Chemical decomposition of synthetic antioxidants at high temperature
Abstract
The chemical decomposition of 2-tert-butyl-hydroxy-anisol (BHA), 2-tert-butyl-hydroxytoluene (BHT) and 2-tert-butyl-hydroquinone (TBHQ) at 175 $\pm$ 5%C in the absence of hydroperoxy or alkylperoxy radicals was studied. An attempt was made to determine the functions of those decomposed compounds in food using a model system. 2-tert-butyl-benzoquinone (TBBQ) was identified as the primary and major oxidation product of TBHQ. Interconversion between TBHQ and TBBQ was observed to play the most important role in antioxidant effectiveness and carry through effect of TBHQ. Several types of dimers by ether linkage resulting from thermolysis at frying temperature were identified. 3,3$\sp\prime$5,5$\sp\prime$-tetra-bis-(tert-butyl)-4,4$\sp\prime$-dihydroxyl-1.2-diphenylethane from BHT and 3,3$\sp\prime$-bis-(1.1-dimethyl ethyl)-5,5$\sp\prime$-dimethoxy-1,1$\sp\prime$-biphenyl-2,2$\sp\prime$-diol (DHDP) and its ethylene glycol type of isomer from BHA were determined as major decomposition products. 2,6-di-tert-butyl-4-hydroperoxy-4-methylcyclohexa-2,3-dienone (HBHT) was thermolized at frying temperature to simulate and simplify the real system containing BHT and lipid. The products included BHT, 2,6-di-tert-butyl-4-hydroxy-4-methylcyclohexa-2.5-dione (MCHD), 3,5-di-tert-butyl-4-hydroxybenzaldehyde (DBHB), 2,6-di-tert-butyl-4-hydroxymethylphenol (DBHP) and unidentified compounds having M.W. 414, 442, 274, and 278. Trace amounts of 2,6-di-tert-butylbenzoquinone (DBBQ) and quinone methide (QM) were detected. In the model system containing palmitic acid (16;0) and linoleic acid (18;2), the order of antioxidant effectiveness in protecting polyunsaturated fatty acid was TBHQ $>$ BHA $>$ BHT. In addition, significant reactivity of BHA and TBHQ but not BHT with the functional carboxyl group of fatty acid, which may lower antioxidant effectiveness, was determined using simple model systems.
Degree
Ph.D.
Advisors
Pratt, Purdue University.
Subject Area
Food science
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