Question

Why does the rate of lipid oxidation increase at very low water activities?

Answer 1

Hydration of lipid hydroperoxides, or their concentration at lipid-water interfaces, also changes the mechanism of hydroperoxide decomposition and reduces the rate of free-radical formation. ... The surface lipid was dispersed on cellulose surfaces or localized as small droplets and was very reactive.

Answer 2

Lipid Oxidation, Secondary Reactions, and Water Activity of Foods. Water acts as an antioxidant at very low levels by decreasing the catalytic activity of metal catalysts, by promoting recombination (quenching) of free radicals, and by promoting nonenzymatic browning which causes production of active antioxidants.