Antioxidant properties of chlorogenic acid and its alkyl esters in stripped corn oil in combination with phospholipids and/or water

In bulk oil, it is generally thought that hydrophilic antioxidants are more active than lipophilic antioxidants. To test this hypothesis, the antioxidant activity of phenolics with increasing hydrophobicity was evaluated in stripped corn oil using both conjugated diene and hexanal measurements. Chlorogenic acid and its butyl, dodecyl, and hexadecyl esters were used as model phenolic antioxidants with various hydrophobicities. Results showed that hydrophobicity did not correlate well with antioxidant capacity. The combination of chlorogenic acid derivatives with dioleoylphosphatidylcholine (DOPC) and/or water was also studied to determine if the physical structure in the oil affected antioxidant activity. DOPC alone made hexadecyl chlorogenate a less effective antioxidant, but it did not change the antioxidant capacity of chlorogenic acid. In contrast, the combination of DOPC and water (～400 ppm) renders chlorogenic acid a less active antioxidant, whereas it does not change the activity of hexadecyl chlorogenate. These results show, in bulk oil, that intrinsic parameters such as the hydrophobicity of lipophilized phenolics do not exert a strong influence on antioxidant capacity, but they can be highly influential if potentialized by extrinsic factors such as physical structures in the oil.