Free fatty acids acid-catalyzed esterification

Apart from a few reports" on solid acid catalyzed esterification of model compounds, to our knowledge utilization of solid catalysts for biodiesel production from low quality real feedstocks have been explored only recently. 12-Tungstophosphoric acid (TPA) impregnated on hydrous zirconia was evaluated as a solid acid catalyst for biodiesel production from canola oil containing up to 20 wt % free fatty acids and was found to give ester yield of 90% at 200°C. Propylsulfonic acid-functionalized mesoporous silica catalyst for esterification of FFA in flotation beef tallow showed a superior initial catalytic activity (90% yield) relative to a... 

We now report on the esterification of free fatty acids and phthalic anhydride to obtain the corresponding esters in quantitative yield and high purity (aeid number <0.1 mg KOH/g) as well as on acid catalyzed fat splitting at temperatures from 140-200°C. 

The lower cost materials tend to be high in free fatty acids and thus require pretreatment before they can be transesterified with alkaline catalysts. The pretreatment typically involves sulfuric acid-catalyzed esterification of the free fatty acids to methyl esters (Canakci Van Gerpen, 2001). 

The various process modes are applied primarily on the basis of the properties of the feed mixture. Solids are processed mainly in single stage or multiple stage operational mode. Fluid feed mixtures containing compounds of similar solubility in the solvent are best treated in a multiple stage countercurrent process. The separation of isomers falls within the field of chromatography or selectively catalyzed reactions. Chemical reactions, e.g. esterification of free fatty acids, may be part of the separation process. 

Neutralization of Oils by Pre-Esterification. The free fatty acids present in the raw material are esterified with methanol. The proton-catalyzed esterification can be carried out homogeneously [204]. However, the result is that some of the acidic catalyst is... 

Wax ester biosynthesis probably involves an acyl transfer mechanism. The high thioesterase activity found in crude plant extracts makes it difficult to demonstrate acyl-CoA involvement in wax ester synthesis. However, partial purification of an acetone powder extract from the leaves of B. oleracea gave a protein fraction that catalyzed an acyl-CoA-dependent esterification of fatty alcohols (222). Additionally the acetone powder extract from B. oleracea leaves appeared to catalyze the direct transfer of acyl moieties from phospholipids to fatty alcohols. The leaf extract also catalyzed under appropriate conditions the esterification of fatty alcohols to free fatty acids. The transacylase mechanism is likely to be the main mechanism of wax ester synthesis in vivo. The fact that labeled wax esters were synthesized by a membrane-bound microsomal fraction from Hordeum vulgare leaves following incubation with radioactive alcohols, but not after incubation with free fatty acids (17), is consistent with the proposed acyl transfer mechanism. In E. gracilis the acyl-CoA reductase is functionally coupled to the acyl transferase (227). Both of these activities were solubilized from the microsomes... 

Based on the substrates involved in the lipase-catalyzed reactions, they can be classified into different categories esterification, hydrolysis, acidolysis, alcoholysis and interesterification (1). Direct esterification reaction may be enqjloyed for the preparation of stmctured lipids by reacting free fatty acids with glycerol. However, this process is not commonly used in stmctured lipid production. The major problem is that the water molecules are formed as a result of the esterification reaction. The water molecules so produced need to be removed in order to prevent the hydrolysis of the product. Hydrolysis is the... 

Properties such as large interfacial area and an ability to solubilize both oil-soluble and water-soluble reactants in a single phase system makes microemulsions ideal as reaction media (Flanagan and Singh, 2006 Gaonkar and Bagwe, 2002). For example, Morgado and co-workers (1996) nsed a continnons reversed micellar system to synthesize lysophospholipids and free fatty acids from lecithin hydrolysis, with applications to the food, pharmaceutical and chemical industries. Hydrolysis was catalyzed by porcine pancreatic phospholipase A. Carvalho and Cabral (2000) reviewed the use of reversed micellar systems as reactors to carry out lipase-catalyzed esterification, biocatalysis, transesterificadon, and hydrolysis reactions. 

Normally, g. are made by acid-catalyzed - esterification of free fatty acid and glycerol or by - transesterification of glycerol and - fatty acid methyl esters. 

Lipase is known to catalyze esterification through an acyl-intermediate formed between the fatty acid substrate and the enzyme. Free enzyme can bind fatty acid to produce either this intermediate or the ester product. With a high concentration of alcohol, the acyl-intermediate will be consumed, and the enzyme may then start to bind product and catalyze its hydrolysis, thereby reversing the reaction. When present in an excess of fatty acid, however, most of the enzyme is found in the acylated form, preventing it from binding the product (15,16). 

LDL binds specifically to lipoprotein receptors on the cell surface. The resulting complexes become clustered in regions of the plasma membrane called coated pits. Endocytosis follows (see Fig. 13-3). The clathrin coat dissociates from the endocytic vesicles, which may recycle the receptors to the plasma membrane or fuse with lysosomes. The lysosomal proteases and lipases then catalyze the hydrolysis of the LDL-receptor complexes the protein is degraded completely to amino acids, and cholesteryl esters are hydrolyzed to free cholesterol and fatty acid. New LDL receptors are synthesized on the endoplasmic reticulum (ER) membrane and are subsequently reintroduced into the plasma membrane. The cholesterol is incorporated in small amounts into the endoplasmic reticulum membrane or may be stored after esterification as cholesteryl ester in the cytosol this occurs if the supply of cholesterol exceeds its utilization in membranes. Normally, only very small amounts of cholesteryl ester reside inside cells, and the majority of the free cholesterol is in the plasma membrane. 

In the DOD, phytosterols are present in both the free and esterified forms with fatty acids. Therefore, the first step in the extraction of phytosterols is conversion of phytosterol fatty esters into free phytosterols. This is achieved either by hydrolysis or trani-esterification. Hydrolysis could be carried out under strong basic conditions (saponification with further acidulation), under strong acidic conditions, or under chemical or enzyme (specific or nonspecific) catalyzation. Re-esterification of phytosterols occurs during methyl ester distillation as a result of the high temperatures involved therefore, a further trani-esterification step for free sterols is required. Esterification of phytosterols or trani-esterification of sterol fatty acid esters is the second step in this process. Methanol is the most commonly used alcohol, and it leads to methyl esters, which are characterized by a higher volatility, however, other Ci to C4 alcohols may also be used. Esterification and trans-esterification of fatty acids or phytosterols can be catalyzed by metal alcoholates, or hydroxide, by organic catalysts, or by enzymes (Table 7). 

Excess cholesterol can also be metabolized to CE. ACAT is the ER enzyme that catalyzes the esterification of cellular sterols with fatty acids. In vivo, ACAT plays an important physiological role in intestinal absorption of dietary cholesterol, in intestinal and hepatic lipoprotein assembly, in transformation of macrophages into CE laden foam cells, and in control of the cellular free cholesterol pool that serves as substrate for bile acid and steroid hormone formation. ACAT is an allosteric enzyme, thought to be regulated by an ER cholesterol pool that is in equilibrium with the pool that regulates cholesterol biosynthesis. ACAT is activated more effectively by oxysterols than by cholesterol itself, likely due to differences in their solubility. As the fatty acyl donor, ACAT prefers endogenously synthesized, monounsaturated fatty acyl-CoA. 

Non-specific esterification of wood sterols can be performed chemically (www. freshpatents.com/Phytosterol-esterification-product-and-method-of-make-same-dt-20070628ptan20070148311.php) however, enzymatic esterification with lipases has the potential advantages of higher specificity and mild reaction conditions which are desirable, both from process and environmental perspectives. More than 20 lipases were previously screened for their ability to catalyze the transesterification of wood sterols and fatty acid esters (Martinez et al. 2004). The goal was now to screen among them those specific for stanol esterification, so as to obtain a product consisting in mostly esterified stanols and mostly free sterols (see Fig. 6.3.4) amenable for separation through short-path distillation. 

Surprisingly, esterification of fatty acids with simple sugars, such as glucose and mannitol, in AOT-based microemulsions did not take place at all [82]. No reaction was seen with either of two different lipases. This is probably due to poor phase contact between the very hydrophilic sugar molecule in the water pool and the fatty acid that resides in the hydrocarbon domain. Sugar monoesters can be produced in high yields by lipase-catalyzed esterification in a water-free medium [90]. 

Lipase-catalyzed esterification of free fatty acids can also be used for the deacidification of hyperacid vegetable oils. This is useful in the refining of oils to minimize the production of soaps leading to stable emulsions (53). 

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