title: A digital image-based method for determining of total acidity in red wines using acid-base titration without indicator.
abstract: This work proposes the use of digital image-based method for determination of total acidity in red wines by means of acid-base titration without using an external indicator or any pre-treatment of the sample. Digital images present the colour of the emergent radiation which is complementary to the radiation absorbed by anthocyanines present in wines. Anthocyanines change colour depending on the pH of the medium, and from the variation of colour in the images obtained during titration, the end point can be localized with accuracy and precision. RGB-based values were employed to build titration curves, and end points were localized by second derivative curves. The official method recommends potentiometric titration with a NaOH standard solution, and sample dilution until the pH reaches 8.2-8.4. In order to illustrate the feasibility of the proposed method, titrations of ten red wines were carried out. Results were compared with the reference method, and no statistically significant difference was observed between the results by applying the paired t-test at the 95% confidence level. The proposed method yielded more precise results than the official method. This is due to the trivariate nature of the measurements (RGB), associated with digital images.
authors.affiliation: Universidade Federal da Paraíba, CCEN, Departamento de Química, P.O. Box 5093, Zip Code 58051-970 João Pessoa, PB, Brazil.
authors.forename: Adamastor Rodrigues
authors.initials: AR
authors.lastname: Tôrres
authors.forename: Wellington da Silva
authors.initials: Wda S
authors.lastname: Lyra
authors.forename: Stéfani Iury Evangelista
authors.initials: SI
authors.lastname: de Andrade
authors.forename: Renato Allan Navarro
authors.initials: RA
authors.lastname: Andrade
authors.forename: Edvan Cirino
authors.initials: EC
authors.lastname: da Silva
authors.forename: Mário César Ugulino
authors.initials: MC
authors.lastname: Araújo
authors.forename: Edvaldo da Nóbrega
authors.initials: Eda N
authors.lastname: Gaião
mesh_terms: D000143:Acids / Q000032:analysis* / Q000737:chemistry; D000468:Alkalies / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D012015:Reference Standards; D012972:Sodium Hydroxide / Q000737:chemistry; D014920:Wine / Q000032:analysis*
chemical_list: D000143:Acids; D000468:Alkalies; D012972:Sodium Hydroxide