Real clip runing system based electronic olfactory organ was developed with an array of commercial metal oxide semiconducting material ( MOS ) detectors and homemade Zn oxide based detector, for existent clip quality analysis of natural milk. The detectors were empanelled and calibrated towards assorted concentrations of volatile organic compounds ( VOCs ) such as ethyl alcohol, hexanal, acetic acid, ethanal, etc. , which are responsible for off-flavors in milk produced due to microbic taint, chemical reactions and familial effects in cow. In add-on to MOS detectors, an electrochemical based C dioxide ( CO2 ) detector was incorporated in the detector array and calibrated towards assorted concentrations of CO2 to observe the spoilage of milk due to mastic disease in cattles. The selectivity and favoritism efficiency of developed electronic olfactory organ was confirmed with chief constituent analysis.
Natural smells are complex mixtures of little organic molecules with comparative molecular multitudes in the scope of 18 to 300 micrometers [ 1 ] that are carried by air along with many other chemical compounds. The smell belongingss, including perceived strength, of a molecule depend on the form, the size and features of the polar group, so that a low volatility species can be sensed intensely, while the other nowadays in high concentration can hold merely a low strength odor. Smell may acknowledge a harmful substance, but more often it will be sensitive to natural and harmless compounds that result from biological procedures. Electronic nose, a mimic of human smell, plays a decisive function in nutrient quality favoritism, where human sense of odor fails due to tire, narrowness in sensing bound and exposure to toxic organic compounds. Since quality control of get downing milk is one of the most of import undertakings in the production of dairy merchandises [ 2 ] and chemical analysis in the milk remains a great challenge to the centripetal rating panel for many decennaries due to the heterogenous nature of milk [ 3 ] , a demand for rapid and cost effectual favoritism of milk and dairy merchandises becomes significant. At this occasion, electronic olfactory organ, an array of gas detectors with pattern acknowledgment system came to the scenario in order to replace the extremely sophisticated analytical instruments ( for illustration, mass chromatograph, FTIR and UV-Visible spectrometer ) whose use is being limited chiefly because of their higher cost and deficiency of portability, despite their truth. Analysis of milk olfactory property is the best promising tool to obtain information about the milk and one of the best methods to insulate the spirit compound is headspace analysis [ 3 ] . Headspace of milk from a healthy cow typically contains complex mixtures of VOCs ( propanone, 2-pentanone, 2-butanone, methylbenzene, limonene, heptanal, etc. ) at assorted concentrations [ 3-5 ] . The concentration of these VOCs varies due to the factors such as bacterial metamorphosis, ageing, photo-oxidation and presence of pro-oxidant metals such as Cu, Fe and Ni.
Milk from a healthy cow contains merely few bacteriums which, may multiply and the rate of generation will increase, as clip base on ballss from the clip of milking to the clip of processing ; it besides depends on the criterion of milking, managing patterns and storage. These bacterial growings, lead to the spoilage of milk with the production of off-flavor. As the microbic spoilage of get downing milk badly affects the industrial quality, due to unwanted olfactory property, physical defects and metabolic toxicity, designation of spoilage in milk before production of merchandises becomes compulsory. Likewise, spoilage of milk due to assorted other factors should besides be identified at the earliest phase to avoid complications and ailments in the concluding merchandise. This can be achieved by early sensing of VOCs at headspace [ 5 ] produced during spoilage. Fox illustration, milk spoilage due to microbial/bacterial taint can be identified from the presence of ethanal, 3-methyl-1-butanol, acetic acid and ethanol [ 4, 6 ] in headspace of the milk, which are absent in natural milk before spoilage. Likewise hexanal, pentanal and dimethyl disulfide [ 4 ] are good indexs of fluorescent visible radiation damaged merchandises. Whereas pentanal, hexanal, heptanal and isopentanal will bespeak Cu induced oxidization in milk [ 7 ] ripening of milk can be significantly identified through the presence of dimethyl sulphide, ethyl ethanoate, 2-heptanone, pentanal, etc. [ 8 ] . Ampuero et.al, [ 4 ] observed that the headspace of milk from the cow bearing familial defect contains trimethyl aminoalkane. And Erikssona et.al, [ 9 ] observed that the milk from the cow affected by mastic disease contains higher concentration of CO2 than the healthy mention milk.
From the literature it is noted that, so far to know apart the quality of milk and their derived functions, detectors of assorted sort were exposed to the headspace of milk samples of assorted ages or stored under assorted status or from assorted farms after interventions and most widely used, pattern acknowledgment methods like rule constituent analysis ( PCA ) [ 2, 10 ] or unreal nervous web ( ANN ) [ 4, 11 ] has been carried out. Though PCA is a traditional method of analysis and cut down the dimensionality factor, during existent clip analysis it is non user friendly. These require boring preparation procedures and feverish sample aggregations.
Hence in order to do sensor systems portable, cheaper or useable for supervising nutrient quality, detector elements and system as a whole: should necessitate low power for operation ; should hold no demand for external bearer or reactant gases ; should be made compatible with microelectronic engineerings ; should hold reversible and consistent responses ; should hold equal sensitiveness and should hold response times lower than one minute and long term stableness if used in uninterrupted operation or response times of a few seconds. With this motive in head a Real Time Operating System ( RTOS ) based embedded electronic olfactory organ system that can observe the volatile organic compounds ( VOCs ) as given in Table 1 which are good marker for milk spoilage due to assorted grounds has been developed.
Since the electrical belongingss of the metal oxide semiconducting materials vary [ 12-14 ] harmonizing to the environment to which they are exposed through the procedure of surface assimilation / desorption, the metal oxide semiconducting material ( MOS ) based detectors are found to be suited campaigners for observing VOCs / gases at assorted concentrations in the scope of parts per million ( ppm ) . Hence commercial MOS and homemade detectors were used to organize the detector array in embedded electronic olfactory organ. Further to avoid complications in the concluding embedded theoretical account inactive headspace analysis was carried out.
II. MATERIALS AND METHODS
As TGS 2620, 822, 813 ( FIGARO, Japan ) which are made of SnO2 ( n-type stuff ) [ 15 ] and homemade nanostructured zinc oxide ( ZnO ) thin movie based detectors are sensitive towards aromatic compounds of our involvement, they were empanelled to organize the array to build an electronic olfactory organ. The nanostructured ZnO n-type stuff [ 14 ] thin movie was coated on an ultrasonically cleaned glass substrate utilizing spray pyrolysis technique by fade outing 0.05 M of zinc ethanoate dihydrate ( 99.9 % pureness, Merck, India ) in 50 milliliter of deionized H2O at an optimized status. The Structural word picture of the movie was carried out utilizing X-ray diffractometer with Cu Ka radiation of wavelength 1.5418 & A ; Aring ; ( D8 Focus, Bruker, Germany ) at the scanning rate of 0.02 & A ; deg ; /min and generator scene of 40 kilovolt. Surface morphology was obtained from field emanation SEM ( FE SEM, 6701F, JEOL, Japan ) . The X-ray diffraction form of as-deposited movie shown in Fig. 1 ( a ) indicates polycrystalline nature of movie with hexangular wurtzite construction. The peak places are good in understanding with JCPDS ( File no 36-1451 ) . The SEM micrograph shows spherical shaped good connected nanograins and is shown in Fig.1 ( B ) .
Electrical word picture of these detectors was performed with the place made proving chamber. The proving chamber consists of 6500cc capacity glass jar with a septum proviso at one side of the jar to shoot desirable concentration of VOCs/gases and another side of the jar had a proviso to link the chamber to hoover pump. The proving chamber has been pumped down to low force per unit area, to heighten the response of detectors towards specific VOC.
Each detector component has been separately calibrated towards assorted concentrations of VOCs. The standardization process initiated with the preheat intervention [ 15-19 ] of detector component in order to take the ambient wet. The detectors were allowed to make equilibrium status by puting it in dry environment. Equilibrium province was determined by measuring the stableness of the detector response with regard to clip. If the mensural oppositions appear to be stable so a steady baseline is recorded and known concentrations of VOCs viz. acetaldehyde, acetic acid, dimethyl sulphide, hexanal, ethanol ( Merck, Germany: pureness – 99.8 % ) , trimethyl aminoalkane ( Alfa Aesar, USA: pureness – 99.8 % ) , were injected into the glass chamber through the graduated syringe via septum proviso separately. The attendant response of the detectors in that environment was observed under optimized status. After each exposure, dry air was allowed into the proving chamber to take the VOC from the detector environment and restore the same baseline for the following chemical exposure. Each measuring was repeated three times in order to precisely gauge and graduate the response of detectors towards specific VOC and to do certain the duplicability of the detector response.
Since the presence of higher concentration of CO2 is a good marker for milk affected by mastic disease, C dioxide detector, TGS 4161 ( FIGARO, Japan ) [ 20 ] was inducted as a 4th detector in the electronic olfactory organ. The block diagram of the apparatus used to graduate CO2 gas detector is shown in Fig.2. The preheated detector was placed inside a high vacuity gas-testing chamber ( HINDHIVAC- 12A4D Model ) . Desired concentrations of CO2 was admitted inside the chamber along with N ( N2 ) as bearer gas [ 21,22 ] through mass flow accountants ( AALBORG-USA ) and the response of detector towards assorted concentrations of CO2 was acquired utilizing ( Keithley- 6517A ) electrometer, which is integrated with the personal computing machine.
From the ascertained detector response, standardization tabular array has been formed to build the look-up tabular array, which is being embedded in the microcontroller AT89C51rd2. In the search table formation, different threshold degrees were fixed as per the response of single detector in array towards selected VOCs along with it response and recovery clip.
For existent clip quality analysis of milk and dairy merchandises, detector signals were conditioned utilizing op. amp IC TL279 and converted into their several digital informations utilizing IC AD0808. Response of all the four detectors was collected. And the detector, which showed steep fluctuation to that peculiar existent clip environment in the detector array, was identified by comparing the response of each detector to their several nothing ppm degree. Further, the response of the identified detector was compared with the corresponding calibrated informations in the embedded database for decision-making.
In the present embedded attack, concluding consequence was fixed non merely based on the steep initial response of a peculiar detector but besides depends on the response of the other detectors in the array which showed important gradual fluctuation with an addition in concentrations of that peculiar VOC/gas. Harmonizing to the end point informations and the corresponding threshold bound for decision-making, concluding consequence was displayed in the LCD faculty and the same was stored for farther processing. This was efficaciously carried out utilizing Keil Compiler and RTOS package RTX-51. In the RTOS based embedded cryptography, unit of ammunition redbreast undertaking programming was provided to read the sensor signal at a peculiar clip interval ( based on the response and recovery clip ) and hence choice of peculiar detector end product from an array was achieved. In add-on, the electromotive force end product from each detector was compared at different clip intervals after the exposure to headspace.
The efficiency of developed theoretical account in existent clip quality analysis was studied by roll uping natural milk from local farms without any preservatives and heat interventions. The detector array was exposed straight to the headspace of milk samples at 3 centimeter distance and the response of each detector was observed. Further to reconfirm the efficiency of embedded theoretical account in know aparting milk quality most widely used traditional PCA was performed utilizing MATLAB with the informations matching to assorted concentrations of VOCs and response of milk during existent clip analysis. Further, the efficiency of the theoretical account was crosschecked through gas chromatography ( GC ) ( PerkinElmer Clarus500 ) with Elite-5ms capillary column ( 5 % Phenyl 95 % dimethylpolysiloxane ) of length 30m and id 250µm. He @ 1ml/min was used as bearer gas with an oven and needle temperature of 308 K and 363 K severally.
III. RESULTS AND DISCUSSION
In the current probe, VOCs which are preponderantly responsible for the unwanted olfactory property / off-flavor during milk spoilage were presented to the detector array and response of the detector array was observed. In this subdivision methodological analysis carried out to organize the expression up tabular array and the database for determination devising during existent clip analysis of milk quality is discussed.
A. Response of detectors towards VOCs
Assorted concentrations of hexanaldehyde were presented to the detector array and the response of each detector was observed. From the response curves of detectors it was observed that as the concentration of hexanaldehyde additions, electromotive force bead across burden opposition ( VRL ) in the detector ‘s measuring ( 15-18 ) circuit additions. This is because, when MOS exposed to the environment holding VOCs, O ( O2 ) get adsorbed on the surface of MOS by taking negatrons from MOS as shown in equation ( 1 ) . Further the O2- on the surface of feeling element react with VOC and give up negatrons to the feeling stuff as expressed in equation ( 2 ) .
O2 + 2 e- ( MOS ) O2- ( 1 )
( X+ ) + O2- ( Y ) + e- ( 2 )
Where, X and Y represent the analyte and attendant merchandise severally. This consequences in an addition in charge bearers of the detection component, which in bend increases the conduction of MOS in the presence of VOCs [ 14 ] . Since the burden opposition was connected in series with the detector component, the electromotive force bead across. Therefore alteration in the value of VRL at each concentration was observed.
Similarly assorted concentrations of DMS, ethanal, acetic acid, ethyl alcohol and TMA were presented to the detector array and the response of each detector was observed and is shown in Fig. 3. From these response curves of detectors it was observed that in the instance of hexanaldehyde, as the concentration of hexanaldehyde additions, TGS 822 detector shows gradual fluctuation. Likewise for ethanal and acetic acid, TGS 2620 and 813 exhibited gradual fluctuation severally. Hence response of TGS 2620 was taken in to consideration for determination devising in the instance of presence of ethanal and 813 for acetic acid.
By following the same process, the response of the detectors array towards ethyl alcohol, DMS and TMA were observed and the detector TGS 813 found to react good for ethyl alcohol. In the instance of DMS all the detectors exhibit higher sensitiveness. Hence response of all the detectors in the array was taken in to consideration for the sensing of DMS.
Compared to other detectors in the array, response of ZnO thin movie towards TMA was found to be appreciable with better sensitiveness and is shown in Fig.3 ( degree Fahrenheit ) . It was observed that the electrical opposition of movie lessenings as the concentration of TMA additions, due to the formation of merchandise with an negatron as given by following mechanism [ 19 ] .
( CH3 ) 3N + O2aˆ‘ NO2 + CO2 + H2O + e- ( 3 )
B. Response of detectors towards CO2
Among all the detectors in the array, response of TGS 4161 detector towards assorted concentrations of CO2 is found to be appreciable and is shown in Fig. 3 ( g ) . It has been observed from the response that as the concentration of CO2 increases VRL of detector ‘s measuring circuit has besides been increased. This nature of response is due to the solid electrolytic type of TGS 4161 which maps similar to a battery i.e. , as concentration of CO2 increases VRL of the measuring circuit additions. The feeling component of TGS 4161 consists of cation ( Na+ ) solid electrolyte formed between two electrodes together with a printed warmer ( RuO2 ) substrate. The cathode ( feeling component ) consists of Li carbonate and gold, while the anode ( antagonistic electrode ) is made of gold. When the detector is exposed to CO2 gas, the undermentioned electrochemical reaction occurs [ 20 ] .
Li2CO3 + 2Na+ Na2O + 2Li+ + CO2 ( 4 )
The graduated values of TGS 4161 detector is besides integrated in the embedded database as standard mention to distinguish the healthy milk from mastic milk by observing higher concentration of CO2 during existent clip analysis.
IV. PERFORMANCE VERIFICATION OF DEVELOPED ELECTRONIC NOSE DURING REAL TIME ANALYSIS
To verify the public presentation of the developed electronic olfactory organ, the detector array has been exposed to headspace of milk samples and the response of the detector array has been observed. From the response, it was noted that as clip additions, response of TGS 2620 and TGS 822 detectors was prevailing. Milk which was tested in the present work is from a individual healthy cow without any familial defects and mastic disease, therefore bacterial taint in milk started merely after 7 hours from milking. Based on the response of the detectors and determination devising bids in the expression up tabular array, the developed electronic olfactory organ displayed the spoilage degree through LCD panel, which indicate the presence of ethyl alcohol.
A. Confirmation through rule constituent analysis and gas chromatography
Principle constituent analysis ( PCA ) was performed with detectors in detector array and response of the detector array towards assorted concentrations of VOCs as good existent clip analysis as first and 2nd rule constituent severally, to corroborate the efficiency and effectivity of developed electronic olfactory organ towards natural milk quality favoritism. From the PCA shown in Fig. 4, it is observed that milk after 7th hr falls in the bunch labeled ( ) . This bunch contains VOCs responsible for off spirit in milk due to assorted spoilage factors. The attendant response from PCA confirms the spoilage of milk due to bacterial taint, which is in good understanding with the response of developed embedded based electronic nose as shown in Fig 5. Where, TGS 813 response confirms the presence of ethyl alcohol, which is a good marker for microbial/bacterial taint in natural milk.
The same milk sample was taken in a 5ml phial and gas chromatography was carried out. The consequences confirm the presence of ethyl alcohol which is shown in Fig. 6. Hence the developed electronic olfactory organ with graduated detectors array, conditioning circuit and microcontroller system is found to be efficient in existent clip quality favoritism of milk.
V. VALIDATION OF DEVELOPED PROTOTYPE MODEL
Validation of the developed paradigm theoretical account has been carried out in two stages. In first stage, proof was done by shooting really low concentrations ( 4-10µL of VOC in 30 milliliter of milk ) of VOCs ( ethyl alcohol, ethanal, acetic acid, TMA, DMS, hexanal, etc. , ) straight in to milk, which are responsible for off-flavors during milk spoilage and by observing the same. During this stage, milk samples were collected from local farms and experiments were carried out over a period of 25 yearss repeatedly with the sample from same farm to corroborate the duplicability.
From these surveies, it is observed that the texture of the milk has n’t changed even at higher concentrations ( & A ; gt ; 50ppm ) degrees of, ethanol, TMA, DMS and hexanal. On the other manus at higher concentrations ( & A ; gt ; 50ppm ) of acetic acid and acetaldehyde the texture changed. In the instance of acetic acid, the milk curdled and in the presence of acetaldehyde the coloring material turned to pale pink as shown in Fig.7.
From this observation, it is clearly understood that the presence of lower concentrations ( & A ; lt ; 50 ppm ) of VOCs like ethanal, acetic acid, ethyl alcohol, TMA, DMS and hexanal can non determined from the alteration in coloring material or texture.
In stage two, in order to corroborate the efficiency of the developed paradigm theoretical account in observing the off-flavors generated at initial phase of milk spoilage due to bacterial taint, ageing, mastic disease, familial defect and light harm were studied by roll uping assorted milk samples from local dairy where about 25 lakh litres of milk from the near-by 40 centres were collected daily and processed further before it is being packed for sale at user terminal. In the dairy, the trial performed on a everyday footing are to happen constituents, added H2O, inhibitors, home base cringle count, sediment analysis and bodily cell count. Analysis of milk samples were carried out by trained people through standard methodological analysiss like, chemical trial or by utilizing litmus paper or by heating the sample. All these methods are found to be clip devouring. Besides the truth depends on the trained people. Therefore the developed paradigm theoretical account is employed to find the quality of milk. The experiments were carried out for a period of 2 months repeatedly to corroborate the efficiency and duplicability of the theoretical account with the samples from assorted farms.
The milk quality sensing efficiency of the developed paradigm theoretical account is found to be appreciable compared to the regular trials carried out in the dairy by the experts and trained people.
An RTOS based embedded attack has been carried out with the empanelled detectors TGS 822, 2620, 813, ZnO based chemical detector and 4161, which are calibrated towards assorted concentrations of VOCs ( hexanal, acetic acid, ethanal, dimethyl sulphide, ethyl alcohol, trimethyl aminoalkane ) and CO2 for existent clip quality favoritism. Since the VOCs/gases are major subscriber for off-flavors in the milk and their derived functions, headspace analysis is found be a desirable method for quality favoritism. Therefore, choice favoritism of natural milk was carried out on the footing of database formed with the calibrated information of detectors and fixed threshold bound. The end point embedded electronic olfactory organ was found to be cost effectual, portable and user friendly with important sensitiveness and appreciable selectivity. PCA was carried out to corroborate the efficiency of developed embedded based electronic olfactory organ and the consequences were found to be in good understanding with the developed embedded system. Hence the developed embedded based theoretical account can be efficaciously used for existent clip quality favoritism of milk with significant efficiency.