Physical evidence that the variations in the efficiency of homologous series of antioxidants in emulsions are a result of differences in their distribution.
BACKGROUND
The relationships between the hydrophilic-lipophilic balance (HLB) of antioxidants (AOs) and their distributions and efficiencies in emulsions are not fully understood. Recent reports indicate that, for series of homologous antioxidants of different hydrophobicity, the variation of their efficiency with the HLB of the AO increases with the alkyl chain length up to a maximum (C3-C8ester) followed by a decrease (cut-off effect).


RESULTS
We determined the distributions of a series of caffeic acid derivatives in intact soybean emulsions by employing a specifically designed chemical probe located in the interfacial region of the emulsion. We also determined the AO efficiencies in the very same emulsions. We demonstrate that the variation of the percentage of AO in the interfacial region of soybean oil-in-water emulsions with the AO HLB parallels that of their antioxidant efficiency.


CONCLUSIONS
The results provide physical evidence that the variations in the efficiency of homologous series of antioxidants in emulsions are the result of differences in their distribution. The results confirm that, with other things being equal, there is a direct relationship between the percentage of AO in the interfacial region of the emulsions and their efficiency, providing a natural explanation, based on molecular properties, of the cut-off effect. © 2016 Society of Chemical Industry.
REQUIMTE-LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007, Portugal.
Marlene
M
Costa
REQUIMTE-LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007, Portugal.|Department of Physical Chemistry, Faculty of Chemistry, University of Vigo, Vigo, 36200, Spain.
Sonia
S
Losada-Barreiro
REQUIMTE-LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007, Portugal.
Fátima
F
Paiva-Martins
Department of Physical Chemistry, Faculty of Chemistry, University of Vigo, Vigo, 36200, Spain.
Carlos
C
Bravo-Díaz
D000975:Antioxidants / Q000032:analysis / Q000737:chemistry*; D002109:Caffeic Acids / Q000032:analysis / Q000737:chemistry*; D003979:Diazonium Compounds / Q000032:analysis / Q000737:chemistry; D004655:Emulsions; D005217:Fat Emulsions, Intravenous / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D007202:Indicators and Reagents / Q000032:analysis / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D008970:Molecular Weight; D013024:Soybean Oil / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry
D000975:Antioxidants; D002109:Caffeic Acids; D003979:Diazonium Compounds; D004655:Emulsions; D005217:Fat Emulsions, Intravenous; D007202:Indicators and Reagents; D013501:Surface-Active Agents; C474929:octyl caffeate; C000588778:propyl caffeate; C042405:methyl caffeate; D013024:Soybean Oil; C040048:caffeic acid
antioxidant distribution; antioxidant efficiency; caffeic acid; cut-off effect; pseudophase model; soybean