Oxidation in fish oil enriched mayonnaise: ascorbic acid and low pH increase oxidative deterioration

Area of Science:

• Food Chemistry
• Lipid Oxidation
• Emulsion Science

Background:

• Mayonnaise, an oil-in-water emulsion, is susceptible to lipid oxidation, especially when enriched with polyunsaturated fatty acids like fish oil.
• Iron and copper are known pro-oxidants that can accelerate lipid degradation in food systems.
• Ascorbic acid (Vitamin C) is often used as an antioxidant, but its behavior in complex food matrices can be multifaceted.

Purpose of the Study:

• To investigate the impact of ascorbic acid and pH on iron and copper levels and oxidation in fish oil-enriched mayonnaise.
• To elucidate the mechanisms by which ascorbic acid and pH influence lipid oxidation in this specific food model.

Main Methods:

• Mayonnaise samples enriched with 16% fish oil were prepared.
• Varying concentrations of ascorbic acid (0-4000 ppm) and pH levels (3.8-6.2) were applied.
• Oxidation markers (volatile compounds, peroxide value) and metal ion distribution (iron, copper) were analyzed in different mayonnaise fractions.

Main Results:

• Ascorbic acid facilitated iron release from the oil-water interface into the aqueous phase, particularly at low pH (3.8-4.2).
• Ascorbic acid promoted volatile oxidation products and decreased peroxide values, while low pH generally increased both.
• Low pH was proposed to break iron-protein bridges at the interface, making iron ions accessible as oxidation initiators.

Conclusions:

• Both ascorbic acid and low pH contribute to enhanced lipid oxidation in fish oil-enriched mayonnaise.
• Ascorbic acid's pro-oxidant effect at low pH is attributed to the reduction of Fe(3+) to Fe(2+), accelerating lipid hydroperoxide decomposition.