Kilogram-scale ester synthesis of acyl donor and use in lipase-catalyzed interesterifications

Abstract

Scaling up of Lipozyme-catalyzed ester synthesis with >99% conversion and a reflux trap to remove product water from the reaction mixture is reported. Ethyl stearate was synthesized in 2000-g batch reactions from technical stearic acid. The ethyl stearate was purified to 97% by crystallization and interesterified with sunflower seed oil by means of a lipase catalyst to investigate reaction parameters of temperature, substrate ratio, enzyme content and catalyst water activity. The endpoint of the reaction was defined as the incorporation of stearate into sunflower seed oil corresponding to the amount of stearate necessary to be incorporated into palm oil mid-fraction to produce a cocoa butter substitute. No tristearate was formed at the reaction endpoint in any of the reactions conducted. Reaction times decreased and levels of free fatty acids and diglycerides increased with increasing temperature and with increasing ratio of acyl donor to triglyceride. Increasing the enzyme content of the reaction mixture reduced reaction times but caused higher levels of free fatty acids and diglycerides. In reactions catalyzed by Lipozyme of defined water activity, the shortest reaction times were obtained at intermediate water activity, while free fatty acid and diglyceride levels increased with water activity. When the interesterification reaction was carried out in refluxing pentane with the condensed solvent dried by passage through a reflux trap, the free fatty acid and diglyceride levels were reduced to 6 and 3.3%, respectively.