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

Abstract

BackgroundTraditional 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.ResultsThe 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.ConclusionThe 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).

Partial least squares−near infrared spectrometric determination of ethanol in distilled alcoholic beverages

“…The direct determination of ethanol in traditional fermented alcoholic beverages using mid infrared spectroscopy with partial least squares regression (MIR-PLS) has also been reported [24]. The MIR-PLS predicted values were found to be in excellent agreement with gas chromatographic measurements.…”

“…However, it should be noted that the present procedure is probably not usable for regulatory purposes (e.g. controlling labelling) [24].…”

Assessment of trace metals and physicochemical parameters of commercially available honey in Ethiopia

“…These are mineral contents in tea (Gebretsadik and Chandravanshi, 2010), coffee (Ashu and Chandravanshi, 2011), mineral waters (Seda et al, 2013), wines (Woldemariam and Chandravanshi, 2011), ouzo (Bekele and Chandravanshi, 2012), traditional fermented alcoholic beverages (Debebe et al, 2017a). Phenolic contents (Debebe et al, 2016) and level of alcohol in fermented (Debebe et al, 2017b) and distilled (Debebe et al, 2017c) alcoholic beverages have also been reported. However, to the best of our knowledge, no systematic study on the levels of trace heavy metals and physicochemical parameters in Ethiopian honey has been made.…”

The application of spectroscopy to assess the quality of grape wines

“…Инфракрасный спектр продукта позволяет выявлять большое количество соединений, образующихся в ходе технологического процесса его получения, что позволяет осуществлять текущий контроль путем систематической обработки спектров во времени [4]. Для оценки динамики отслеживаемого процесса важно знать количественное соотношение искомых веществ, что устанавливается по интенсивности полос поглощения, отражающих присутствие соединений с данными функциональными группами в анализируемом продукте, и подготовленным градуировочным характеристикам [5].…”

“…Вино -достаточно сложный по составу продукт, различные компоненты которого имеют одинаковые функциональные группы, нахождение концентрации единственного вещества по «общей» группе возможно лишь при условии, что определяемое вещество находится в известном, постоянном количественном соотношении с веществами, имеющими эту же группу, чтобы обеспечить выделение характеристической полосы поглощения для искомого вещества и установление градуировочной характеристики по ней. Так, гидроксильную группу содержат вода, спирты, органические кислоты, фенольные вещества и др., поэтому полоса поглощения гидроксильной группы имеет недостаточную резкость и специфичность, чтобы использовать ее для количественного анализа [5]. Решение проблемы состоит в использовании для градуировки в качестве образца сравнения испытуемого продукта, что обеспечит нужное соотношение компонентов и исключит необходимость приготовления большого количества модельных растворов [9].…”