Synthesis of piceid lipoate and the effect and micro-mechanism of alpha-lipoic acid moiety on its antioxidant activity

A lipophilic piceid lipoate (PIL) was synthesized by enzymatic method to enhance the antioxidant activity of piceid and improve its state in oil system. The highest substrate conversion of 93.71 % was obtained in γ-valerolactone using Novozym 435 as a catalyst, with a piceid/lipoic acid ratio of 1:15 (mM/mM), an enzyme dosage of 40 mg/mL, and 4 Å molecular sieves at 400 mg/mL. The lipophilicity and antioxidant activity of piceid and PIL were evaluated, which found the introduction of α-lipoic acid markedly increased the lipophilicity and antioxidant activity of piceid. The oxidation inhibition rate of PIL in bulk oil was nearly 2.0 and 1.9 times higher than piceid and butylated hydroxytoluene, indicating that PIL is a promising antioxidant for oil-based foods. The antioxidant micro-mechanisms of PIL were revealed by computational simulations, which found the lipoic acid moiety in PIL molecule enhanced its free radical scavenging capacity and improved its solubility, dispersion, and migration in bulk oil.