The conversion of various terpenes by oxidative biocatalysis

Abstract

Nootkatone (NK) is a sesquiterpenoid that is highly sought after in the flavour, fragrance, pharmaceutical and agricultural industries. The challenge is that it is extracted from plant species that are limited, seasonal and are not able to meet the demand. Scientists have found ways to chemically synthesize this compound, but due to the toxicity of the reagents and procedures, the resulting product does not meet the requirements to be classified as a natural product. Therefore, biocatalysis has become vital in the production of NK because it focuses on the use of renewable resources, non-toxic reagents, mild reaction conditions and cost effective methods. The production of NK by biocatalytic methods has been faced with challenges of low yield, expensive biocatalyst, low selectivity, enzyme recovery, long and tedious enzyme purification procedures. Therefore, the purpose of this research was to firstly develop an easy yet cheap method of extracting lipoxygenase (LOX) enzyme from soybeans. Secondly, the crude LOX enzyme was applied in synthesis to convert valencene to NK, before and after, purification and immobilization. Thirdly, the crude LOX enzyme was precipitated with ammonium sulfate (50%-80%) and cross-liked with glutaraldehyde to form CLEAs. The use of soybean LOX to convert VL to NK was a success with more than 90 mol% VL converted, and the highest concentration of NK was 74 mol%. This was especially significant because the reaction conditions were at pH 3-6, this has expanded the range that LOX can convert VL to NK. The emulsion challenges we encountered propelled us to developing an effective method that utilizes inorganic salts (NaCl, NaHCO3, K2CO3) to make product separation easy. There is great potential for the huge demand of natural NK to be met through this process because of it is effective, green, and sustainable. There is also an opportunity to explore the biocatalytic activity of soybean LOX in converting other terpenes or organic compounds to important oxidized compounds