Influence of pH, EDTA, α-tocopherol, and WPI oxidation on the degradation of β-carotene in WPI-stabilized oil-in-water emulsions

- β-Carotene emulsion was more chemically stable at higher pH (6.0, 7.0) than lower pH (3.0, 4.0).
- β-Carotene degradation in oil-in-water emulsions could be retarded with addition of both EDTA and α-tocopherol.
- α-Tocopherol was much more effective than EDTA on improving β-carotene stability in emulsion.
- There is a good correlation between the protein oxidation and β-carotene loss.

The aim of the present study was to examine the factors (pH, iron chelators, free radical scavengers) influencing the chemical stability of WPI-stabilized β-carotene emulsions and investigate the correlations between WPI oxidation and β-carotene degradation during the storage of emulsions. The pH of the emulsion had a significant influence on the stability of β-carotene, with rapid degradation in emulsions at low pH (3.0, 4.0) and relatively higher stability at high pH (6.0, 7.0). Addition of EDTA or α-tocopherol significantly increased the stability of β-carotene, exhibited a greater improvement at pH 7.0 compared to pH 4.0 and α-tocopherol was much more effective than EDTA. It revealed that both transition metals and free radicals induced β-carotene degradation, nevertheless free radicals were found to be the predominant mechanism of β-carotene degradation. WPI oxidation was measured by the loss of tryptophan fluorescence and increase in fluorescent protein oxidation products using fluorescence spectroscopy. The tryptophan fluorescence decreased in all samples during the storage and emulsions with more protein oxidation products exhibited greater β-carotene degradation rate, which confirmed that there existed a good correlation between the protein oxidation and β-carotene loss.