Antioxidant activity of bicarbonates and carbonates in vegetable oils at frying temperatures

Abstract: This study found that bicarbonates and carbonates including NaHCO₃, Na₂CO₃, KHCO₃, and K₂CO₃ had significant antioxidant activity in soybean oil (SBO) heated at 180 °C. KHCO₃ and K₂CO₃ had stronger activity than NaHCO₃ and Na₂CO₃. KHCO₃ at 5.5 mEq/L (0.060 wt.%) and K₂CO₃ at 5.5 mEq/L (0.041 wt.%) were more effective than 0.02 wt.% tert-butylhydroquinone (TBHQ) in preventing oxidation of SBO. The study on the concentration effect of KHCO₃ and K₂CO₃ revealed that the activity increased with increasing their concentrations up to 5.5 mEq/L and decreased beyond it. These inorganic bases were also effective in preventing other vegetable oils including avocado, canola, corn, high oleic soybean, and olive oils from oxidation during heating at 180 °C. Correlation tests showed that the activity weakly or moderately correlated with g- and d-tocopherols. When the mixture of KHCO₃ and each tocopherol was examined in stripped SBO, synergism between KHCO₃ and a-tocopherol was observed while no synergism was found with g- and d-tocopherols. Interactions of KHCO₃ with other antioxidants including rosemary extract, epigallocatechin gallate, ascorbic acid, and ascorbyl palmitate were examined, and it was found that it had additive or synergistic effect with these antioxidants showing its potential as co-antioxidant with other antioxidants. A micro-frying study confirmed the antioxidant activity of KHCO₃ during frying of potato cubes in SBO and canola oil. A study on the effect of KHCO₃ in the presence of free fatty acid indicated that reducing the prooxidant activity of free fatty acid could be one of the mechanisms of its antioxidant activity in addition to the synergism with tocopherols. Other possible mechanisms and factors affecting the antioxidant activity of bicarbonates and carbonates will also be discussed.