Determination of lactic, acetic, succinic, and citric acids in table olives by HPLC/UV

This paper describes a procedure performed by high performance liquid chrom atography/UV detection for quantification of the major carboxylic acids in table olives (lactic, acetic, succinic, and citric acids); derivatization o f carboxylic acids with 0-(4-nitrobenzil)-N,N'diisopropylisourea (PBNDI) wa s performed. The sample preparation involved deproteination with ethanol and the use of strong cation-exchange resin (Dowex 50W-X8) to liberate the free carboxylic acids. The same resin was used to remove the excess of derivatizing reagen t. The chromatographic separation was achieved using reverse-phase column C 18 (ODS). The mobile phase used was a gradient of water and acetonitrile at a flow-rate of 1 mL/min. The effluent was monitored using a UV detector at 265 nm. The method allowed for well-resolved peaks of lactic, acetic, succinic, and citric acids in less than 25 min. Precision and recovery assays were perfo rmed with good results for the acids under study. Nineteen samples of table olives available on the Portuguese market, includ ing nine samples of green olives and 10 samples of black olives, were succe ssfully monitored applying this methodology. The concentrations of carboxyl ic acids are expressed in percentage of moist olive pulp and ranged from no t detected to 477.3 mg of lactic acid/100 g of moist olive pulp and 9.43 to 232.1 mg of acetic acid/100 g of moist olive pulp. Citric acid was detecte d only in two samples of green table olives with concentrations of 24.7 and 188.3 mg/100g of moist olive pulp. Succinic acid was detected in five samp les of green table olives ranging from 10.1 to 25.8 mg/100 g moist olive pu lp, and in two samples of black table olives with concentrations of 10.7 an d 29.4 mg/100 g of moist olive pulp.