Quantitative analysis of alcohol, sugar, and tartaric Acid in alcoholic beverages using attenuated total reflectance spectroscopy

A Sensor-Based Methodology to Differentiate Pure and Mixed White Tequilas Based on Fused Infrared Spectra and Multivariate Data Treatment

Mexican Tequila is one of the most demanded import spirits in Europe. Its fast-raising worldwide request makes counterfeiting a profitable activity affecting both consumers and legal distillers. In this paper, a sensor-based methodology based on a combination of infrared measurements (IR) and multivariate data analysis (MVA) is presented. The case study is about differentiating two categories of white Tequila: pure Tequila (or ‘100% agave’) and mixed Tequila (or simply, Tequila). The IR spectra were treated and fused with a low-level approach. Exploratory data analysis was performed using PCA and partial least squares (PLS), whilst the authentication analyses were carried out with PLS-discriminant analysis (DA) and soft independent modeling for class analogy (SIMCA) models. Results demonstrated that data fusion of IR spectra enhanced the outcomes of the authentication models capable of differentiating pure from mixed Tequilas. In fact, PLS-DA presented the best results which correctly classified all fifteen commercial validation samples. The methodology thus presented is fast, cheap, and of simple application in the Tequila industry.

Application of FTIR-ATR to discriminate peach nectars with higher and lower sugar contents

Abstract Fruit juice does not have the same nutritional value as fresh fruit with regards to the vitamin, mineral and dietary fibre contents and the antioxidant properties. However, it can be part of a healthy diet if it is produced with the minimal addition of sugar. This study aimed to evaluate the performance of the FTIR-ATR technique to discriminate the authenticity (concerning the addition of other pulps) and amount of sugar in peach nectars. This technique is usually used in food analysis because it does not require sample preparation, is quick and allows for the determination of several parameters with a single sample aliquot. The nutritional information provided on the labels of 69 samples of 23 different brands of commercial peach juice, was analysed. The differences in the nutritional composition and in the ingredients were determined according to an analysis of the labels. The largest differences observed between the samples were the sugar contents, the percentages of pulp and the addition of other pulps. All samples were analysed by FTIR-ATR equipped with a controlled temperature flow-through cell. The spectral multivariate analysis suggested it was possible to identify differences in the amount of sugar present and identify the presence of fruit pulps other than peach.

Hybrid organic-inorganic coatings via electron transfer behaviour

A novel method to functionalize the surface of inorganic coating by growing organic coating has been investigated based on microstructural interpretation, electrochemical assessment, and quantum chemical analysis. For this purpose, inorganic coating with magnesium aluminate, magnesium oxide, and titanium dioxide was prepared on magnesium alloy via plasma electrolytic oxidation (PEO), and, then, subsequent dip-coating method was used to tailor organic coating using diethyl-5-hydroxyisophthalate (DEIP) as organic molecules. The incorporation of TiO₂ particles worked as a sealing agent to block the micro-defects which resulted mainly from the intense plasma sparks during PEO. In addition, such incorporation played an important role in enhancing the adhesion between inorganic and organic coatings. The use of DEIP as organic corrosion inhibitor resulted in a significant decrease in porosity of inorganic coating. Quantum chemical calculation was used to clarify the corrosion inhibition mechanism which was activated by introduction of DEIP. Thus, the electrochemical analysis based on potentiodynamic polarization and impedance spectroscopy tests in 3.5 wt% NaCl solution suggested that corrosion resistance of magnesium alloy sample was enhanced significantly due to a synergistic effect arising from the hybrid inorganic and organic coatings. This phenomenon was explained in relation to electron transfer behaviour between inorganic and organic coatings.

Non-destructive determination of ethanol levels in fermented alcoholic beverages using Fourier transform mid-infrared spectroscopy

BACKGROUND

Traditional fermented alcoholic beverages are indigenous to a particular area and are prepared by the local people using an age-old techniques and locally available raw materials. The main objective of this work was the direct determination of ethanol in traditional fermented alcoholic beverages using mid infrared spectroscopy with partial least squares regression, verifying the robustness of the calibration models and to assess the quality of beverages.

RESULTS

The level of ethanol determination in Ethiopian traditional fermented alcoholic beverages was done using mid infrared spectroscopy with partial least squares regression (MIR-PLS). The calibration and validation sets, and real samples spectra were collected with 32 scans from 850-1200 cm-1. A total of 25 synthetic standards (calibration and validation sets) with ethanol (2-10% w/w) and sugars (glucose, fructose, sucrose and maltose) (0-5% w/w) compositions were used to construct and validate the models. Twenty-five different calibration models were validated by cross-validation approach with 25 left out standards. A large number of pre-treatments were verified, but the best pre-treatment was subtracting minimum + 2nd derivative. The model was found to have the highest coefficients of determination for calibration and cross-validation (0.999, 0.999) and root mean square error of prediction [0.1% (w/w)]. For practical relevance, the MIR-PLS predicted values were compared against the values determined by gas chromatography. The predicted values of the model were found to be in excellent agreement with gas chromatographic measurements. In addition, recovery test was conducted with spiking 2.4-6.4% (w/w) ethanol. Based on the obtained recovery percentage, 85.4-107% (w/w), the matrix effects of the samples were not considerable.

CONCLUSION

The proposed technique, MIR-PLS at 1200-850 cm-1 spectral region was found appropriate to quantify ethanol in fermented alcoholic beverages. Among the studied beverages (Tella, Netch Tella, Filter Tella, Korefe, Keribo, Borde and Birz), the average ethanol contents ranged from 0.77-9.1% (v/v). Tej was found to have the highest ethanol content whereas Keribo had the least ethanol content. The developed method was simple, fast, precise and accurate. Moreover, no sample preparation was required at all. However, it should be noted that the present procedure is probably not usable for regulatory purposes (e.g. controlling labelling).

Synergistic effect of tartaric acid with 2,6-diaminopyridine on the corrosion inhibition of mild steel in 0.5 M HCl

The inhibitive ability of 2,6-diaminopyridine, tartaric acid and their synergistic effect towards mild steel corrosion in 0.5 M HCl solution was evaluated at various concentrations using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS), and weight loss experiments. Corresponding surfaces of mild steel were examined by atomic force microscope (AFM), field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) analysis. The experimental results are in good agreement and reveal a favorable synergistic effect of 2,6-diaminopyridine with tartaric acid, which could protect mild steel from corrosion effectively. Besides, quantum chemical calculations and Monte Carlo simulation were used to clarify the inhibition mechanism of the synergistic effect.

Determination of Alcohol Content in Alcoholic Beverages Using 45 MHz Benchtop NMR Spectrometer

Alcohol or ethanol is considered the most widely used recreational drug worldwide, and its production, consumption, and sale are strictly regulated by laws. Alcohol content of alcoholic beverages (wine, beers, and spirits) is about 3–50% v/v. Analytical methods to determine the alcohol content must be reliable, precise, and accurate. In this study, the amount of ethanol in several alcoholic beverages was determined using a 45 MHz low-field benchtop NMR (nuclear magnetic resonance) spectrometer. Internal standard and standard addition analytical methods were utilized to quantify ethanol. For both methods, acetic acid or acetonitrile was used as internal standard to quantify alcohol content by using the peak area corresponding to the methyl peaks of ethanol, acetic acid, or acetonitrile. Results showed that internal standard method gave values of percent alcohol that are in close agreement with the indicated label as confirmed by running the samples in a 400 MHz high-field NMR spectrometer using acetic acid as internal standard. This study demonstrates the utility of a benchtop NMR spectrometer that can provide an alternative technique to analyze percent alcohol in alcoholic products.

Short-wave near-infrared spectrometer for alcohol determination and temperature correction

A multichannel short-wave near-infrared (SW-NIR) spectrometer module based on charge-coupled device (CCD) detection was designed. The design relied on a tungsten lamp enhanced by light emitting diodes, a fixed grating monochromator and a linear CCD array. The main advantages were high optical resolution and an optimized signal-to-noise ratio (0.24 nm and 500, resp.) in the whole wavelength range of 650 to 1100 nm. An application to alcohol determination using partial least squares calibration and the temperature correction was presented. It was found that the direct transfer method had significant systematic prediction errors due to temperature effect. Generalized least squares weighting (GLSW) method was utilized for temperature correction. After recalibration, the RMSEP found for the 25°C model was 0.53% v/v and errors of the same order of magnitude were obtained at other temperatures (15, 35 and 40°C). And an r(2) better than 0.99 was achieved for each validation set. The possibility and accuracy of using the miniature SW-NIR spectrometer and GLSW transfer calibration method for alcohol determination at different temperatures were proven. And the analysis procedure was simple and fast, allowing a strict control of alcohol content in the wine industry.