Financial support: This project was financed by a grant from IRPA Project, No.01-02-04-0000-PR, Malaysia.

Keywords: Oleyl oleate, immobilised lipase, esterification, liquid wax ester.

Wax esters are an important class of fine organics that are widely used in cosmetic industries due to the special characteristics of non-toxicity, good fat soluble properties and excellent wetting behaviour at interfaces (Willing, 1996; Mukerjee and Kiewitt, 1988). However, traditional raw materials of wax esters are often in short supply and at present too expensive for commercial exploitation. Currently, most of the wax esters used commercially are of synthetic origin. Enzymatic synthesis of wax esters can be attractive as it is very selective and can be performed at moderate temperatures and pressures as well as considered close to 'natural' and can potentially satisfy recent consumer demand. The use of lipases (triacylglycerol hydrolases, E.C. 3.1.1.3) to catalyse reactions is due to their specificity to form ester bonds, permits control of specific reactions and also increase yield (Akoh et al. 1992; Hari Krishna et al. 1999). This paper reported a high performance synthesis of oleyl oleate, by enzymatic synthesis using an immobilised lipase from Candida antartica (Novozym 435) in organic solvents.

Identification of reaction product

The presence of the oleyl oleate, oleic acid and oleyl alcohol were detected as brown spots when visualized by an iodine reagent. FTIR showed a characteristic absorption of ester bond at 1742 cm^-1. The profile of GC chromatogram showed major peak of oleyl oleate presence at retention time of 14.14 min, oleyl alcohol at 3.54 min and oleic acid at 4.29 min.

Optimisation of reaction parameters

Five parameters were chosen to optimise the synthesis of oleyl oleate, namely reaction time, temperature, various organic solvents, molar ratio of substrates and amount of enzyme. The reusability and stability of Novozym 435 on heat were also studied in term of % conversion. The optimum yield of products (>90 %) was obtained within 5 min, temperature between 40ºC to 50ºC, organic solvents with log P ³3.5, molar ratio of 2:1 and amount of enzyme of 0.2-0.4 g. Novozym 435 was also stable in the presence of heat and organic solvent and the activity was maintained at >90 % up to 9 cycles. This work suggests that oleyl oleate, a liquid wax ester can be produced at a very high yield and in a short period by esterification of oleic acid and oleyl alcohol, using immobilised lipase from Candida antartica (Novozym 435). The high percentage conversion is also essential for possible large scale synthesis.

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