Authentication of Palmyrah Palm Jaggery

A Preliminary Study and Principal Component Analysis for the Authentication of Palmyrah Palm Jaggery Using NIR Spectroscopy

• Selvaratnam Balaranjan, Kugamoorthy Velauthamurty, Ganeshalingam Sashikesh

Abstract.

Palmyrah jaggery is used as a popular traditional sweetener in Jaffna peninsula, Sri Lanka. It is a nutrient rich crude sugar which is also used in the traditional medicine. The authenticity of the product in markets is questionable since there is no analytical methods exist to detect adulterations. In this study, NIR spectroscopy with principal component analysis is used for the authentication of jaggery and identification of the adulterant. Jaggery was produced in laboratory as pure and adulterated with sugar and rice bran at different concentrations. Aqueous solutions of these samples were prepared and used to obtain NIR spectra. Principal component analysis of the spectra was found useful in identifying the adulterations and for the authentication of jaggery.

Key words: Palmyrah, jiggery, adulterations, sweetener, NIR spectroscopy.

1. Introduction

Palmyrah palm Borassus flabellifer is a celestial tree which is abundant in the northern part of Sri Lanka. Other than northern Sri Lanka, it is widespread in the arid tropics of South America, East Africa, India and South-East Asia. Palmyrah palms are economically useful: leaves are used for thatching, mats, hats, etc.., stalks are used to make fence, black timber used in constructions, young plants, fruits, jelly like seeds are consumed as foods. A sugary liquid oozed from the inflorescence of palmyrah pam, called sap, can be obtained from the young inflorescence of either male or female ones. The sap is a sweet clear watery liquid and contains sugars, vitamins and minerals. Also fresh sap is a good source of vitamin B complex[1]. The sap can be consumed directly. Further, there are several products can be made by processing the sap: jaggery, treacle, sugar candy, toddy, vinegar, arrack and wine.

1. Jaggery

Jaggery is a main product made out of sap in Sri Lanka. jaggery is much more nutritious than crude cane sugar, containing 1.04 % protein, 0.19 % fat, 76.86 % sucrose, 1.66 % glucose, 3.15 % total minerals, 0.861 % calcium, 0.052 % phosphorus; Also 11.01 mg iron per 100 g and 0.767 mg of copper per 100 g. It contains vitamins as well: analysis on jaggery from has shown the presence of vitamins such as riboflavin, 402 mg/100 g, vitamin B₁₂, 15 mg/100 g, vitamin C, Thiamine and nicotinic acid[1]. jaggery is used as a popular traditional sweetener in northern Sri Lanka and India. Furthermore, jaggery posses medicinal properties: it is used in indigenous medicine [2], also it is reported that jaggery posses antitoxic and anti-carcinogenic properties as well[3]. Traditionally palmyrah jaggery has high demand among the occupants of northern Sri Lanka. This can be attributed to the use of jaggery as a traditional sweetener and it use in indigenous medicine. jaggery is expensive relative to commercial white crystalline sugar: as of writing, 1 Kg of jaggery costs around 600 LKR which is roughly six times that of commercial white crystalline sugar. Due to its relative high price and popularity, Jaggery is often adulterated with cheap adulterants such as cane or beet sugar, rice bran, corn flour, etc. A study by ITI reveals that the ratio between reducing sugar is to non-reducing sugars can be used as a measure to identify the adulterations in the kithul jaggery[4]. However there are no reported works on the authentication of palmyrah jaggery.

2. Food Adulterations

Adulteration is the practice of adding low-value substances to a relatively high value food in order to increase the financial return. It is often unlikely for consumers and food processors to detect the adulterations without special chemical or physical analysis. But it is a fraudulent practice. There are several cases of adulterations: sugars in honey [5], proteins in yogurt [6], etc. Adulteration has several consequences such as decrease in the demand, unwanted health effects, unfair competition and so on.

The adulterants are often have same chemical composition for example, honey is rich in sugars such as sucrose glucose and fructose and is adulterated with high fructose corn syrups[7], jaggery syrup, sugar solutions etc., extra-virgin oil with different edible oils[8], olive oil with soya oil, sunflower oil, corn oil walnut oil and hazelnut oil[9], yogurt with vegetable protein powder, edible gelatin, and even industrial gelatin[6] etc. Since the chemical composition is similar, the detection of adulteration is difficult. Nevertheless, there are several methods exists to detect and characterize the adulterations. These detection processes have different approaches for the authentication process: determining the ratio between some chemical compositions for authentic samples and compare the ratio for the test samples with the assumption that the ratios are constant for a particular type of food, search for specific markers present in the adulterants. Highly-sophisticated analytical techniques such as GC-MS, HPLC, GC, IR-MS, NMR and DNA based techniques are used in the authentication process. Although these methods provide desirable solution to the problem, they are usually time consuming, require dedicated laboratories equipped with costly instruments and require highly-skilled personnel to do the analysis. However, in contrast to those methods, infrared spectroscopy, specifically mid-infrared (MIR) and near-infrared (NIR) spectroscopic methods used to address this problem because of its desirable characteristics such as minimal or no sample preparation, short analysis time, does not require chemical reagent purchase or disposal, relatively cost effective and easy deployment once initial method is developed.

3. NIR Spectroscopy

NIR Spectroscopy operates in 750-2500 nm (12500 – 4000 cm^-1) region of electromagnetic spectrum. This is a vibrational spectroscopic technique, shares the same fundamental principle as that of Mid-IR (4000 – 200 cm^-1). However, opposed to fundamental vibrations which arise in the MIR, NIR give rise to overtones and combinations of fundamental vibrations, also the NIR absorption bands overlap with each other. This renders the NIR spectrum more complex than the IR spectrum and hence the chemical information from NIR spectra is poorly resolved. In NIR asymmetric vibrations takes place such as C-H, N-H and O-H this makes NIR spectroscopy useful in the studies of products of biological origin.

4. Chemometrics

To resolve useful information from NIR spectra, it is necessary to utilize multivariate statistical analysis. The use of multivariate statistical techniques in the analytical chemistry is termed as chemometrics. Chemometric techniques can be used for qualitative and quantitative studies. These techniques analyze the correlations between variables, since absorptions in NIR wavelengths are correlated with each other chemometrics is exploited in NIR analysis.

Principal Component Analysis

Principle Component Analysis (PCA) is a chemometric technique which can be used to reduce the number of variables when the systems (samples) are characterized by several variables (absorption at different wavelengths). This is a variable reduction technique and analyzes correlation between variables, reduce the noise and combine the variables into artificial variables called Principle Components (PCs) which explains the most variation among the samples. PCA can be used to study the characteristics of different samples and different groups of samples by analyzing the absorptions at certain wavelength regions which accounts for the similarity/dissimilarity among the samples.

2. Materials and Methods

Sap was collected around 09 30 a.m. in weekdays from a sap based production facility in Chavakacheri and Jaffna. After brought to laboratory, the sap was de-limed and neutralized by the addition of concentrated phosphoric acid. Then de-limed the sap was used to prepare jaggery as pure and adulterated forms as in Table 1.

Table 1 Composition of jaggery samples produced for the analysis.

Sample Preparation

Jaggery was dried in an oven at 102 °C for two hours to remove moisture. Then 5.00 g of sample was added into 20 ml of distilled water and the mixture was stirred at 1000 rpm for five minutes using magnetic stirrer. Then the above solutions were used to obtain the NIR spectra.

NIR Spectrum

The spectra were obtained at room temperature in Jasco V-570 UV/VIS/NIR spectrometer in the range of 750 to 1300 nm in transmittance mode. Each of the spectra is an average of three individual spectrums. The obtained spectra were exported as ASCII files using the Spectra Manager v 1.5 (Jasco Inc) and imported into Unscrambler X (version 10.1, Camo ASA, Oslo, Norway) for PCA analysis.

PCA analysis

All the spectra were baseline corrected prior to analysis. The PCA analysis was done for the mean-centered data using Non-linear Iterative Partial Least Squares algorithm with equal weight for all variables, full cross validation was done.

3. Results and Discussion
   1. NIR Spectrum

Fig. 1. NIR Transmission Spectra of Samples: Solid line – pure, dashed line – samples adulterated with sugar and dotted line – samples adulterated with rice bran.

The NIR spectra of eight samples are shown in Fig. 1. Changes in the absorption intensities are visible in the wavelength ranges 900-1000 nm and 1100-1200 nm. N-H 2^nd overtone, O-H 2^nd overtone and C-H 3^rd overtones occur in the 900-1000 nm region. C-H 2^nd overtones and O-H combinations occur in the 1100-1200 nm regions.

2. PCA Analysis

Fig. 2. PC-1 versus PC-2 for Baseline Corrected Spectra

Fig. 3. PC-1 versus PC-2 Scores for Savitzky-Golay 1^st Derivative Spectra

Fig. 4. PC-1 versus PC-3 Scores for Savitzky-Golay 1^st Derivative Spectra

In the PCA analysis of baseline corrected spectrum, Fig. 1, PC-1 accounts for 99 % of variation and PC-2 accounts for 1 %. Here only PC-1 is the optimum component. For the PCA analysis of Savitzky-Golay 1^st derivative spectra, three PCs were extracted with PC-1, PC-2 and PC-3 accounting 95 %, 2 % and 1 % of variations respectively. Further, score plot of PC-1 versus PC-3 (Fig. 2) separates the three types better than the PC-1 versus PC-2 score plot (Fig. 3). Based on the PCA analysis of samples, three different groups of samples can be identified: I-pure, II-samples adulterated with sugar and III-samples adulterated with rice bran. In the score plot of PC-1 versus PC-2 of baseline corrected spectra, samples which were adulterated with rice bran can easily distinguished from the pure and those adulterated with sugar. PC-1 versus PC-3 plot of the Savitzky-Golay 1^st derivative spectra also gives good clustering between the three groups.

4. Conclusion

From this initial study we can conclude that PCA analysis of NIR spectral data is useful in the authentication of palmyrah jaggery, also the type of adulterant can be determined..

5. References

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