The use of derivatives and chemometrics to interrogate the UV–Visible spectra of gin samples to monitor changes related to storage

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Highlights

  • Changes related with gin storage conditions were evaluated using UV-VIS spectroscopy.

  • Derivatives allowed for a better interpretation of the relevant features in the UV-VIS spectra.

  • Specific wavelengths in the UV-VIS were associated with gin oxidation.

Abstract

Extensive research has been carried out to study and characterise different properties of alcoholic beverages using spectroscopy methods. Although UV-VIS spectroscopy is being used for the routine analysis of several beverages and foods, it has not been extensively used as a high throughput method. The objective of this study was to evaluate the application of derivatives to interrogate the UV-VIS spectra of gin samples to monitor changes related with storage conditions. Samples were analysed using an UV-VIS (200–800 nm) spectrophotometer with 1 cm path length. The raw spectra, second, third and fourth derivatives were used to analyse and interpret the UV-VIS spectra related to storage conditions. The results of this study indicated that the use of derivatives (third and fourth) as pre-process method to the UV-VIS spectra of gin samples allowed for a better identification of wavelengths as well as interpretation of the spectra associated with the different storage conditions.

Introduction

Gin is a flavoured alcoholic beverage that generally contains between 40 and 50% alcohol [[1], [2], [3], [4], [5]]. Originated from Holland, gin was initially used by doctors as a formulation for disorders relating to the stomach [[1], [2], [3], [4], [5]]. It was believed that the properties of the juniper berries which were infused in the gin were responsible for this medicinal and health benefits [[1], [2], [3], [4], [5]]. The fashion for gin in the eighteenth century led to a dramatic increase in the production and consumption of gin (approximately 53 L/person/year are consumed in England) and this beverage is among the most widely consumed spirits around the globe after scotch whisky and vodka [6].

The taste of gin is characterized by the botanicals added to it where essential oils and aroma are infused into the gin during this distillation procedure with other ingredients such as Juniper berries (Juniperus communis), angelica roots (Archangelica officinalis), coriander seeds (Coriandrum sativum), orange and lemon peels give gin its characteristic flavour [[1], [2], [3], [4], [5], [6]]. In addition, the use of this flavouring ingredients contributes with other compounds such as phenolic and flavonoids [[1], [2], [3], [4], [5], [6]].

In the past, extensive research has been carried out to study and characterise different properties of alcoholic beverages using methods based in vibrational spectroscopy [[7], [8], [9], [10]]. The routine use of UV-VIS spectroscopy provides with an easy, rapid and economical method allowing for the analysis of different compounds in beverages as reported by other authors [[11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]]. However, most of these methods are only based in the identification of single wavelengths related with specific chromophores in the sample, even if the whole scan is collected during the analysis [10]. Therefore, this rich data UV-VIS spectrum is not fully utilised and important information about the chemical composition of the sample is not analysed or even lost. Nowadays, the incorporation of multivariate data analysis and processing methods (e.g. derivatives, smoothing) provide with new means to mine and better interrogate spectroscopic data in the beverage and food industries [9,11,22,23].

The objective of this study was to evaluate the application of derivatives to interrogate the UV-VIS spectra of gin samples and to monitor changes related with storage conditions.

Section snippets

Gin samples

Samples (n = 12) were sourced from a commercial distillery in the Mornington Peninsula (Victoria, Australia). Commercial bottles (approx. 500 mL) were stored at room temperature (approx. 25–28 °C) and in the presence of oxygen, while another set of samples were kept devoid of oxygen and stored at lower temperature (4 °C). In addition, one set of samples were bottled in the presence of atmospheric oxygen while the other samples were bottled under vacuum. Therefore, the sample set was comprised

Spectra interpretation

Fig. 1, Fig. 2, Fig. 3 shows the raw UV-VIS spectra of gin samples sourced from different storage conditions and after pre-processing using the second, third and fourth derivative, respectively. The raw UV-VIS spectra of the gin samples showed only a single absorbance at 27 nm (Fig. 1) while the second and third derivatives showed slight changes in wavelengths around 368 nm, 320 nm, 300 nm, 275 nm and 230 nm (Fig. 2 panel A and B). In addition, the third derivative shows troughs around 286 nm

Conclusions

The raw UV-VIS spectra of the gin samples did not show the level of information needed to differentiate between the storage conditions. The pre-processing of the spectra (e.g. second, third and fourth derivatives) allowed for a better identification of wavelengths associated with the storage conditions and enhance the information derived from the analysis. In addition, the use of derivatives improves the ability of chemometric methods (e.g. PCA) coupled with UV-VIS spectra to analyse gin

Acknowledgments

The authors acknowledged Bass and Flinders Distillery for providing samples and giving an insight into their distillery which have been crucial to this work. Mathew Quinn from Agilent Australia to provide access to the UV-VIS spectrophotometer. The support of RMIT University is acknowledged.

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