The deuterium content of sugar in fruits is influenced mainly by two factors – the botanical and also the geographical origin of the fruit. The information of the fruit origin is kept even after fermentation of the sugar, in the molecules of ethanol. The deuterium content on the methyl group of ethanol then varies depending upon the botanical origin of the fruit. SNIF-NMR (Site-specific Natural Isotope Fractionation – Nuclear Magnetic Resonance) is a specific method for determination of the deuterium isotopic ratio (D/H) in small molecules, e.g. ethanol. This isotopic technique is widely used for determination of sugar adulteration of fruit-based beverages (wines, fruit juices..). In this thesis, the authentic samples of five different fruits (apples, oranges, grapefruits, pineapples and grapes) available in the Czech market have been collected and analyzed by SNIF-NMR. The results are presented as well as the comparison to some commercially available fruit juices and nectars.

Made available in DSpace on 2016-06-02T20:36:11Z (GMT). No. of bitstreams: 1 DissEFB.pdf: 1781956 bytes, checksum: 216e4891d9760eaec478a16a4178611c (MD5) Previous issue date: 2004-02-27 / Financiadora de Estudos e Projetos / In this work we describe the use of NMR in the biosynthetic origin study of acetic acid and acidity determination in commercial vinegar samples. The sitespecific natural isotope fractionation of hydrogen and deuterium was investigated by 2H and 1H Nuclear Magnetic Resonance Spectroscopy (SNIF-NMR). This method is based on the ratio of deuterium/hydrogen content at a specific position (methyl site) of acetic acid molecule. The acetic acid, after ethanol fermentation, can be obtained from plants sugars with different biosynthetic mechanisms C3, C4 or CAM and resulting in different isotopic ratios. In this study we measured the isotopic ratio of vinegars obtained from C3 plants 98,6 111,8 ppm, C4 plants about 130 ppm, and CAM plants 106,0 ppm. We also measured contend of agrins, which are vinegars of alcohol and wine, 115,2 129,3 ppm, and for the synthetic acetic acid with higher value, 153,5 ppm. Commercial samples were obtained in the local shopping in São Carlos SP and the standard samples were obtained from reliable origin and provided isotopic ratio values used as reference. Sample acidity was studied through 1H NMR and by titration. These techniques provided acidity between 1 and 7%. Commercial samples showed acidity about 4% that agree with the values in product labels instruction. / No presente trabalho descrevemos o uso da RMN no estudo da origem biossintética do ácido acético e na determinação da acidez em amostras de vinagres comerciais. A razão isotópica natural de hidrogênio foi estudada utilizando a espectroscopia de Ressonância Magnética Nuclear de 2H e 1H (SNIF-NMR Site Specific Natural Isotopic Fractionation studied by Nuclear Magnetic Resonance). Essa técnica está baseada na relação do conteúdo isotópico entre 2H e 1H, em partes por milhão - ppm, em uma posição específica, sítio da metila, na molécula de ácido acético. O etanol que o origina é obtido a partir dos açúcares de diferentes plantas seguindo os mecanismos biossintéticos C3, C4 ou CAM e resultando, portanto, em diferentes razões isotópicas. Nesse estudo verificamos a relação isotópica 2H/1H de vinagres obtidos de plantas C3, 98,6 - 111,8 ppm, C4, próximos a 130 ppm, e CAM, 106,0 ppm, bem como dos agrins, que são vinagres obtidos a partir de uma mistura de álcoois produzidos pela fermentação de açúcares de canade- açúcar e uva, e encontramos um valor de 115,2 129,3 ppm. A análise dos agrins mostrou que existem diferentes proporções do ácido acético oriundo da canade- açúcar e da videira. Para o ácido acético sintético foi obtido um valor superior aos anteriores, 153,5 ppm. As amostras comerciais foram coletadas no comércio de São Carlos SP e os padrões foram obtidos de fontes confiáveis e forneceram valores da relação isotópica que foram tomados como referência. A acidez das amostras foi estudada via RMN de 1H e por titulação. Os valores encontrados por essas técnicas indicaram que a acidez dos vinagres está entre 1 e 7%, sendo que as amostras comerciais apresentaram valores próximos a 4%, concordando com os valores informados nos rótulos dos produtos.

The diploma thesis deals with analytical and sensorial possibilities of control of grape wine adulteration. In the first, theoretical part of the thesis, the author introduces valid legislation regulating authorized substances in wine, as well as the wine production processes itself. The reader is acquainted with the means of wine adulteration in the Czech Republic that ensued from an analysis of unsatisfactory samples of wine, collected between 2012 -- 2015 by the SZPI (Czech Agriculture and Food Inspection Authority). The second, practical part of the thesis, describes not only grape wine and SZPI samples imitation production processes, but also methods used for their subsequent sensorial and analytical study. Besides, it interprets measured data, and compares and contrasts the possibilities and appropriateness of the sensorial evaluation and analytical study for the detection of wine adulteration.