Antioxidative properties of phenolic acids and interaction with endogenous minor components during frying

Abstract

The ability of selected phenolic acids to improve the frying performance of canola oil was evaluated in a frying test. The frying performance of the oil was assessed by analysis of total polar components (TPC), level of 4-hydroxynonenal (HNE), and the rate of formation of volatile carbonyl compounds (VCC). All the tested phenolic acids; ferulic acid (FA), caffeic acid (CA), dihydrocaffeic acid (HCA), gallic acid (GA), and vanillic acid (VA) significantly increased the frying performance of canola oil triacylglycerols (CTG). At the end of the frying test, the amount of TPC in CTG was 22.9 AE 1.0% compared to a maximum of 18.8 AE 0.8% in CTG fortified with the phenolic acids. Similarly, the level of HNE was reduced by up to 45% when it was supplemented with phenolic acids. The results showed that ethyl ferulate (EF) was a better antioxidant than FA under frying conditions; HCA offered a slightly better protection than CA; and the cinnamic acid derivative, FA was better than VA, its benzoic acid analogue. A significant synergy was observed between phenolic acids and the sterol fraction isolated from canola oil. The observed synergy was attributed to the possible formation of steryl phenolates during the frying test.Practical applications: The poor thermal stability of polyunsaturated oils limits their application for prolonged frying. PUFA offer important health benefits and can improve nutritional value of fried foods. Contrary to the commonly applied synthetic antioxidants, the phenolic acids tested in this study often are part of endogenous oil components present in oilseeds and also in some oils, and are known for their positive health benefits. Thus, the simple phenolic acids, especially the cinnamic acid derivatives may be applied as potent antioxidants to protect oils during thermal processes used for food production.

Protective effect of gallic acid on the thermal oxidation of corn and soybean oils during high temperature heating

“…The result was based on a single concentration treatment (200 ppm, w/v) during very short time frying process (30, 60, and 90 min only) with only one type of vegetable oil (corn oil). The effect of gallic acid at 500 ppm on the oxidative changes (polar compounds, volatile compounds, and hydroxynonenal) of purified canola oil triacylglycerol during short period (120 min) heating at 185 o C has also been reported (21). The result was also based on the single concentration (500 ppm) of gallic acid on the thermal oxidation of purified canola triacylglycerols.…”

“…The information on the protective activity of gallic acid on the thermal oxidation of vegetable oils at frying temperature was surprisingly scarce. There was only a few reports on the protective activity of gallic acid on the thermal oxidation of vegetable oils (20,21). However, the comparative protective activity of gallic acid with the synthetic antioxidants on the thermal oxidation of vegetable oils has not been reported previously.…”

Natural antioxidants as stabilizers of frying oils*

“…Besides this antioxidant degradation phenomenon, there is also the possibility of composing new, in situ secondary antioxidants as a consequence of some physico‐chemical reactions involving antioxidants, food materials (starch and protein), and lipid degradation products during frying. For instance, it was recently observed that the reactions between endogenous phytosterols and added phenolic acids during frying can create a synergistic relationship through in situ formation of steryl ferulates, a secondary antioxidant . Indeed, the influence of components' molar ratios and other conditions necessary for such in situ synthesis requires further investigations.…”