Biodiesels are mostly produced from lipid transesterification of vegetable oils, including those from soybean, jatropha, palm, rapeseed, sunflower, and others. Unfortunately, transesterification of oil produces various unwanted side products, including steryl glucosides (SG), which precipitate and need to be removed to avoid clogging of filters and engine failures. So far, efficient and cost-effective methods to remove SGs from biodiesel are not available. Here we describe for the first time the identification, characterization and heterologous production of an enzyme capable of hydrolyzing SGs. A synthetic codon-optimized version of the lacS gene from Sulfolobus solfataricus was efficiently expressed and purified from Escherichia coli, and used to treat soybean derived biodiesel containing 100 ppm of SGs. After optimizing different variables, we found that at pH 5.5 and 87 °C, and in the presence of 0.9 % of the emulsifier polyglycerol polyricinoleate, 81 % of the total amount of SGs present in biodiesel were hydrolyzed by the enzyme. This remarkable reduction in SGs suggests a path for the removal of these contaminants from biodiesel on industrial scale using an environmentally friendly enzymatic process.
BackgroundBiodiesels produced from transesterification of vegetable oils have a major quality problem due to the presence of precipitates, which need to be removed to avoid clogging of filters and engine failures. These precipitates have been reported to be mostly composed of steryl glucosides (SGs), but so far industrial cost-effective methods to remove these compounds are not available. Here we describe a novel method for the efficient removal of SGs from biodiesel, based on the hydrolytic activity of a thermostable β-glycosidase obtained from Thermococcus litoralis.ResultsA steryl glucosidase (SGase) enzyme from T. litoralis was produced and purified from Escherichia coli cultures expressing a synthetic gene, and used to treat soybean-derived biodiesel. Several optimization steps allowed for the selection of optimal reaction conditions to finally provide a simple and efficient process for the removal of SGs from crude biodiesel. The resulting biodiesel displayed filterability properties similar to distilled biodiesel according to the total contamination (TC), the cold soak filtration test (CSFT), filter blocking tendency (FBT), and cold soak filter blocking tendency (CSFBT) tests. The process was successfully scaled up to a 20 ton reactor, confirming its adaptability to industrial settings.ConclusionsThe results presented in this work provide a novel path for the removal of steryl glucosides from biodiesel using a cost-effective, environmentally friendly and scalable enzymatic process, contributing to the adoption of this renewable fuel.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0405-x) contains supplementary material, which is available to authorized users.
The present work covers an important gap in the field of analytic standards synthesis of the plants minor component, the acyl steryl glucosides (ASG). A simple and powerful procedure that allows the synthesis of different ASG has been introduced. The regioselective acylation of steryl glucosides on the C–6–OH of the glucose was produced using sym‐collidine and acyl chloride. The reaction was optimized analyzing the conditions to maximize the isolated yield of the monoacylated product. Practical applications: The identification and quantification of acyl steryl glucosides (ASG) and steryl glucosides (SG) is a difficult task and has become increasingly important in the food, oil and biodiesel industries. There is a lack of simple synthetic approaches to prepare ASG and commercial sources of those compounds as analytical standards are expensive and sometime do not have the required purity. In this paper we are introducing a simple, powerful and versatile procedure that allows the synthesis of different ASG in a rapid and efficient way, producing the products in high purity that will enable them to be use as standards. The present work covers an important gap in the field of analytic standards synthesis of the plants minor component, the acyl steryl glucosides (ASG). A simple and powerful procedure that allows the synthesis of different ASG has been introduced.
Steryl glucosides (SG) are common contaminants in biodiesel that form precipitates, which form and cause problems due to fouling during transport and storage. Therefore, their quantification is necessary to assess the quality of this fuel. The methods currently available for SG analysis require expensive instrumentation, need a previous concentration step by solid‐phase extraction (SPE) or are of limited use for the quantitative assessment. We developed an enzymatic method for SG quantification in biodiesel samples based on the hydrolysis of the glucoside catalyzed by a broadly specific beta glucosidase and the subsequent determination of the glucose released by the reaction. The method is non‐expensive, sensitive and was adapted to 96‐well format fluorescence plate reader, making it useful for the parallel assay of multiple samples. The enzymatic assay presented here represent a valuable tool for both quality control and the development of improved biodiesel production and purification procedures.
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