Determination of olive oil 2-thiobarbituric acid reactive substances by parallel flow injection Original Research Article

A flow injection system incorporating multiple incubation coils is used for the automated determination of olive oil 2-thiobarbituric acid reactive substances (TBARS). The use of a laboratory-made parallel flow injection (PA-FI) analyser allows the simultaneous incubation of 10 samples. Olive oil samples are injected in a 2.0×10−2 M 2-thiobarbituric acid (TBA) stream in n-propanol and then acidified by merging with a 0.10 M trichloroacetic acid stream in n-propanol. The resulting reaction mixture is diverted to an incubation coil through a stream selection valve. All incubation coils, that are immersed in a water bath at 95±1°C, are loaded in 5 min and then the flow stops for 25 min. After sample incubation, the reaction mixture is cooled by passing through an ice bath and the reaction products are measured at 532 nm. The proposed PA-FI method achieves olive oil analysis without pretreatment and minimizes solvent consumption (1.9 ml of n-propanol, 2.7 mg of TBA and 16 mg of trichloroacetic acid per analysis). Precision was found to be better than 4.6% R.S.D. (n=10). The linear range was (0.4–10)×10−4 M (calculated as malondialdehyde (MDA)) and was suitable for olive oil analysis. The proposed method compares well with a manual method (relative difference 0–6.2% for the analysis of 30 olive oil samples). The analysis rate is 20 samples h−1, while individual samples are incubated for 30 min. The PA-FI analyser developed allows automation of methods that require long incubation times without loss of sampling rate, overcoming the ‘one sample at a time’ disadvantage of FI.