatile βMyrcene present in different cultivars. QCM sensor is basically an AT-cut quartz crystal attached with gold electrodes and appropriate sensing material coated over the surface of the crystal. Selection of the coating material always plays animportant role for specific sensor development because it determining the selectivity of the sensor. The sensor in sensing phase the selective target analytes quickly formation of physical bonds between the coating material of the sensor [25]. The physical bonds are very weak, it discarded by fresh air allow to the sensor surface with a constant flow rate is called purging phase of the sensors. Purging process will continue until the base line of the sensor back to the original value. The sensing mechanism of a QCM sensor is shownin Fig. 1.The developed

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sensor was tested with pure mango aroma chemicals and then evaluated the sensor characteristics like sensitivity, selectivity, repeatability, and reproducibility. Table 1. Favour quality of volatile compounds responsible for mango aroma.

Volatile flavour compounds (VFC)

Flavour

3- Carene

Sweet and pungent

β - caryophyllene

Woody, spicy and tenacious

Ocimene

Woody and herbal

β - Myrcene Humelene

Musty, Spicy Woody and hay

Fig.1. The sensing mechanism of a QCM sensor

1.1. Materials QCM with gold-plated electrodes (10 MHz, AT-cut quartz crystal) was procured from Andhra electronics, Andhra Pradesh, India. β-Myrcene, 3-Carene, Humulene, Ocimene, β-Caryophyllene, and Ethyl cellulose were purchased from Sigma Aldrich, Germany. Solvent ethanolwas purchased from MERCK and Co., USA. All these chemicals are of thepure analytical grade.Agilent universal counter model 53131A was used for monitoring frequency changes and data-logging to apersonal computer. NI-6602 counter cards were purchased from National InstrumentsTMfor the monitoring of sensor frequency shift during sensor development. 1.2. Sensor development 10 MHz AT- cut quartz crystal microbalance with Au- electrode was used as thesubstrate. The gold surface was cleaned pure ethanol solution.In this study, blank quartz crystal was fabricated with a polar and hydrogen bonding intermolecular forces material ethyl cellulose and ethanol with concentration 0.05% (w/v) heated for the preparation of sensor coating solvent then it was deposited on agold electrode of crystal sensor by a nebulization method shows in Fig.2. [25]. In this method, a solution of sensor-active material is loaded into a nebulization cup.A fine mist producing from coating solution by using theultrasonic vibrating method. This fine mistis then released from the nebulizer outlet with a fixed flow rate and then deposited on the cleanedcrystal electrode surface fabricating homogeneous and uniform coating.

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Fig.2. Schematic of nebulization spray coating method.

1.3. Experimental setup The main aim behind setting up this experimental setup was to study the sensitivity, selectivity, repeatability, and reproducibility of the developed sensor. The sensor consists of a 100ml air tight chamber made of Teflon. The Teflon chamber is kept at a controlled environment maintained at 28.2̊ C and relative humidity of 47%. Due to the gaseous nature of the target analyte, carrier gas was not considered in this experiment. A 300ml air-tight Teflon chamber was used when a series of 8 sensors were used. The sample was made to inject into the sensor chamber with the help of a glass syringe over a rubber septa attached to one end of the arms of a three way valve. The gases were watchfully dispersed in the chamber so that it affects the sensor in minimum time but with maximum effect. However cares were taken to ensure that the effect of syringe flow rate had no reflection in the result. The sampling duration was continued till the response of the sensor attained equilibrium with the target gas environment. Signal connections were taken to the counter instrument with the help of the QCM sensor attached to the rigid base. The current frequency of the sensor was displayed through a counter. The output in the form of current frequency was also sent to a personal computer for data-logging. After sampling, the sensors were purged for a short time interval with the help of a suction pump that pumped out the analyte gases outside the chamber with an intention to bring back the sensor to its baseline value. The experiment setup for the experiment is shown in Fig.3.

Fig.3.Measurement setup with single QCM sensor.

1.4. Reproducibility and repeatability of QCM Sensors Reproducibility is the measurement that shows to what extent an experiment or process maintains its identical results, performed either by the same observer or someone else provided all the external conditions are maintained at

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thesame level. In this experiment, all the quartz crystal microbalance sensors were fabricated through similar coating process in order to satisfy the need of similar conditions for measuring the reproducibility of the sensors. QCM sensors were coated with ethyl cellulose. The percentage of reproducibility (RD) of the sensors was calculated keeping in mind the relative standard deviation (RSD) of the fabricated sensors in different concentration of target gas. The calculation of RD as shown in (2) was repeated and the average reproducibility was considered. RD,P = (1-RSD) ×100

(2)

RD values are related to RSD values in such a way that lower the RSD values, higher will be the RD values. Thus better reproducibility of the sensors was achieved by maintaining lower RSD values. Repeatability of the sensor is the measurement of identical response produced by an individual sensor upon repeated implementation of a volatile gas of fixed concentration. The percentage of Repeatability (RP) of the developed sensors was introduced to β-Myrcene gas of different concentrations. The responses of all individual sensors were considered for calculating the relative standard deviation (RSD) and the average RPof the sensors were calculated using (2). 1.5. Evaluation of sensitivity and selectivity of the QCM sensors Sensitivity and selectivity major two parameters of the developed sensor was measured by pure mango volatile varying from 10 ppm to 1000 ppm to the sensor chamber using an automated syringe pump (Unigenetics Instruments Pvt. Ltd. India, NE-1000) and sensor response were detected by real time frequency meter and recorded it by data logger (Agilent 82357B). Analysis the sensitivity and selectivity of the sensor towards the specific mango volatile were carried out from the Frequency deviations of the sensors. 2. Result and discussion 2.1. Sensitivity and Selectivity of the QCM Sensor β-Myrcene is one of the important volatile constituents in mango. To detect the specific aroma from mango, a selective sensor was developed in order to detect the chemical in mango. Ethyl cellulose has been chosen a sensing material for this detection purpose. The sensor was fabricated using nebulization technique. The prepared solution was poured into the chamber where the liquid is subjected to avery high frequency of around 25 MHz. The liquid is deposited on the crystal surface in the form of anaerosol which was monitored by deviation of crystal frequency from the baseline. The β-Myrcene gas was prepared and subjected to the developed crystal using an automated syringe pump at a rate of 100 ml/min. The sensor was able to sense the target aroma from 10 ppm- 1000 ppm concentration with asensitivity of 0.1 Hz /ppm (R2=0.99). The air was purged reasonably after each experiment to bring back the crystal to its base value. The sensor profile and calibration curve of the sensor were represented in Fig.4, 5. respectively.

Fig.4. The sensor profile of the developed QCM sensor at 800 ppm of β-Myrcene gas.

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Fig.5. The calibration curve of the developed QCM sensor to 10 ppm -1000ppm β-Myrcene gas.

As the mango contains anenormous amount of volatile organic compounds, it’s very imperative to verify whether the developed sensor is able to detect the target volatile organic compounds (VOC) selectively. To test this, the sensor was subjected to other significant aroma presented in mango namely, ocimene, beta- Caryophyllene, 3Carene and humulene. From the Fig. 6. it was observed that beta- Caryophyllene, 3- Carene and Ocimene vapors interfered negligible in the sensor output. The sensing material, ethyl cellulose was chosen as its very important flavor encapsulating material having repeated no of ethyl ether groups.

Fig. 6. Bar plots representing selectivity of QCMsensor β-Myrcene, ocimene, β- Caryophyllene, 3- Carene and humulene.

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2.2. Repeatability and Reproducibility of the QCM Sensor β-Myrcene pure mango volatile varying from 10 ppm to 1000 ppm concentration, ten times repeatedly injected to the sensor chamber where the developed sensor was rigidly mounted and frequency deviation was recorded for each measurement. The percentage repeatability of the sensors was calculated by using the Eqn 2. The sensor shows amore repeatable response at ahigher concentration that is for 10 ppm the percentage repeatability is 97.96% where for 1000ppm the percentage repeatability is 99.9%. and the average repeatability considering all concentrations is 99.28%. For evaluating reproducibility, eight quartz crystal coated with the ethyl cellulose sensingmaterial and considering all the sensor development parameter is keeping constant. All developed sensor attached to the sensor chamber and different concentration of β-Myrcene (10ppm to 1000ppm) were applied repeatedly. The percentage of reproducibility (RD) was calculated from the response of all the sensors. The average percentage of reproducibility is so good, its value is 99.15 which indicate one sensor can be replaced with the other sensor with some negligible loss. The percentage of repeatability and reproducibility for eight sensors has been shown in Table 2. Table 2. Repeatability and reproducibility measures of the developed sensor

Concentration

Repeatability

Reproducibility

(ppm) 10

RP (%) 97.96

RD (%) 99.98

100

98.91

98.63

300

99.46

98.85

500

99.69

99.08

700

99.75

99.14

900

99.9

99.19

3. Conclusion In this study, the ethyl cellulose was effectively used for development of quartz crystal microbalance gas sensor for detection of β-Myrcene mango aroma. The sensor shift 0.1 Hz frequency per single ppm concentration of βMyrcene mango volatile, that indicate sensor strongly sensitive to thetarget analyte. The sensitivity and selectivity has been carried out, the sensitivity towards β-Myrcene is 0.1Hz/ppm, whereas 3-Carene is 0.04 Hz/ppm, humulene is 0.014 Hz/ppm, ocimene is 0.042Hz/ppm and β-caryophyllene is 0.057Hz/ppm it indicated that the QCM sensor more selective towards β-Myrcene rather than the other mango aroma. Ethyl cellulose generally used for flavor encapsulation purpose, β-Myrcene is mango aroma and it plays an important role in thecase of unripe mango smells. On the other hand, the sensor is established to agood percentage of repeatable and reproducible and average RP and RD value of 99.28% and 99.15%, respectively.Further work may be carried out by estimating correlation of the developed sensor with gas chromatography estimation of β-Myrcene in real tomato samples. References [1] I.A. Rajwana, A.U. Malik, A.S. Khan, B.A. Saleem, S.A. Malik, A new mango hybrid shows better shelf life and fruit quality Pak, J. Bot., 42 ,2010, pp. 2503-2512. [2] M. Lauricella, S. Emanuele, G. Calvaruso, M. Giuliano, A. D. Anneo, Multifaceted Health Benefits of Mangifera indica L. (Mango): The Inestimable Value of Orchards Recently Planted in Sicilian Rural Areas, J. Nutrients, 9 525, 2017, pp. 1-14. [3] M.A. Islam, S. Morshed, S. Saha, F.B. Quader, M.K. Alam, Evaluation of Nutritive Value of Mango Juices Found in Bangladeshi Markets, J. Environ. Sci. & Natural Resources, 8 1, 2015, pp. 95-98. [4] S. Ahmed , Home Healing with Nature's Medicines, Xlibris Corporation, 2013, ISBN 978-1-4931-5019-9. [5] M.S.Hamdard, M.R. Rafique, U. Farroq, Physico – chemical characteristics of various mangos, Mangifera indica L. varieties, J. Agricultural Research 42(2), 2004, pp.191-199. [6] R. Ara, M. Motalab, M.N. Uddin, A.N.M. Fakhruddin, B.K. Saha, Nutritional evaluation of different mango varieties available in Bangladesh,International Food Research Journal 21 6, 2014, pp.2169-2174.

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