The protective role of water injection on oil quality in deep fat frying conditions

The protective role of water injection on oil quality was studied in deep fat frying conditions. Oil stability indices included acid value (AV), malondialdehyde (MDA), p-anisidine, and conjugated dienes (CDs). Water was continuously injected at flow rates of 0.1 to 1.0 and 0.1 to 0.5 mL/min/L into corn and canola oil, respectively. Frying was conducted at 170degreesC for up to 22 h. Water injection had a dual effect. In comparison with the control, water injection increased the AV of corn oil (from 0.09 to 0.59 mg/g) and canola oil (from 0.02 to 0.15 mg/g), and a contrarily protective role was found in all the other quality indices. Significant reductions in MDA concentration (from 1,600 to 497 ppb and 6,178 to 3,765 ppb), p-anisidine value (from 195 to 39 mmol/kg and 147 to 67 mmol/kg), and CDs (from 29 to 19 mM and 33 to 25 mM) were measured in corn and canola oil, respectively. MDA, p-anisidine and CD concentrations were higher when water was injected through a capillary of a wider diameter. Headspace air flow, or direct nitrogen injection were also significant factors affecting oil quality. The protective role of water stresses the need to consider this information for the extended frying applications expected in fast food outlets and restaurants.