Enzymatic synthesis of phytosteryl lipoate and its antioxidant properties

- Phytosteryl lipoate was successfully synthesized through enzymatic route.
- The maximum conversion of 71.2% was achieved under the selected conditions.
- The structure of phytosteryl lipoate was determined by FTIR, HPLC-MS and NMR.
- The oil solubility of phytosteryl lipoate was twice as high as that of phytosterol.
- The antioxidant ability of phytosteryl lipoate was better than phytosterol by peroxide value determination.

In this work, an enzymatic route for synthesizing phytosteryl lipoate was successfully set up for the first time. The structure of final product phytosteryl lipoate was determined by Fourier Transform Infrared (FTIR), Mass Spectrometry (MS) and Nuclear Magnetic Resonance (NMR). The maximum conversion of 71.2% was achieved when the following conditions were employed: 150 mmol/L phytosterol, 1: 2.5 M ratio of phytosterol to lipoic acid, 10 g/L of 4 Å molecular sieves and 60 g/L Candida rugosa in 2-methyl-2-butanol/n-hexane (1:1, v/v) at 55 °C for 96 h. The physicochemical properties including solubility and antioxidant ability of phytosteryl lipoate in oil were assessed. The results revealed that phytosteryl lipoate possessed over twice as much oil solubility as free phytosterol and also showed better antioxidant ability. Investigation on its biological functions will be the main object in the future work.