Analytical Sciences

A Spectrophotometric Procedure for Malic Acid Determination in Wines Employing a Multicommutation Approach

Joyce F. S. de SANTANA, Mônica F. BELIAN, and André F. LAVORANTE

Departamento de Ciências Moleculares, Universidade Federal Rural de Pernambuco, Rua Dom Manuel de Medeiros, S/N, Dois Irmão, 52171-900 Recife, PE, Brasil

This work describes an automated procedure to determine L-malic acid (MA) in wine samples using a multicommuted flow analysis. The MA quantification was based on an enzymatic reaction between MA and L-malate dehydrogenase (L-MDH) in the presence of nicotinamide adenine dinucleotide (NAD⁺), producing nicotinamide adenine dinucleotide dehydrogenase (NADH), which was monitored at 340 nm. The L-MDH was immobilized on a surface of modified silica with amino groups in the presence of glutaraldehyde. For studying optimization, the system was maintained with 200 μL (288 U) of the L-MDH in 0.5 g of modified silica. Under the optimum experimental conditions, a linear response ranging from 0.1 to 1.5 g L⁻¹ MA (R = 0.997 and n = 7), a detection (3σ criterion) and quantification (10σ criterion) limit estimated at 0.02 and 0.06 g L⁻¹, respectively, a standard deviation relative of 1.8% (n = 7) for a sample of 0.5 g L⁻¹ MA, a sampling rate of 67 samples per hour were achieved. Analyzing ten wines samples and applying the t-test to the results found and those obtained using reference procedures (HPLC) provided no significant differences at the 95% confidence level.

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