Toxicity fatty-ester synthesis

SCHEME 1 Ryoto sugar ester synthesis is based on transesteriiication of sucrose with a methyl fatty acid ester under conditions in which methanol is continuously removed. The product includes a complex mixture of K-soaps, diesters and mono-/ diglycerides, as well as the sucrose monoester when produced from crude beef tallow. An excess of sucrose is required (3 mol) to enhance the yield of the monoester over higher substituted products. DMF must be recovered for economic operation and because of its toxicity. 

The liver synthesizes two enzymes involved in intra-plasmic lipid metabolism hepatic triglyceride lipase (HTL) and lecithin-cholesterol-acyltransferase (LCAT). The liver is further involved in the modification of circulatory lipoproteins as the site of synthesis for cholesterol-ester transfer protein (CETP). Free fatty acids are in general potentially toxic to the liver cell. Therefore they are immobilized by being bound to the intrinsic hepatic fatty acid-binding protein (hFABP) in the cytosol. The activity of this protein is stimulated by oestrogens and inhibited by testosterone. Peripheral lipoprotein lipase (LPL), which is required for the regulation of lipid metabolism, is synthesized in the endothelial cells (mainly in the fatty tissue and musculature). 

The use of methanol offers the best results in the trans-esterification of oils and fats. Compared with other alcohols, methanol requires shorter reaction times and smaller catalyst amounts and alcohol/oil molar ratios [10,12,15,16,51,52]. These advantages lead to reduced consumption of steam, heat, water, and electricity, and use of smaller processing equipment to produce the same amount of biodiesel. Biodiesel applications continue to expand. Thus, in addition to its use as fuel, biodiesel has been employed in the synthesis of resins, polymers, emulsifiers, and lubricants [53-64]. Concerning the range of applications, new biodiesel production processes should be considered as alternatives to the production based on methanol. Currently, methanol is primarily produced from fossil matter. Due to its high toxicity, methanol may cause cancer and blindness in humans, if they are overexposed to it. Methanol traces are not desired in food and other products for human consumption [15]. In contrast, ethanol emerges as an excellent alternative to methanol as it is mainly produced from biomass, is easily metabolized by humans, and generates stable fatty acid esters. Additionally, fatty acid ester production with ethanol requires shorter reaction times and smaller amounts of alcohol and catalyst compared to the other alcohols, except methanol, used in transesterification processes [11,15,16]. 

The LDL receptor pathway assures a constant steady-state level of cellular cholesterol. This is accomplished both by adjusting cellular cholesterol synthesis according to ambient LDL levels and by altering LDL receptor number to limit the amount of LDL getting into cells. Like free fatty acids, unesterified cholesterol can be toxic to cells. The formation of cholesterol esters protects cells from cholesterol toxicity. 

Biocatalysis has been used for synthesis of surfactants with different hydrophilic groups that are linked to the hydrophobic fatty chain via ester, amide or glycosidic bonds. Among the most crucial parameters to be considered for enzymatic synthesis are the different solubility characteristics of the hydrophobic and hydrophilic reactants. The use of hydrophilic solvents for increasing the solubility of hydrophilic components increases the toxicity of the medium and affects enzyme activity. An alternative would be to modify the hydrophilic moiety in order to increase its solubility in the hydrophobic component. Solubility may also be improved by increasing the temperature, for which the use of thermostable enzymes would be beneficial. Various groups of surfactanfs for which enzymafic synthesis has been applied are described below. 

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