Biocatalytic Synthesis of Polyglycerol Polyricinoleate: A Comparison of Different Commercial Lipases

Polyglycerol polyricinoleate (PGPR, E-476) is a powerful water-in-oil emulsifier 1–5 used to manufacture stable pan release agents for the bakery industry and to stabilize low fat margarine systems with high water content. However, its main application is in the chocolate and confectionery industry,6,7 since it improves the flow properties of chocolate and vegetable fat coatings by lowering the friction between the particles suspended in the liquid fat phase. This way, the yield stress value is reduced and the liquid chocolate mass flows easily even at a low total fat content. Moreover, PGPR decreases the susceptibility of solidified chocolate to suffer fat bloom,8–10 a physical defect that appears during chocolate storage as a greyish-white film on the surface of the product. This has been a significant problem in chocolate ever since the industry began, since it leads to sensory defects. Known methods for preparing this compound involve two steps: the autocatalytic condensation of ricinoleic acid (or castor oil fatty acids) and the alkali-catalyzed reaction between the condensed ricinoleic acid and polyglycerol to give polyglycerol polyricinoleic fatty acid esters.1 However, these methods have the disadvantage of requiring very long reaction times and thus involve a large financial outlay and high energy costs. The long reaction times also adversely affect the quality of the final product, which presents problems of coloration and odour.11 Enzymatic synthesis might be regarded as an alternative for overcoming these problems since enzymes act favourably in mild temperature and pressure conditions and at neutral pH. For this reason, an enzymatic PGPR synthesis process is being developed by our research group using lipase (E.C.3.1.1.3) as catalyst. The enzymatic procedure consists of two steps. Firstly, the ricinoleic acid is polymerized by the action of Candida rugosa lipase to obtain the estolide. The optimization of this reaction step was described in previous manuscripts.12–14 Secondly, the obtained polyricinoleic acid (PR) is esterified with polyglycerol through the action of a different lipase (Fig. 1). In a previous work, twenty-four lipases were tested to catalyze this second Biocatalytic Synthesis of Polyglycerol Polyricinoleate: A Comparison of Different Commercial Lipases