Combination of visible and mid-infrared spectra for the prediction of chemical parameters of wines Ilknur Sen a , Burcu Ozturk b , Figen Tokatli a,n , Banu Ozen a a Izmir Institute of Technology, Department of Food Engineering, 35430 Urla-Izmir, Turkey b Namik Kemal University, Sarkoy Vocational School, Tekirdag, Turkey article info Article history: Received 31 May 2016 Received in revised form 16 August 2016 Accepted 18 August 2016 Keywords: Anthocyanins UV–Visible spectroscopy Fourier transform mid-infrared spectro- scopy Orthogonal partial least square regression Wine analysis Wine composition abstract Rapid and environmentally friendly methods for the prediction of chemical compositions have been an interest in the wine industry. The objective of the study was to show the potentials of combined use of visible and mid-infrared (MIR) spectroscopies to improve the prediction of various chemical compounds of wine as opposed to using mid-infrared range only. Wine samples of twelve grape varieties from two harvest years were analyzed. The chemical composition of wine samples was related to MIR and visible spectra using orthogonal partial least square (OPLS) regression technique. The prediction abilities were tested with crossvalidation and independent validation sets. The coefficient of determination of vali- dation (R 2 val ) for anthocyanin compounds of red wines were between 0.76 and 0.90, and that for total phenol content was 0.90. Range of R 2 val for glycerol, glycerol/ethanol ratio, malic acid, o-coumaric acid and °Brix were between 0.77 and 0.96. The spectral ranges that played significant roles in the predictions were also determined. The validations with independent data sets showed that the combination of visible and MIR ranges with multivariate methods improved the prediction of anthocyanin compounds and total phenols; produced comparable results for the rest of the parameters as MIR. This is the first study in the literature that shows the practical use of visible spectra along MIR. The combined use of these spectral ranges with multivariate models can be applied for the rapid, on-line determination of quality parameters and chemical profiles of wines. & 2016 Elsevier B.V. All rights reserved. 1. Introduction Polyphenol content of grapes and wines are basically grouped as flavonoids (flavonols, flavan-3-ols, anthocyanins) and non-fla- vonoids (hydroxybenzoic acids, hydroxycinnamic acids, stilbenes). Wine quality highly depends on phenolic compositions as they improve wine taste and color and also have positive health effects [1]. The color of red wine is a major concern of wine industry since it strongly affects the consumer demands. Anthocyanin content is the main reason for the color of red wine and depends on the grape variety, degree of grape ripeness, soil and climatic condi- tions, and it undergoes a progressive change from production to consumption of any wine due to polymerization, copigmentation and oxidation reactions [2,3]. In terms of white wine, flavonols are the color pigments giving the yellow color of white wines [4]. Chromatographic methods are commonly used to determine the phenolic and anthocyanin profiles of wines. However, due to their laborious and expensive work, spectroscopic methods have been offered as the rapid and reliable alternatives including near and mid-infrared spectroscopies. The wine production sector requires rapid, reliable and si- multaneous determination of analytes from the beginning of the grape ripening to the end of fermentation for monitoring and screening purposes. Online determination of wine composition enables the control of production process and ensures optimal product quality. The use of vibrational spectroscopy in wine sector started with the near infrared reflectance (NIR) spectroscopy. Re- cent studies have also focused on Fourier transform infrared spectroscopy (FTIR) technology due to advantages in the analysis of some of the wine constituents [5,6]. This technique has been employed in monitoring of grape ripening, fermentation and quantification of some chemical parameters such as organic acids, sugars or ethanol [7,8]. UV–Visible spectroscopy (UV–Vis) is an- other cost- and time-saving technique that is used in routine analysis such as determination of total phenols and color of wines. There are reports that showed the combined use of visible and NIR spectroscopies in classification of wines and in prediction of cer- tain phenolic compounds [9]. UV–Vis range along with NIR region Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta http://dx.doi.org/10.1016/j.talanta.2016.08.057 0039-9140/& 2016 Elsevier B.V. All rights reserved. n Corresponding author. E-mail addresses: ilknursen@iyte.edu.tr (I. Sen), bozturk@nku.edu.tr (B. Ozturk), figentokatli@iyte.edu.tr (F. Tokatli), banuozen@iyte.edu.tr (B. Ozen). Talanta 161 (2016) 130–137