rapid detection of lard in chocolate and chocolate - based

J. Trop. Agric. and Fd. Sc. 44(2)(2016): 253 – 263

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Article history Received: 26.3.15 Accepted: 9.9.15

Authors’ full names: Saiful Bahri Sa’ari and Yaakob Bin Che Man E-mail: [email protected] ©Malaysian Agricultural Research and Development Institute 2016

Rapid detection of lard in chocolate and chocolate - based food products using fourier transform infrared spectroscopy S. Saiful Bahri1 and Y.B. Che Man2 1Food Science Technology Research Centre, MARDI Headquarters, Persiaran MARDI-UPM, 43400 Serdang, Selangor, Malaysia 2Faculty of Food Science and Technology, Universiti Putra Malaysia, 43400, UPM, Serdang, Selangor, Malaysia

Abstract Fourier transform infrared (FTIR) spectroscopy, in combination with attenuated total reflectance (ATR) and partial least square (PLS) regression was used to detect the addition of lard in chocolate formulation. The spectral bands associated with lard, cocoa butter and their blends (ranging from 0 – 10% of lard in cocoa butter) were recorded, interpreted and identified. A semi-quantitative approach is proposed to measure the percent of lard in blends on the basis of spectral data of the band at the frequency in the region 4000 – 400 cm-1 using the equation y = 1.0144x – 0.0644. The coefficient of determination (R2) was 0.9892 with a standard error of 0.4504. The fingerprints of functional groups in cocoa butter and pure lard enable FTIR spectroscopy to be widely used to authenticate the adulteration in food and pharmaceutical analysis The results showed that FTIR method is versatile, efficient and accurate, and suitable for routine quality control analysis with the result within 2 minutes using sample of less than 2 ml. In this paper, the potential of FTIR spectroscopy as a rapid analytical tool for the quantitative determination of adulterant especially lard in chocolate is demonstrated. Keywords: FTIR, PLS, lard, chocolate and cocoa butter

Introduction Chocolate is one of the most popular snacks and drinks. Chocolate is defined as a homogenous products obtained from a mixture of one or more of the following components; cocoa nib, cocoa mass, cocoa press cake, cocoa powder, with or without addition of cocoa butter and permitted optional ingredients and or flavouring agents (Codex 1981). In Malaysia, the chocolate based food products have been getting positive response from the consumers, thus that many new brand products has the potential to be introduced into the current market. Consumers all over the world are becoming increasingly conscious of the nutritional value and safety of their food and its ingredients. At the same time, there is preference for natural foods and food

ingredients that are believed to be safer, healthier and less subject to hazards than artificial food additives (Farag et al. 1986).

Food adulteration has been found in fats and oils industry for a long time. It is sometime deliberate, sometime accidental. Numerous analytical methods have been used for the analysis of food adulterants such as gas chromatography (GC), high pressure liquid chromatography (HPLC), fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) (Lockley and Bardley 2000; Che man and Marghini 2001). However, some of these methods are too laborious and time consuming. Therefore, an analytical technique which offer rapid and reliable method have to be developed. It is also a

Detection of lard in chocolate using FTIR

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problem when oils are adulterated with lard, either for the purpose of adulteration or new product development, and where the consumption of lard is restricted by religion. Fat adulterants fall into two main categories; vegetable fats and oils and animal body fats. Adulteration with vegetable fats and oils can be detected by several methods such as DSC (Coni et al. 1994), chromatography (Farag et al. 1983), HPLC (Marikkar et al. 2005), electronic nose (Che Man et al. 2005), and DNA-based method (Aida et al. 2007), whilst, animal body fat adulteration is more difficult to detect (Lambelet 1983). Thus, to maintain the market order, regulatory bodies and food processors are urgently need rapid methods of confirming the authenticity of foods.

Presently, the authentication for the adulteration of food ingredients has posed a major challenge for regulatory agencies. This unhealthy practices in food processing has brought the negative impact to the food industry. Labelling of products that shows expensive ingredients are substituted for cheaper ones is common practice in authentication of products (Rohman and Che Man 2011). Lipp and Anklam (1998) have reviewed the literature on the compositional data of vegetable fats used on the proposed as alternatives to cocoa butter in chocolate and confectionary products. Moreover, European Commission allows the addition of vegetable fats other than cocoa butter up to 5% based on finish product (Simoneau 1999).

Hidden ingredients present another serious problem for the Muslim consumers. Chocolate is one of the examples. Foreign fats normally added to chocolate are cocoa butter equivalents (CBE), cocoa butter substitute (CBS) and cocoa butter replacer (CBR) (Simoneau et al. 1999). In analytical field, FTIR spectroscopy has received attention for use in the quantitative analysis of fats and oils (Guillen and Cabo 1997). It is an easy way to identify the presence of

certain functional groups in a molecule. Also, one can use the unique collection of absorption bands to conform the identifying of a pure compound or to detect the presence of specific impurities. It can be utilised to quantify some components of unknown mixture and can be used to analyse liquids, solids, or gases. The fingerprints of functional groups in many compounds enable FTIR spectroscopy to be widely used in food and pharmaceutical analysis (Bittnera et al. 2011).

The application of FTIR in food adulteration has attracted lots of interests in recent years. It is widely used in numerous foodstuff adulteration such as adulterating honey with corn syrup, high fructose corn syrup and inverted sugar (Gallardo-Velazquez et al. 2009); cake formulation (Syahariza et al. 2005) soya bean meal adulterated with melamine (Haughey et al. 2012); virgin coconut oil adulterated with corn and sunflower oils (Rohman and Che Man 2011); edible vegetable oil adulterated with used frying oil (Zhang et al. 2012); extra virgin olive oil adulteration with edible and palm oils (Maggio et al. 2010; Rohman and Che Man 2010).

Kumosinski and Farrell (1993) stated that the application of infrared spectroscopy as spectroscopic techniques is accepted among the most powerful for food analysis since it covers the details on functional group as well as chemical composition that are contained in the infrared spectrum of specific substances. Infrared (IR) spectroscopy as an emergent analytical technique has widely a well-accepted method all over the world. It is environment-friendly and does not demand complicated sample preparation procedure (De Luca et al. 2011).

FTIR was shown to be a fast and reliable method to detect the amount of trans-fatty acid in vegetable fats and oils. It reproducibility was stated to be 0.7% and the accuracy 2.5% with respect to samples

S. Saiful Bahri and Y. B. Che Man

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analysed by chemical methods (Van de voort et al. 1994). FTIR were also used to measure several quality parameters of palm oil and palm oil products such as iodine value (Che Man and Setiowaty 1999), anasidine value (Che Man and Setiowaty 1999a), moisture content (Che Man and Setiowaty 2000) and free fatty acids (Che Man and Setiowaty 1999b). Thus, this present study was undertaken to detect the presence of lard in chocolate and chocolate based food products available in the market and then to develop calibration and validation model for determining the amount of lard added into the products. Materials and methods Extraction of fat from chocolate samples A total of 12 chocolate samples were grounded separately using mortar and pestle. Each sample was labeled to avoid mix-up. All samples were purchased from local supermarket. Using a forceps, samples were put into tissue paper and moulded into a long mould. Then, the tissue paper was inserted into a thimble in the siphon slowly. After that, the siphon including the thimble was placed in the Soxhlet apparatus and then fixed onto the water bath with a conical flask at the bottom to collect the oil for about 8 h. Pure lard preparation Lard sample was extracted by rendering the adipose tissue from various parts of slaughtered pigs, which was obtained from Seri Kembangan, Selangor. The adipose tissue was cut into a small piece enough to fit into small porcelain bowls. The bowls then was placed in oven at 90 – 114 °C. After an hour, oil collected in the bowls was put into a beaker. The bowls were returned into the oven and then oils were collected at several intervals. Anhydrous sodium sulphate was added to the beaker to absorb water from the collected lard.

Standard samples Cocoa butter samples were obtained from Premium Vegetable Oils Sdn. Bhd. as a reference. The calibration set was prepared by spiking lard to cocoa butter in certain ratios covering the range 0 – 15% with intervals at 0.5 g. All blends were prepared on a weight basis to calculate the exact actual percentage of the added fats. The pure fats and the blends were analysed by mean of FTIR spectroscopy. Spectra acquisition The FTIR spectra were obtained with a Perkin-Elmer 1725 series. FTIR spectrophotometer (Perkin Elmer Corporation, Norwalk, Connecticut, USA) equipped with a deurated triglycine sulphate (DTGS) detector and connected to a Perkin-Elmer model 7300 PC operating under infrared data system (IRDM) software. The samples were placed in contact with the ATR Element (ZnSe crystal, 45° ends) at room temperature. FTIR data were collected over the region 4000 – 400 cm-1 by co-adding 32 scans at a resolution of 4 cm-1 with strong apodisation. All spectra were ratioed against a background air spectrum and stored as absorbance values at each data point. All samples were scanned in duplicate. The instrument was maintained with two automatic dehumidifiers to minimise interference by water vapor. Melted drops of each standard were placed on attenuated total reflectance (ATR) and were put in FTIR for scanning. After the sample had been scanned, the ATR were rinsed three times with acetone and dried with a soft tissue before the next sample. Statistical analysis The software program Spectrum QUANT+ version 4.1 (Perkin-Elmer) was used to construct a model of entire samples for calibration development. The adequacy of the calibration was first assessed for the goodness of fit between actual data and FTIR predicted value. All experiments and measurements were performed in duplicate.


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A Partial Least Square (PLS) approach was developed for mathematical treatment of FTIR data. For the PLS equation, the accuracy was assessed based on the smallest standard error (SE) and the highest coefficient of determination (R2) (Miller and Miller 2000). Validation The ‘leave-one-out’ cross validation procedure was used to verify the calibration model. The standard error of prediction (SEP) and R2 were used as the validity criteria for the calibration. The validation step was further investigated using the mean difference (MD) and standard deviation of difference (SDD) for reproducibility and accuracy. Results and discussion A total of 12 samples were used for calibration and validation for PLS quantitative methods in this study. Figure 1 shows the spectra for pure cocoa butter and lard in the frequency range 4,000 – 400 cm-1. The cocoa butter spectrum shows the characteristic absorption bands for common vegetable oils (Safar et al. 1994). These spectra were used as a reference for this study. The absorption of infrared radiation caused a molecule to vibrate. However, the vibrations that were accompanied by a change in the electric dipole moment caused absorption of infrared. The area of FTIR spectrum about 1,400 and 900 cm-1 usually have many peaks, which correspond to complex vibrations of the whole molecule and usually cannot be assigned to any particular vibration. However, the shape of this region is unique for any particular substance and can be used to identify by comparison with a known spectrum. This region is called the fingerprint region. In fats and oils, most of the peaks and shoulders of the spectrum are attributable to specific functional groups (Bendini et al. 2007).

In Figure 1, the spectra illustrates the dominant spectral features associated with fats and oils (Firestone et al. 1992). The spectra of cocoa butter and pure lard samples have very similar absorbance bands in the range of 400 – 4,000 cm−1 (Ripoche and Guillard 2001). CH stretching absorptions in the frequency range of 3,050 – 2,080 cm-1, the carbonyl absorption of triacylglycerol ester linkage at 1,746 – 1,744 cm-1, and the band associated with the fingerprint region (1,500 – 1,000 cm-1). Differences between the raw spectra of cocoa butter and pure lard are observed in five regions: 3,006 – 3,000 cm-1, 1,650 – 1,645 cm-1, 1,380 – 1,360 cm-1, 1,230 – 1,228 cm-1, and 1,119 – 1,096 cm-1 (Guillen and Cabo 1997). These five regions are illustrated in Figure 1 as a, b, c, d and e respectively: 1. Frequency range 3,006 – 3,000 cm-1 (a in

Figure 1). Figure 2 illustrates the differences between the spectra of cocoa butter and pure lard in the frequency range 3,006 – 3,000 cm-1. The lard spectrum (A) has a sharp band at 3,007.09 cm-1, whereas the cocoa butter (E) has a shoulder peak at lower frequency (3,004.73 cm-1) (Lerma-Garcia et al. 2010). Spectra B – D in Figure 2 represents lard/cocoa butter blends containing 0.5 to 10% lard. There were an increased to standard as shown in Figure 3.

2. Frequency range 1,650 – 1,645 cm-1 (b in Figure 1). The C=O group of triglycerides shows a stretching vibration bands at approximately 1,744 cm-1. The

C=C stretching mode of unconjugated olefins usually shows moderate to weak absorption at 1,667 – 1,640 cm-1. Unsubstituted trans-olefin absorb

1,670 cm-1, but the band may be extremely weak or absent; unsubstituted cis-olefins absorb near 1,650 cm-1, and the absorption of this band is stronger than that of trans-olefin. For these reason, these bands can be attributed to


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C=C stretching vibration of disubstituted cis C=C of acyl group of oleic acid and linoleic acid.

3. Frequency range 1,380 – 1,360 cm-1 (c in Figure 1). The bands between

1,400 – 1,000 cm-1 were the most difficult to assign at approximately 1,464 cm-1, all spectra showed the scissoring band of the bending vibration of the methylene group. In all samples near 1,400 cm-1, a small band was observed, which was difficult to assign, also a band at 1,377 cm-1. This could be due to symmetrical bonding vibration of methyl group (Guillen and Cabo 1997; Vlachos et al. 2006.)

4. For frequenc range 1,230 – 1,228 cm-1 (d in Figure 1). In this region, we can see slight changes in the height of the peaks at 1,200 – 1,250 cm-1 frequency region. In general, twisting and wagging vibration of the CH2 groups was observed in the zone between 1,250 – 1,150 cm-1 and these bands were generally resulted from methylene scissoring. This region was most obvious when examined under the naked eyes and known as the fingerprint region for the mixture of lard and chocolate.

5. Frequency range 1119 – 1096 cm-1 (e in Figure 1). In this frequency, pure

lard showed two overlapping peaks having maxima at 1098.69 cm-1 and 1116.88 cm-1. These peaks have been found to be inversely related to the proportion of saturated acyl group and oleic acyl group respectively (Firestone et al. 1992).

Figure 4 showed the spectra of pure lard, cocoa butter and three samples which were done during the experiments. All the samples can be interpreted qualitatively under the naked eyes but for region between 1,700 – 1,000 cm-1 are the most difficult which has known as fingerprint region. Major differences can be seen at 3 regions

which are 1,250 – 1,200 cm-1, 1,070 – 1,130 cm-1 and 1,380 – 1,360 cm-1 with different percentage of lard in pure chocolate.

The presence of peak in this region 1,000 – 1,300 cm-1 showed the presence of C-O bond, which probably comes from alcohols, ethers and esters. This conformed to the fact that the experiments deal to the fats and oils which are esters (Vlachos et al. 2006). PLS calibration and cross validation PLS regression is one of the most widely used calibration models, simple and easy to use, which has proved effective in improving model performance in the presence of linearity (Blanco et al. 2000; Wold et al. 2001).

Figure 5 plots the data from actual data against the PLS FTIR predicted data for lard content in cocoa butter using the none baseline type. This was the best correlation obtained as judged by its R2 = 0.9902 and SE = 0.3978. A good linear regression of the actual data against FTIR predicted data was obtained y = 1.0013x – 0.0344.

After calibrating the model, the validation procedure was carried out to minimise the prediction error and provide an estimate of overall accuracy of the prediction. Figure 6 shows the intercept and slope of linear regression line results of validation of the predictive model for lard content in chocolate by comparing the data obtained by the actual data and FTIR predicted data. This plot is linear with slope of 1.0144 and R2 = 0.9892. The SEP was 0.4504. A good linear regression with the actual data value against FTIR predicted data was obtained y = 0.9751x + 0.1099.

Table 1 compares the data between duplicate FTIR predicted value and the actual values of lard content in term of MD and SDD for overall accuracy (a) and repeatability (r). The term accuracy is defined as the closeness of


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agreement between actual data and the predicted FTIR result. Low MDa (0.0385) and SDDa (0.0573) showed that the FTIR is superior in determining lard adulteration. On the other hand, low MDr (0.1192) and SDDr (0.0592) indicated that the FTIR method has appreciably high repeatability. From this result, it is imperative that FTIR spectroscopy combined with multivariate

calibration of PLS produce the accurate results with low errors for analysis of lard content in chocolate formulations. Other authors have reported that as low as 1% of lard in the mixture with other fats and oils could be detected using FTIR spectroscopy in combination with multivariate calibration of PLS (Che Man and Mirghani 2001; Jaswir et al. 2003; Rohman et al. 2011a).

Figure 1: FTIR spectra of (A) pure lard and (B) cocoa butter. The labeled peaks are absorption bands that are significant in differentiating between cocoa butter and pure lard

Figure 2: FTIR spectra of (A) pure lard, (E) cocoa butter and (B-D) three of cocoa butter/lard blends in range of 0-15%. 1%, 6% and 7% fir B,C and D, respectively


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Figure 3: FTIR spectra of (A) pure lard, (B-D) cocoa butter/lard blends and (E) pure cocoa butter

Figure 4: Spectra of (A) pure lard, (B) cocoa butter and three samples of chocolate or chocolate based food products

Figure 5: Plots of FTIR predicted against actual data value obtained using partial least square regression (PLS)


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Figure 6: Cross validation between FTIR predicted data against actual data

Table 1: Repeatability and accuracy of FTIR prediction of lard content obtained by cross validation

aMD = mean difference; SDD = standard deviation of difference; a = accuracy; r = repeatability Conclusion FTIR Spectroscopy combined with ATR and PLS Regression can be used to determine the lard content when blended in chocolate formulation. The results from this work provide a rapid approach to produce excellent results with a total analysis of less than 2 minutes and require less than 2 ml of samples size. With a low cost and environmental friendly tool for quantitative analysis of adulteration, the study provide basic information about the detection of lard in real chocolates and can be extended to various types of fats normally used in chocolate productions. Furthermore, it is a simpler and faster method with a calibration that can be automated.

Acknowledgement The authors gratefully acknowledge Ms. Syahariza Zainul Abidin for her guidance and also to the laboratory technicians from Faculty of Food Science and Technology, UPM for their assistance in this study. References Aida, A.A., Che Man,Y.B., Raha, A.R. and Son, R.

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Statistic Actual Data PLS FTIR

MDa 0.038487

SDDa 0.057331

MDr 0.119247

SDDr 0.059167


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Abstrak Spektroskopi inframerah ‘fourier transform’ (FTIR) dengan kombinasi ‘attenuated total reflectance’ dan ‘partial least square’ (PLS) telah digunakan untuk mengesan penambahan lemak babi di dalam formulasi coklat. Jalur-jalur spektrum yang bergabung dengan lemak babi, lemak koko dan campuran kedua-duanya (julat dari 0 – 10% lemak babi di dalam lemak koko) telah direkod, dianalisis dan dikenal pasti. Pendekatan semi kuantitatif telah diperkenalkan untuk mengira peratusan lemak babi di dalam campuran pada nilai asas jalur frekuensi bergerak di dalam kawasan 4,000 – 400 cm-1, menggunakan persamaan y = 1.0144x – 0.0644. Koeffisi pekali penentuan (R2) adalah 0.9892 dengan ramalan ralat biasa (SE) ialah 0.4504. 'Fingerprint' kumpulan berfungsi pada koko dan lemak babi membolehkan spektroskopi inframerah digunakan secara meluas untuk mengesahkan kehadiran penambahan lemak babi di dalam produk makanan dan farmaseutikal. Keputusan yang telah diperoleh menunjukkan kaedah FTIR ialah umum, berkesan dan tepat serta sesuai untuk analisis pengawalan mutu biasa dengan keputusan yang diperolehi di dalam masa 2 minit dan sampel yang tidak melebihi 2 ml. Dalam penyelidikan ini, potensi spektroskopi FTIR sebagai alat analisis yang cepat untuk penentuan kuantitatif kepada pencampuran terutamanya lemak babi di dalam coklat telah ditunjukkan.

rapid detection of lard in chocolate and chocolate - based

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