resumo
The organic acids present in beer provide important information on the product's quality and history, determining organoleptic properties and being useful indicators of fermentation performance. NMR spectroscopy may be used for rapid quantification of organic acids in beer and different NMR-based methodologies are hereby compared for the six main acids found in beer (acetic, citric, lactic, malic, pyruvic and succinic). The use of partial least squares (PLS) regression enables faster quantification, compared to traditional integration methods, and the performance of PLS models built using different reference methods (capillary electrophoresis (CE), both with direct and indirect UV detection, and enzymatic essays) was investigated. The best multivariate models were obtained using CE/indirect detection and enzymatic essays as reference and their response was compared with NMR integration, either using an internal reference or an electrical reference signal (Electronic REference To access In vivo Concentrations, ERETIC). NMR integration results generally agree with those obtained by PLS, with some overestimation for malic and pyruvic acids, probably due to peak overlap and subsequent integral errors, and an apparent relative underestimation for citric acid. Overall, these results make the PLS-NMR method an interesting choice for organic acid quantification in beer. (C) 2010 Elsevier B.V. All rights reserved.
palavras-chave
CAPILLARY-ZONE-ELECTROPHORESIS; H-1-NMR SPECTROSCOPY; QUALITY-CONTROL; APPLE JUICES; OLIVE OILS; MULTIVARIATE-ANALYSIS; NMR; WINE; DISCRIMINATION; IDENTIFICATION
categoria
Chemistry
autores
Rodrigues, JEA; Erny, GL; Barros, AS; Esteves, VI; Brandao, T; Ferreira, AA; Cabrita, E; Gil, AM
nossos autores
Ana Maria Pissarra Coelho Gil
Professor Associado com Agregação
António de Sousa Barros
Bolseiro de pós-Doutoramentoagradecimentos
JR acknowledges the Fundacao para a Ciencia e a Tecnologia (FCT) for funding through the grant FCT SFRH/BD/31056/2006. The authors are grateful to Dr. Manfred Spraul, Bruker Biospin, Germany for useful discussions on the subject of this work and also acknowledge LabRMN at FCT-UNL for access to the facilities, which are part of the National NMR Network and were purchased within the framework of the National Programme for Scientific Re-equipment, contract REDE/1517/RMN/2005, with funds from POCI 2010 (FEDER) and FCT.