Analytica Chimica Acta 701 (2011) 139–151 Contents lists available at ScienceDirect Analytica Chimica Acta j ourna l ho me page: www.elsevier.com/locate/aca Adulteration of the anthocyanin content of red wines: Perspectives for authentication by Fourier Transform-Near InfraRed and 1 H NMR spectroscopies E. Ferrari a , G. Foca b,∗ , M. Vignali c , L. Tassi a , A. Ulrici b a Dipartimento di Chimica, Università di Modena e Reggio Emilia, Via Campi 183, 41125 Modena, Italy b Dipartimento di Scienze Agrarie e degli Alimenti, Università di Modena e Reggio Emilia, Padiglione Besta, Via Amendola 2, 42122 Reggio Emilia, Italy c Vinicola San Nazaro, Via Gonzaga 12, 46020 Pegognaga (MN), Italy a r t i c l e i n f o Article history: Received 24 March 2011 Received in revised form 23 May 2011 Accepted 26 May 2011 Available online 22 June 2011 Keywords: Wine adulteration Anthocyanins Fourier Transform-Near InfraRed 1 H NMR Multivariate classification Feature selection a b s t r a c t In the Italian oenological industry, the regular practice used to naturally increase the colour of red wines consists in blending them with a wine very rich in anthocyanins, namely Rossissimo. In the Asian market, on the other hand, anthocyanins extracted by black rice are frequently used as correctors for wine colour. This practice does not produce negative effects on health; however, in many countries, it is considered as a food adulteration. The present study is therefore aimed to discriminate wines containing anthocyanins originated from black rice and grapevine by using reliable spectroscopic techniques requiring minimum sample prepara- tion. Two series of samples have been prepared from five original wines, that were added with different amounts of Rossissimo or of black rice anthocyanins solution, until the desired Colour Index was reached. The samples have been analysed by FT-NIR and 1 H NMR spectroscopies and the resulting spectra matrices were subjected to multivariate classification. Initially, PLS-DA was used as classification method, then also variable selection/classification methods were applied, i.e. iPLS-DA and WILMA-D. The classification with variable selection of NIR spectra permitted to classify the test set samples with an efficiency of about 70%. Probably these not excellent performances are due to the matrix effect, together with the lack of sensitivity of NIR with respect to minor compounds. On the contrary, very satisfactory results were obtained on NMR spectra in the aromatic region between 6.5 and 9.5 ppm. The classification method based on wavelet-based variables selection, permitted to reach an efficiency in validation greater than 95%. Finally, 2D correlation analysis was applied to FT-NIR and 1 H NMR matrices, in order to recognise the spectral zones bringing the same chemical information. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The wine-making process for red wines production involves the extraction of different phenolic compounds. Among them, the anthocyanins are particularly relevant, because they are the mainly responsible substances for red wines’ colour. In Vitis vinifera grapes and in the corresponding wines are present malvidin, peonidin, delphinidin, petunidin and cyanidin – the aglycone moieties of anthocyanin molecules – which differ from one another for the number of hydroxyl and methoxyl groups that can serve as sub- stituents of the aromatic rings. Such aglycones occur in nature in glycosylated forms with one or more sugars [1,2]. Anthocyanins are present in Italian wines in widely varying amounts – usu- ally 100–1500 mg L -1 – depending on the grape variety, various ∗ Corresponding author. Tel.: +39 0522 522042; fax: +39 0522 522027. E-mail address: giorgia.foca@unimore.it (G. Foca). seasonal and environmental factors as well as the techniques of vinification and the length of the aging process [3]. In the Italian oenological industry, the common and standard practice used to naturally increase the colour of red wines consists in blending them with a wine very rich in anthocyanins, namely Rossissimo dell’Emilia or, simply, Rossissimo [4]. In the Asian market, on the other hand, anthocyanins extracted by black rice are fre- quently used as correctors for wine colour. This practice is boosted by the fact that the extraction of anthocyanins from black rice is very advantageous, since the total content of anthocyanins in the whole seed can reach up to 500 mg/100 g [5], and anthocyanins are mainly located in the husk, that is usually removed as refuse. Such as for the types of anthocyanins extracted by black rice, different studies have shown that the aglycone moieties mainly represented are cyanidin and peonidin [5–8]. Since the anthocyanins family con- sists of molecules structurally very similar and of proven salutary effect, it is easy to understand that the problem of using antho- cyanins extracted from black rice to increase the colour of wine is not a problem of toxicity or of food safety, but it is a merely 0003-2670/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2011.05.053