Engineering, Technology & Applied Science Research Vol. 11, No. 3, 2021, 7111-7117 7111 www.etasr.com Kamil et al.: Investigating the Quality of Milk with Spectroscopy and Scattering Theory Investigating the Quality of Milk using Spectrometry Technique and Scattering Theory Nur Ain Insyirah Muhamad Kamil Advanced Devices and System (ADS) Faculty of Engineering and Built Environment Universiti Sains Islam Malaysia Negeri Sembilan, Malaysia Wan Zakiah Wan Ismail Advanced Devices and System (ADS) Faculty of Engineering and Built Environment Universiti Sains Islam Malaysia Negeri Sembilan, Malaysia Juliza Jamaludin Advanced Devices and System (ADS) Faculty of Engineering and Built Environment Universiti Sains Islam Malaysia Negeri Sembilan, Malaysia Zatunnur Syakirah Nor’aini Advanced Devices and System (ADS) Faculty of Engineering and Built Environment Universiti Sains Islam Malaysia Negeri Sembilan, Malaysia Sharma Rao Balakrishnan Advanced Devices and System (ADS) Faculty of Engineering and Built Environment Universiti Sains Islam Malaysia Negeri Sembilan, Malaysia Irneza Ismail Advanced Devices and System (ADS) Faculty of Engineering and Built Environment Universiti Sains Islam Malaysia Negeri Sembilan, Malaysia Musab Sahrim Advanced Devices and System (ADS) Faculty of Engineering and Built Environment Universiti Sains Islam Malaysia Negeri Sembilan, Malaysia Abstract-Milk is a dairy product that contains dissolved proteins, carbohydrates, fat, and many minerals. Milk enhances body growth and provides vital energy and fatty acids. Milk can turn bad after being kept at room temperature for several days. The endurance of milk could depend on its fat and protein composition. Our work aims to compare the quality of milk after being kept at room temperature for several days using spectroscopy methods. Modeling based on scattering theory is also provided to compare the light propagation in milk, water, and air. A VIS-NIR spectrometer was used to observe the light absorption, transmission, and reflectance whereas a modeling approach was applied to study the scattering, absorption, and extinction efficiencies. The milk samples consist of full cream milk kept at room temperature for 8 days, 11 days, 14 days, and 17 days. The results show that milk without fermentation has higher light absorbance and lower transmission compared to milk with fermentation, due to changes in milk composition after the fermentation process. Milk scatters more light compared to water and air due to its fat globule and protein ingredients. The output of this study can be used as a reference for studies involving bacteria or microorganisms in milk. It also can be used to compare the quality of milk with and without air exposure. Keywords-light propagation; absorbance; transmittance; reflectance; scattering; milk; spectroscopy I. INTRODUCTION It is crucial to monitor the quality of milk in order to ensure we gain sufficient nutrients and minerals and prevent the occurrence of diseases. Cow milk consists of water (87%), fat (4%), proteins (3.4%), lactose (4.8%), and minerals (0.8%) [1]. Fat composition is not similar in full cream milk and skimmed milk. A layer of cream forms on the milk’s surface if it is exposed for several days. This cream consists of spheres of various sizes floating in milk surrounded by a fat globule membrane. The membrane is responsible for fat protection against enzymes and prevents any globule coalescing into butter grains [1]. The spectroscopy technique can be used to observe the optical properties of milk based on light absorbance, transmission and scattering. Mie scattering theory is used to compute the absorption coefficient (μ ), the scattering coefficient (μ ), and the phase function p(θ), where θ is the scattering angle [2]. Mie theory is used to calculate the spectral dependence for the extinction cross section of nanoparticle suspensions [3]. The pump source energy passes Corresponding author: Wan Zakiah Wan Ismail (drwanzakiah@usim.edu.my) Engineering, Technology & Applied Science Research Vol. 11, No. 3, 2021, 7111-7117 7112 www.etasr.com Kamil et al.: Investigating the Quality of Milk with Spectroscopy and Scattering Theory through the turbid media depending on optical properties such as the refractive index, scattering, anisotropic factor, and laser light absorption [4]. The optical properties of milk based on backscattering intensity can be used to study fat and protein concentrations [5]. The complex fluid of milk is made up of many components such as water, lipids, lactose and protein [6, 8]. Spectroscopy is widely used to measure the optical properties of samples based on light propagation and fluorescence. Color spectroscopy is used to obtain information about the atoms and molecules [8-9]. The absorbance spectroscopy is a technique used to measure the amount of absorbed light [10, 11] with the determination of solution concentration based on Beer’s Law [12]. NIR spectrometer and VIS-NIR spectrometer with different wavelength ranges are used to determine the accuracy of the intensity spectrum in the spectroscopy analysis [13]. Many recent studies on light propagation in milk involve backscattering [5], external cavity-quantum cascade laser spectroscopy [6], and laser diffraction and centrifugation [7]. Authors in [8] introduced the simplified NIR spectroscopy in measuring the end of milk fermentation by transforming sugar to lactic acid. The key characteristic of the fermentation process is the pH end point value, in the range of 4.4-4.5 [8]. This technique is quite complicated and costly. To the best of our knowledge, no comparison has been conducted using milk after several days’ exposure and water. The previous studies also do not provide a modeling approach on light scattering in milk. Our previous work [14] compared the optical properties of full cream and skimmed milk using different spectrometer types. We found that full cream milk has higher absorption due to its higher fat content. This research is continued in the current paper, which aims to study the light propagation in various milk samples for different exposure at room temperature durations based on spectroscopy techniques using Visible (VIS) and Near Infra-Red (NIR) spectrometers. The technique is simpler and cheaper than the ones used in previous studies as indicated in the experimental section. The output shows that the newly opened milk sample absorbs more light than the other samples. A modeling approach based on Mie theory was also provided to compare light scattering in milk, water, and air. II. THEORETICAL FRAMEWORK For the computation of Mie efficiencies, there are two input parameters which are the complex refractive index m and the parameter size x as shown in (1) and (2) [12]. = ’ + " (1) = = (2) where ’ is the real refractive index, " is the imaginary refractive index, is wave number in the ambient medium, and is the sphere radius. The key parameters of Mie theory are the computed amplitudes of the scattered field. The coefficients and are required to obtain the Mie efficiency using Spherical Bessel function n (n=1, 2, …) of higher order and work well in the wider range of size parameters [15]. The efficiency of extinction and scattering can be identified in forward-scattering theorem and in the integration of the power scatters in all directions. The absorption efficiency can be identified with the equation of energy conservation [16]. Meanwhile, the backscattering efficiency is applicable to monostatic radar [15]. Equations for absorption, scattering and backscattering efficiency are: = ∑ (2 + 1) ( + ) (3) = ∑ (2 + 1)(| | + | | ) (4) = + (5) = |∑ (2 + 1)(−1) ( − )| (6) where x is the parameter size and n is the spherical Bessel function order n. The efficiency of radiation pressure can be proven by the Two-Stream Model and correlates with the asymmetry parameter [17]. = + ( ) (7) where is the scattering angle. Amplitude functions 1 and 2 indicate the scattering properties or the scattering of an electromagnetic wave from a spherical particle. The scattering function is required for the far field scatterer [16]: ( ) = ∑ ( ) ( + ) (8) ( ) = ∑ ( )( + ) (9) where = 2 −1−1 . −1 − −1 −2 = . − ( + 1) III. METHODOLODGY The research is conducted using experimental and theoretical methods. The light absorption and scattering analysis in milk are based on Mie scattering theory. The scattering, absorption, extinction, and backscattering efficiencies are analyzed in a homogeneous dielectric sphere and its angular scattering using MATLAB. The analysis is also repeated for water and air. A. Modeling Approach The modelling part is used to determine the characteristics of light in a disordered medium using MATLAB. The light propagation efficiency with the justification of Mie coefficient matrix is computed. The angular functions are also computed to produce the Mie angular efficiency. Figure 1 shows the flowchart of the constructed modeling approach. B. spe pro to dif yo flo 14 of pla Engineerin www.etasr Fig. 1. Experimenta The Ocean O ectrometer we opagation in m ensure the acc fferent days o gurt after 14 owchart of the Fig The milk sam , and 17 days. milk and wa aced in a cuve ng, Technology r.com The flowchar al Approach Optic Flame ere used to ob milk. Every ex curacy of the o of exposure w days of air experimental g. 2. The flow mples were ke The samples ater respective ette of 10mm y & Applied Sci rt of the modeling NIR spectrom bserve the cha xperiment was output. Five sa were used (th exposure). F method. wchart of the expe ept at room tem were diluted w ely. The prep m and shaken l ience Research Kamil et g approach. meter and VIS aracteristics of s repeated 10 amples of milk he sample tur Figure 2 show eriment. mperature for with a ratio of pared samples lightly. 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Figure 4 Milk sample samples after les observed. experimental set- d full cream milk s (from right to le r reflectance s ransmission sp es and solids. ctance intensi laced on the ample in the c e transmits the aced on the observed by tes inside the m V. RESULTS orks [5, 6] h of milk Authors in [7 ntrol the deve authors in [8] tion automatio which is kept scopy. We do 7 Spectroscopy an older and was ). The light fro spectrometer d on a compute 4 shows the mi es of 8 and 14 days becam -up for the spectr k samples after d eft) of exposure. spectroscopy is pectroscopy se NIR spectrom ity spectrum o stage RTL-T cuvette was o e light from the stage RTL-T using a NIR medium. S AND DISCUSS have analyzed through ba 7] studied th elopment of th used NIR spe on. In this pa at room temp o a simple mo 7113 nd Scattering T s illuminated om the cuvette (Figure 3). er screen usin ilk samples us 11 days were me transparent ometry technique dilution with wate s different from etup. It can be meter was us of the samples T. The reflec observed by a e halogen ligh T. The reflec spectrometer w SION d fat and pr ackscattering he homogeniz he cream laye ectroscopy to aper, we study perature using odeling to com Theory by a e was The ng the sed in e still t with e. er after m the e used ed to . The ctance fiber ht and ctance when rotein and zation er on study y the g VIS mpare Engineering, Technology & Applied Science Research Vol. 11, No. 3, 2021, 7111-7117 7114 www.etasr.com Kamil et al.: Investigating the Quality of Milk with Spectroscopy and Scattering Theory the light propagation in milk, water and air. The modeling analysis uses Mie theory to compute the efficiency of scattering, absorption, extinction, backscattering, asymmetry parameter, and radiation pressure whereas the experimental section shows the output in terms of absorbance, transmission, and reflectance. The output from the theoretical and experimental study are analyzed and discussed thoroughly in this section. A. Modeling based on Mie Scattering Theory The measurements of scattering, extinction and absorption efficiency based on Mie theory were conducted in MATLAB. The input parameters were the complex refractive index and the parameter size x [18]. Modeling was done for milk, water, and air. Figures 5 and 6 summarize the modeling results. (a) (b) (c) Fig. 5. Mie theory based efficiencies for (a) milk, (b)water, and (c) air. Equations (3) to (7) were used in Figure 5. Figure 6 is plotted based on (8)-(9). The extinction, forward scattering, absorption, and backscattering efficiencies are represented by Qext, Qsca, Qabs and Qb respectively. Figure 5 shows clearly that milk has better scattering efficiency than water and air. At parameter size 2, the scattering efficiency in milk (Figure 5(a)) reaches 0.6, while the scattering efficiency in water (Figure 5(b)) and air (Figure 5(c)) are 0.7 and 5×10-7 respectively, prooving that the least light scattering occurs in the air, whereas milk and water consist of particles which can scatter the light. We presume that the light scattering and absorption are affected by the size and concentration of the particles, the incident light wavelength, and sample size [19]. Milk depicts the highest efficiency of light absorption due to its composition of fat globules and proteins. Figure 5 also shows that the forward scattering is more efficient compared to the backscattering for all samples due to the larger particles size of the samples. Figure 6 shows the scattering angle of milk, water and air respectively. (a) (b) (c) Fig. 6. Angular scattering for (a) milk, (b) water, and (c) air. We observe that milk has larger value of angular scattering than water and air. It is clearly shown that milk has higher scattering effect. We attribute that to the milk contents which mostly consist of fat and proteins which can scatter light [20]. B. the sam tem an wa res ref Fig sam sam the hig 17 to Engineerin www.etasr Experimenta The spectra o e samples w mples of fre mperature for NIR Spectr avelength ran spectively. Fig flectance spect (a) (b) (c) g. 7. (a) Abso mples for various Figure 7(a) mples for diffe e absorbance gher than the m days. The abs high attenuati ng, Technology r.com al Results of reflectance, were monitore esh full-crea 8, 11, 14, and rometer and nges of 950nm gure 7 depicts tra of the milk orbance, (b) trans days of fermentat shows the ab ferent days of spectra in fre milk that has b sorbance of m ion coefficient y & Applied Sci , transmission ed with the m milk we 17 days. The a VIS-NIR m-1650nm an the absorbanc k samples. smission, and (c) tion. bsorbance spe exposure. It is eshly opened been kept at ro milk reaches its t which quick ience Research Kamil et n, and absorban spectrometer. re kept at experiment ut Spectrometer nd 350nm-10 ce, transmissio reflectance of th ectrum of the s clearly show full-cream m oom temperatu s peak at 700nm kly absorbs the h V t al.: Investigat nce of . The room tilized with 000nm on and he milk e milk wn that milk is ure for m due e light arou tem agg [21 mil dec Fig. open ope mil ligh than dur ferm ferm as t Vol. 11, No. 3, 2 ting the Quality und 700nm. mperature, they gregate and cr ] (see Figure 4 lk is gradual creases due to (a) (b) (c) 8. (a) Absor ned milk sample, Figure 7(b) ened and ferm lk has lower li ht transmissio n in the rest of ring the coagul mentation pro mented milk e the lactic acid 2021, 7111-711 y of Milk with S When milk y undergo phy reate lumpy w 4). Hence, the lly decreasing milk coagulati rbance, (b) trans water, and milk s shows the t mented milks. ight transmissi on in fermente f the samples a lation [21, 22] ocess which p experiences de bacteria grow 7 Spectroscopy an k samples ar ysical changes which affect th e quality from g as the pro ion [22]. smission, and (c) sample after 17 da transmission s . The newly ion than the fe ed milk after as the particle ]. The protein produces lact ecay and the p w to produce th 7115 nd Scattering T re kept at where the par he light absor fresh to ferm otein concentr ) reflectance of ays. spectra of fr opened full-c ermented milk 17 days is h s in milk aggr thickens due t tic acid [23]. pH level decr he acid [24]. Theory room rticles rption mented ration newly reshly cream k. The higher regate to the The reases Engineering, Technology & Applied Science Research Vol. 11, No. 3, 2021, 7111-7117 7116 www.etasr.com Kamil et al.: Investigating the Quality of Milk with Spectroscopy and Scattering Theory Figure 7(c) shows the reflectance spectra of the milk samples. The reflectance of newly opened milk is higher than the fermented milk's. The low reflectance values for fermented milk are recorded due to its high water absorption [25]. Hence, we suppose that the presence of fat globules and protein micelles in milk affect the light reflectance. The reflectance intensity decreases over the fermentation process due to the changes of protein and fat globules [26]. Figure 8 shows the spectra comparison of milk samples and water. Figure 8(a) shows that water absorbs most of the light at 600nm whereas the absorption peak of milk is at 700nm. Milk and water depict similar transmission peaks at ~ 650nm (Figure 8(b)). Water sample shows higher transmission spectrum as it is more transparent than milk. Newly opened milk samples have higher reflectance than water due to their fat and protein composition. The size and shape of particles, the composition, and the concentration of the tested samples can affect the absorption, transmission, and reflectance of the samples respectively [26]. Newly opened milk samples consist of various particle compositions whereas the fermented milk samples have experienced physical state changes. V. CONCLUSION In conclusion, this research investigates the quality of milk for samples freshly opened and after being kept at room temperature for several days using spectroscopy and scattering theory. The optical properties of milk samples were investigated using VIS and NIR spectrometers. Newly opened milk samples have higher light absorbance and lower light transmission compared to the fermented milk, due to the aggregation of the fat and protein particles in milk during the fermentation process. Besides that, modeling based on scattering theory was done to compare the light propagation in milk, water, and air. The modeling shows that milk scatters more light compared to water and air due to the presence of fat globule, protein, and minerals. The outcome of the study shows that the quality of milk is reduced when it is kept at room temperature for several days. This is proved by both naked eye observation and spectroscopy. The outcome of this study can be useful in supporting future analysis studies on dairy products. ACKNOWLEDGEMENT We acknowledge the support of the Ministry of Education of Malaysia under the FRGS grant (FRGS/1/2018/STG02/ USIM/02/2) and Universiti Sains Islam Malaysia (USIM) for the funding and support. REFERENCES [1] G. H. Schmidt, L. D. V. 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