Metal phosphatidates

Like glycolipids, phospholipids are also a elass of polar lipids. Data in Table 3.2 show that phospholipids in natural rubber are normally below 0.6% w/w. A recent study showed that the major components were phosphatidyl choline (PC) and lysophosphatidyl choline (LPC), as shown in Table 3.5. Other minor components were phosphatidyl ethanolamine (PE), phosphatidyl inositol (PI), lysophosphatidyl inositol (LPI), and metal phosphatidates (MP) or phosphatidic acid (PA). Unlike neutral lipids and glycolipids, the acyl components of phospholipids normally contain very low levels of furanoic acid, except for certain rubber clones. The isolated fatty acids are mainly palmitic, stearic, oleic and linoleic acids. ... 

Cmde oils from these processes are often of insufficient quaUty to be used directly, particularly for edible products. Impurities such as pigments, phosphatides, volatile odorous compounds, and certain metals must be removed by further processing. 

The valency of the metal ion changes in every step so that a single atom of heavy metal (Me) may produce many free radicals. Metal chelating compounds, such as citric, tartaric or phosphoric acids, ascorbic acid, phytin or phosphatidic acids, combine with metals to form non-reactive compounds so that the oxidation reactions are inhibited and natural food antioxidants are saved. 

Ethanolamine, pKa value of 99 Ethanolamine ammonia-lyase 871 Ether lipids 382 Ether phosphatides 383s Ethidium 223s Ethidium bromide 221, 222 Ethylenediamine, binding constants to metal ions 311... 

Albumin is the main plasma protein, with a molecular weight of about 69 kDa, and is important for normal plasma oncotic pressure and the transport of many biologically active substances, including free fatty acids, phospholipids (e.g., lysophosphatidic acid), prostanoids, heavy metals, steroid hormones, and vitamins. Albumin-bound lysophosphatidic acid serves as a survival factor for cultured mouse proximal tubular cells (L4). Lysophosphatidic acid is an exquisitely potent inhibitor of apoptosis, comparable with growth factors, for example, EGF. The influence of lysophosphatidic acid on the survival of tubular cells depends on the activation of phophatidylinositol 3-kinase (PI3K) with subsequent activation of Akt and pp70s6k. pp70s6k is a rapamycin-inhibited kinase, which plays an important role in the cellular proliferation. Lysophosphatidic acid also serves as a proliferation factor of mouse proximal tubular cells. Further albumin-bound factors important for the survival of the proximal tubular cells are phosphatidic acid... 

Refining involves the purification of triglyceride to remove impurities (phosphatides, polyethylene, chlorophyll, heavy metals, off-odors, color bodies) by a combination of acid/alkali washing, clay/activated silica bleaching, deodorization, and hydrogenation steps. 

A typical fat refining plant (Alfa-Laval process) for the acid washing of fats and oils is illustrated in Fig. 36.8.8 The triglyceride is degummed to remove phosphatides and other impurities such as mucilage, proteinaceous matter, and trace metals by acid washing with citric or phosphoric acids, and then is sent to a bleaching plant where it is dehydrated and treated with an activated clay for the removal of color bodies, heavy metals, chlorophyll, and polyethylene (Fig. 36.9).6... 

Hydrogen peroxide has been used to bleach soya beans,171 lechitan and phosphatides.172 The alkali metal peroxides are alternative reagents.173 It is also used to decolorize fatty acid sarcosides,174 whilst xanthines require sodium perborate or percarbonate175 and starches require some irradiation.176... 

Bleaching. The refined oils are usually dark in color owing to the presence of some pigmented materials such as chlorophyll or carotenoids and minor impurities like residual phosphatides, soaps, metals, and oxi-datin products. Bleaching reduces the color by absorbing these colorants on bleaching earth (bentonite clays), or activated charcoal, or both. In addition to decolorization, bleaching clay also absorbs suspended matter and other minor impurities. 

Refining of crude fats and oils involves a series of steps for the removal of impurities from the glycerides to make the product suitable for human consumption and improve product shelf life. The impurities are fatty acids, phosphatides, metal ions, color bodies, oxidation products, solid paricles, and volatiles that include objectionable odors. Crude coconut oil is refined by any of the following methods (1) chemical refining (batch or continuous) and (2) physical refining. The comparative performance of both methods is summarized in Figure 4. 

The main feature in physical refining of crude oils is the application of steam distillation to remove the free fatty acids and volatile components from the oil. The technical feasibility of physical refining depends largely on the pretreatment stages for the removal of phosphatides, color bodies, metal ions, and nonvolatile impurities. Without an effective pretreatment, steam refining may fail to produce an oil of color and stability characteristics comparable to the classically refined product (23). 

Crude Oil Conditioning—Crude oils with high levels of phosphatides and trace metals are usually treated with food-grade phosphoric acid for 4 to 8 hours before refining. The purpose of the acid pretreatment is to (1) help precipitate phosphatidic materials (2) precipitate natural calcium and magnesium as insoluble phosphate salts (3) inactivate trace metals, such as iron, copper, and others that may be present in the oil (4) reduce the neutral oil losses and (5) improve the color and flavor stability of the finished deodorized oil. 

In the fractionation process, the minor components of the original oil become concentrated in the separated fractions. This concentration has a considerable effect on the oxidative stability of the individual fractions. Relative to the starting oil, the liquid or soft fraction is enriched in tocopherols and depleted of trace metals. The reverse occurs with the hard or stearine fraction, which becomes appreciably more susceptible to oxidation despite its lower content of unsaturates. The stearine fraction is also the recipient of other impurities remaining in the oil after rehning and bleaching, such as phosphatides and soap. 

Caustic refining in particular does not only effectively perform the separation functions described above but is considered more forgiving in operation than alternate physical methods. If the degumming operation has been less than perfect (or is not used), alkali refining will remove the bulk of the phosphatides. If a high amount of metals, particularly calcium and magnesium, are present, these can be... 

Pigments Oxidation Products Residual Phosphatides Residual Metals Soaps... 

Free Fatty Acids Phosphatides Metals Soaps Some Pigments... 

It prepares the oil for physical or steam refining—degumming significantly reduces the nonvolatile phosphatides and metallic prooxidants. 

Silicates—These chemically inert synthetic amorphous silica adsorbents have an affinity for polar contaminants. The surface area, porosity, and moisture content of the silica adsorbents provide them the capability of adsorbing secondary oxidation products (aldehydes, ketones), phosphatidic compounds, sulfur compounds, trace metals, and soap. Moisture functions to hold the pores open and aid in the attraction of the polar contaminants. Most of the synthetic silicas do not have significant direct adsorption capabilities for carotenoid or chlorophyll compounds, but the removal of the other impurities enhances the efficiency of the bleaching earths (Young, 1990). 

A membrane-derived a-amylase was solubilized from membrane vesicles by treatment with Triton X-100 and was highly purified by chromatography on an anti-a-amylase-protein A-Sepharose column. Membrane-derived a-amylase was indistinguishable from the soluble extracellular enzyme by sodium dodecyl sulphate-gel electrophoresis and radioimmunoassay. The membrane-derived enzyme contains phospholipid. Approximately 30 to 80% of the phospholipid was extracted from the purified enzyme by chloroform-methanol. The extracted phospholipid was predominantly phosphatidylethanolamine. Treatment with phospholipase D released phosphatidic acid. Membrane-bound a-amylase was latent in membrane vesicles. Release of membrane-bound a-amylase from vesicles by an endogenous enzyme was maximal at pH 8.5, was inhibited by metal chelators and di-isopropyl fluorophosphate and was stimulated by Ca and Mg. The amount of membrane-bound a-amylase was related to the level of secretion. 

Oil suitable for deodorization must be free of impurities that can undergo rapid heat degradation and which can impair the flavor and color stability. The following are notable phosphatides, which should not exceed 5 ppm as phosphorus equivalent chlorophyll and derivatives, which should be essentially undetectable, and nickel, which should be below 0.5 ppm. Further, the prooxidant metals iron and copper should not exceed 0.1 and 0.01 ppm, respectively (Evans et a/., 1951). 

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