Enzymatic determination of l-malic acid in honey

Abstract

l-Malic acid determination has been carried out in honey using a direct enzymatic method. The sample solution was prepared from 2.5 g honey in 100 ml Milli-Q water. The enzymatic determination was measured spectrophoto metrically at 340 nm, using glutamate-oxaloacetate transaminase and l-malate dehydrogenase. The direct method combines precision (CV was 3.5%, at worst), good recovery (100 ± 3.5%), zero interference, simplicity, and low cost (cost was reduced by 50% using a microtest). This direct enzymatic method was applied to 20 floral honeys of Galicia (northwestern Spain) and the results ranged between 94 and 596 mg kg −1 (mean 246 mg kg −1) of l-malic acid, which is in keeping with value ranges obtained by other authors. Different clarifications [as polyvinyl-polypyrrolidone (PVPP), Carrez, Carrez with NaOH, Carrez with KOH, Carrez together with PVPP and activated charcoal] and a pair of controls have also been used but the precision and the recovery of direct enzymatic method of l-malic acid in honey did not improve.