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The contents of vitamin C (ascorbic and dehydroascorbic acids) and other organic acids such as citric, oxalic, fumaric, malic and glutamic, were determined by HPLC in 54 samples of tomato, white onion, cucumber, pepper, garlic, and 'gazpacho' elaborated using the previous vegetables. Tomato and garlic had the highest amounts of organic acids, while cucumber presented the lowest content. Citric and glutamic acids presented the highest mean concentrations. The bulb vegetables presented higher concentrations of glutamic and citric acids than the fruit vegetables. Pepper was the vegetable with the highest content of vitamin C, followed by tomato and 'gazpacho'. Mean value of ascorbic acid/dehydroascorbic acid ratio varied between 0.29 and 2.53 for cucumber and tomato, respectively. 'Gazpacho' samples had a lower ascorbic acid/dehydroascorbic acid ratio than the vegetables used in its elaboration, which suggests that some amount of ascorbic acid may be enzymatically oxidized to dehydroascorbic during the elaboration. Se determinaron los contenidos de vitamina C (acidos ascorbico y deshidroascorbico) y otros acidos organicos como citrico, oxalico, fumarico, malico y glutamico, por HPLC, en 54 muestras de tomate, cebolla blanca, pepino, pimiento, ajo y 'gazpacho' elaborado a partir de estos vegetales. Tomate y ajo fueron los que presentaron mayores contenidos de acidos organicos, mientras que en pepino se encontro el menor contenido. Los acidos organicos mayoritarios fueron citrico y glutamico. Los bulbos presentaron las mayores concentraciones de acidos glutamico y acido citrico de los frutos. El pimiento fue el vegetal que presento los mayores contenidos de vitamina C, seguido de tomate y 'Gazpacho'. La relacion entre acido ascorbico/acido dehidroascorbico oscilo entre 0,29 y 2,53 para pepino y tomate, respectivamente. Las muestras de 'gazpacho' mostraron una relacion acido ascorbico/acido dehidroascorbico inferior al de los vegetales usados en su elaboracion, lo que sugiere que una cierta cantidad de acido ascorbico se oxida enzimaticamente a dehidroascorbico durante su elaboracion. [ABSTRACT FROM AUTHOR]

Abstract: The evaluation of nutritional or functional components in grain products is an important feature for the industry, especially when recent regulations require a correct nutrition labelling, valid during all the shelf life of the product. For that reason, industry usually makes many efforts to develop simple and reliable analytical methods that can be easily applied in any quality control laboratories for routine analysis. Spectrofluorimetric analysis of thiamine and riboflavin are sensitive, but need specific equipment. A few HPLC-UV methods have been described but they are less sensitive, and present difficulties due to interfering compounds, particularly in complex food matrixes, as grains and derivatives. A combination of extraction and separation systems, that allows enough sensitivity, precision and accuracy for the analysis of vitamin B1 and B2 in complex cereal food products, by isocratic UV-HPLC, in a single wavelength simultaneous separation is presented, with the advantage of using low-cost equipment requirements, simple sample pre-treatment and short time. The achievement of this goal has involved the optimization of compatible extraction and measurement protocols for cereal matrices, comparing seven different separation conditions and six extraction/clarification matrices analysis. The selected method was comparatively validated and compared to reference AOAC spectrofluorimetric methods, providing comparable linearity and accuracy, with better specificity and precision parameters, as well as practical applicability. [Copyright &y& Elsevier]