Original Paper

Analytical and Bioanalytical Chemistry

, Volume 387, Issue 6, pp 2297-2305

First online:

Fluorescent sensing layer for the determination of L-malic acid in wine

  • Félix GallartaAffiliated withLaboratory of Analytical Chemistry, Department of Chemistry, University of La Rioja
  • , Francisco Javier SáinzAffiliated withLaboratory of Analytical Chemistry, Department of Chemistry, University of La Rioja
  • , Cecilia SáenzAffiliated withLaboratory of Analytical Chemistry, Department of Chemistry, University of La Rioja Email author 

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Abstract

An enzymatic method for determining L-malic acid in wine based on an L-malate sensing layer with nicotinamide adenine dinucleotide (NAD+), L-malate dehydrogenase (L-MDH) and diaphorase (DI), immobilized by sol-gel technology, was constructed and evaluated. The sol-gel glass was prepared with tetramethoxysilane (TMOS), water and HCl. L-MDH catalyzes the reaction between L-malate and NAD+, producing NADH, whose fluorescence (λ exc = 340 nm, λ em = 430 nm) could be directly related to the amount of L-malate. NADH is converted to NAD+ by applying hexacyanoferrate(III) as oxidant in the presence of DI. Some parameters affecting sol-gel encapsulation and the pH of the enzymatic reaction were studied. The sensing layer has a dynamic range of 0.1–1.0 g/L of L-malate and a long-term storage stability of 25 days. It exhibits acceptable reproducibility [s r(%)≈10] and allows six regenerations. The content of L-malic acid was determined for different types of wine, and polyvinylpolypyrrolidone (PVPP) was used as a bleaching agent with red wine. The results obtained for the wine samples using the sensing layer are comparable to those obtained from a reference method based on UV-vis molecular absorption spectrometry, if the matrix effect is corrected for.

Keywords

Sensing layer L-Malate dehydrogenase Sol-gel L-Malate Wines