Optimisation of extraction procedures for analysis of benzoic and sorbic acids in foodstuffs

Benzoic and sorbic acids are the most commonly used preservatives in foodstuffs. They are usually analysed by RP-HPLC. However, in view of the complexity and diversity of foodstuffs composition, appropriate sample preparation procedures are required for reliable extraction of these preservatives from the matrices. Specific extraction procedures for analysis of jams, table olives, spreadable fats, sauces, fruit juices and wines were optimised. Thus, different types of food matrices were chosen, including those with high sugar content, with high fat content and beverages (with and without alcohol). A significant set of validation data was performed through recovery and precision studies. Chromatographic separation was achieved using a C18 column (S-10 ODS2) and acetate buffer 0.005 M (pH = 4.4)-methanol (65:35) as mobile phase, 1.4 ml/min flow rate and UV detection at 235 run. The concentration of preservatives in the samples was calculated by external standard method. Benzoic and sorbic acids in jams, jellies and table olives were efficiently extracted with methanol after ground homogenization. Fortified samples, at 4 different concentration levels of benzoic and sorbic acids, presented average recoveries (after discarding outliers) for each preservative greater than 91% with a coefficient of variation (CV) less than 2.6%. Sorbic acid was extracted from spreadable fats and emulsified sauces with n-hexane and was back-extracted to an aqueous phase with acetate buffer 0.005 M (pH = 4.4). Recoveries were higher than 98% for two levels of concentration and CV lower than 2.9%. The preservatives extraction from fruit juices (orange, apple and pineapple) and wines required purification using a Sep-Pak C18 cartridge, and its elution with methanol. Average recoveries of benzoic and sorbic acids at two levels of concentration were greater than 94% with CV less than 4.0%. Eighty-seven commercial brands were analysed including table olives (29), jams (24), jellies (2) spreadable fats (25), sauces (3), fruit juices (10) and table wines (3). All samples conformed to the legal prescriptions. (C) 2003 Elsevier Science Ltd. All rights reserved.