Enzymatic determination of citric acid in honey by using polyvinylpolypyrrolidone clarification

To characterize honey types, a citric acid determination may be useful. A citric acid determination on honey was carried out with previous polyvinylpolypyrrolidone (PVPP) clarification followed by the Boehringer-Mannheim GmbH enzymatic test. The sample solution was prepared from 2 g of honey in 100 mL of Milli-Q water. A volume of 10 mL of this sample was clarified with PVPP stirring for 1 min and filtered. The enzymatic determination was measured spectrophotometrically at 340 nm, using citrate lyase, L-malate dehydrogenase, and L-lactate dehydrogenase. With these conditions, there were no observed interference effects. The proposed method improves precision [coefficient of variation (CV) between 0.26% and 1.60%] and recovery (between 98.0% and 100.9%) on the direct enzymatic analysis (% CV between 1.02 and 2.66 and recovery between 84.0% and 115.6%). Furthermore, the cost was reduced 70% using a microtest. The method was applied to 20 honeys of Galicia (northwestern Spain), and the results ranged between 44.2 and 827.0 mg of citric acid/kg of honey (mean = 192.9 mg/kg).