Enzymatically catalyzed hydrolysis of diglycerides in shea oils

Current priorities of oil refiners consist in strict compliance with environmental regulations, reduction of operating costs and increased quality of finished products ; the use of enzymes in the refining process helps meeting these challenges with gentler operating conditions and limited environmental impact. Rectifying fat quality is another aspect ; some high acidity crude oils contain high levels of diglycerides, which is the case for palm oil, rice bran oil or shea butter. Diglycerides are not easily removed by refining ; their presence in the crude oil has a negative effect on the formation of highly toxic glycidyl esters. Although some refining methods are efficient to minimize them, it may be interesting to enzymatically treat the crude oil upstream. Diglycerides have a considerable impact on kinetics of fat crystallization and also, in the case of palm oil, on the olein cloud points. This research specifically concerns enzymatic rectification of shea butter by using NS400282 enzyme developed by Novozymes, and its effect on crystallization. This enzyme allows degradation of diglycerides into free fatty acids and glycerol. Shea butter has the particularity of being used in food and in cosmetics. For cosmetics, both crude or refined shea butters are intended ; for food application, it is often solvent fractionated, the stearin being an ingredient for CBE and the olein having cosmetic applications. In this work, four commercial matrices were studied: crude shea butter, refined shea butter, shea butter stearin and shea butter olein. In order to optimize the enzymatic treatment, different routes (single and multi-step) and different enzyme dosages were investigated, supported by GC for the diglyceride content and by HPLC for the triglyceride composition. Crystallization properties of the untreated and enzymatically treated (after neutralization) shea matrices were then compared, using p-NMR melting profiles, DSC data and powder XRD polymorphic patterns.