Determination of synthetic phenolic antioxidants in food items using HPLC and total antioxidants using FIA approaches

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Date
2007
Authors
Yong, Yek Sing
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Abstract
Synthetic phenolic antioxidants (SPAs) are food additives that are added to food to extend their shelf life. While there is a growing trend towards using natural antioxidants, synthetic antioxidants continue to be widely used. The use of synthetic antioxidants is regulated by the Food Act and Regulations of Malaysia, which stipulates that the maximum level permitted for the combination of the synthetic antioxidants in a few food items is 200 ppm. Due to the toxicity of these SPAs, analytical techniques for their determination is required. Two analytical methods for the determination of: (i) SPAs (propyl gallate (PG), tert-butyl hydroquinone (TBHQ), butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), and (ii) total antioxidants in cooking oil, bread spread and cheese samples are described. Liquid-liquid extraction was used to isolate the SPAs from the food items. The effect of extracting solvents and extraction conditions were investigated for their recoveries using HPLC. Under the optimized HPLC conditions, baseline separation of the four SPAs in less than 8 minutes was achieved, and recoveries in the range of 93.0-108.0% for PG and TBHQ meanwhile 96.0- 101.0% and 74.0-94.0% for BHA and BHT, respectively when spiked with 50 ppm and 200 ppm SPAs to cooking oil, bread spread and cheese were found. The levels of SPAs in all food items analysed were below the legal limits. Two approaches were developed for the flow injection analysis (FIA) determination of total antioxidants based on spectrophotometric detection. In the first assay, the Fe(III)-phen system that was based on the reduction of Fe(III) to Fe(II) by the phenolic antioxidant followed by addition of 1,10- phenanthroline (phen) to form a red-orange Fe(II)-(phen)3 complex was developed. The second method (ABTS radical scavenging system) was based on the bleaching of the green coloured ABTS radical (ABTS.+) in the presence of antioxidants. The optimized FIA procedure is linear over 1.0-80.0 ppm and 1.0-50.0 ppm for Fe(III)-phen and ABTS radical system, respectively with detection limits of 0.2 and 0.5 ppm. Sampling rate of 30-40 samples h-1 was achieved. Good correlation (r2= 0.905) between the proposed methods and the manual spectrophotometric methods were found when applied to the determination of total antioxidants in 38 food items.
Description
Master
Keywords
Chemical science , Synthetic phenolic antioxidants , Food item
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