Egg-yolk lipid fractionation and lecithin characterization

Egg-yolk lecithin has phospholipid (PL) classes and a FA composition that differ from soybean lecithin and may have unique functional properties. The purposes of this research were to develop an effective method for extracting a sufficient amount to lecithin from fresh egg yolks and to evaluate its functional properties. Ethanol was used to dehydrate and partially extract the PL, after which hexane was used to extract the total lipids. A phase separation of the combined extracts resulted in neutral and polar lipid fractions. An acetone precipitation of PL from the final polar lipid fraction was necessary to remove the residual neutral lipids, especially cholesterol. The purity of PL in the lecithin product was 95%. Surface tension reduction, emulsion stability, and oxidative stability studies were conducted to characterize the functional properties of egg-yolk lecithin. Egg-yolk lecithin and soy lecithin had similar surface activities, as evaluated by the surface tension reduction in an aqueous system and the critical micelle concentration. Soybean lecithin created a more stable emulsion than egg-yolk lecithin. However, egg-yolk lecithin was more oxidatively stable than soybean lecithin.     

Effect of lecithins partly replacing rumen‐protected fat on fatty acid digestion and composition of cow milk

The effects on fatty acid digestibility and milk fat composition of calcium soaps of palm oil fatty acids and of a 25% replacement of the Ca soaps by four different lecithins (raw, deoiled and deoiled/partially hydrolysed soy lecithin, raw canola lecithin) and soybean oil were investigated in six lactating cows each. The complete diets contained the lipid supplements at proportions of 30 g fatty acids/kg dry matter. Partial replacement of Ca soaps by soy or canola lecithins and soybean oil had small but significant effects on fatty acid digestion and utilisation, as well as the fatty acid profile in milk. Relative to Ca soaps alone, C 16:0 digestibility was slightly higher with lecithins, and percentage of conjugated linoleic acid and trans C 18:1 in milk fat increased while proportion of C 16:0 decreased. Deoiling of lecithins slightly reduced the effects on C 16:0 digestibility and excretion with milk. The influence of lecithin processing was higher than the differences between raw soy and raw canola lecithin. Nevertheless, most of the few effects observed may be related to the fatty acids supplied with the lecithins but, regarding C 18:1 trans‐11 and odd chain fatty acids, there is some evidence that lecithins impair rumen microbial activity less than soybean oil.     

Antioxidant effect of soy lecithins on vegetable oil stability and their synergism with tocopherols

The antioxidant effect of lecithins was tested on several oils and fats varying in FA composition and tocopherol content. Standard lecithins, when added at a level of 1% w/w, exhibited a good protective effect against oxidation. This effect was observed to depend on the phospholipid content of the tested lecithins and the FA composition of the tested oils. Better results were obtained with lecithin samples containing high proportions of PC and PE. Indeed, the main antioxidant mechanism of lecithins was due to a synergistic effect between amino-alcohol phospholipids and γ- and δ-tocopherols. No synergism was observed with α-tocopherols, especially when the tested oil was rich in linoleic acid. Therefore, the antioxidant protection of lecithins was not effective for sunflower oil. Finally, the use of fractionated or enriched lecithins was not clearly advantageous compared to standard oil lecithins.     

Lecithins in oil-continuous emulsions. Fat crystal wetting and interfacial tension

Lecithin is a powerful emulsifier widely used in foods, feeds and pharmaceuticals. Several analytical methods have been proposed to characterize lecithins, but they are often inadequate to determine the industrial functionality. The purpose of this study was to find a relationship between the interfacial properties of lecithins (adsorption to oil/water and fat crystal/oil/water interfaces), phospholipid composition and functionality. Results show that all lecithins adsorb to fat crystals at the triglyceride oil/water interface, making their surface more polar (observed as an increase in the contact angle measured through the oil at the interface: fat crystal/oil/water). This adsorption process is quick (less than five minutes) for relatively polar lecithins, such as soybean phosphatidylcholine (PC), and results in highly polar surfaces (contact angle ∼180°). Less polar lecithins give slow adsorption (some hours) and less polar crystals (contact angle ≤90°). The adsorption of different lecithins to the oil/water interface, observed as a decrease in interfacial tension, follows the adsorption pattern to the fat crystals. We found a relation between high-fat crystal polarity and poor lecithin functionality in margarine (margarines spatters during frying), and also between high-fat crystal polarity and a high polar to nonpolar phospholipids [Σ(PI + PA + LPC)/ΣPE; PI, phosphatidylinositol; PA, phosphatidic acid; LPC, lysoPC, PE, phosphatidylethanolamine] ratio in lecithin. The correlations might bevia aggregation properties of lecithin in the oil. We found also that monoolein shifted the adsorption kinetics of lecithin (soybean PC) to fat crystals and the hydrophilicity of adsorbed layers probably due to formation of mixed aggregates between monoolein and soybean PC.     

Compositions of commercial corn and soybean lecithins

The lipid and fatty acid compositions of commercial corn and soybean lecithins were compared. The types of lipids were similar, but the proportions varied. The ratio of glycolipids to phospholipids was 0.36 for corn lecithin and 0.14 for soybean. Phosphatidylcholine and phosphatidylinositol were major phospholipids in both lecithins. In soybean lecithin, the percentage of phosphatidyleth-anolamine equaled that of phosphatidylinositol, but in corn, the percentage of phosphatidylethanolamine was only about one-fourth the percentage of phosphatidylinositol. High levels of phosphatidic acid in both the corn and soybean preparations indicated some degradation of the phospholipids during processing. The major differences in fatty acid compositions were a higher percentage of oleic acid and lower percentages of stearic and linolenic acids in corn compared to soybean. The lower level of linolenic acid should give corn lecithin greater resistance toward autoxidation and the development of off-flavors.     

Laboratory Studies on Membrane Deoiling of Lecithin

Deoiling of lecithin using a nonporous membrane was examined in a favorable solvent (hexane) medium with soy and rice bran lecithins. During the membrane process, the acetone insoluble (AI) content of soy lecithin increased from 63.2 to 81.0% in a single step batch operation. The membrane exhibited an excellent selectivity since phospholipid (PL) reverse micelles formed in the system were rejected almost completely due to low solubility probably aided synergistically by size exclusion. Diafiltration achieved greater oil removal from lecithin as reflected in terms of higher AI and PL contents in the deoiled lecithin. In discontinuous diafiltration, the PL content increased from 33.3 to 85.5% in rice bran lecithin (150% dilution to feed) and 56.6 to 85.7% in soy lecithin (200% dilution), respectively. The simulated continuous diafiltration run showed slightly greater PL content in soy lecithin (91.3%) compared to discontinuous diafiltration (89.7%) besides offering higher productivity. The membrane showed a color reduction of ~60% in soy lecithin but there was no improvement in rice bran lecithin due to the retention of degradation products. The proposed integrated membrane process with nonporous (deoiling) and nanofiltration (solvent recovery) membranes could be an attractive preposition besides being an acetone free process.     

Toolbox for modification of the lecithin headgroup

In an effort to produce structurally divergent lecithins for testing of their functional properties and use in food products, several tools have been developed to carry out modifications in the polar head group distribution of the native phospholipids in soybean lecithin. These tools include physical, chemical and enzymatic techniques. Using a combination of acetone de‐oiling, ethanol fractionation, N‐acetylation and enzymatic hydrolysis and transphosphatidylation with a phospholipase D from Streptomyces sp., a set of lecithins with modified head group distributions were produced. The kinetics of the enzymatic head group hydrolysis and transphosphatidylation was studied in detail. Reaction rates and selectivity (transphosphatidylation / hydrolysis) were affected by both lecithin concentration and donor alcohol concentration. Hydrolysis, forming phosphatidic acid, was strongly dependent on both concentrations, whilst transphosphatidylation, forming phosphatidyl glycerol (or phosphatidyl ethanolamine or phosphatidyl serine), was only influenced by the donor alcohol. This resulted in a reduction in selectivity at high initial lecithin concentrations and suggested the use of a reactant feeding strategy. Enrichment of the phosphatidyl choline content of native soybean lecithin was achieved by ethanol fractionation and phosphatidyl inositol enrichment was by N‐acetylation with acetic anhydride followed by de‐oiling. The application of these tools, together with others designed to modify the fatty acid composition of phospholipids, was used to produce 10‐100 g quantities of divergent lecithins and can be routinely used at lab‐scale.     

Influence of dietary soybean and egg lecithins on lipid responses in cholesterol-fed guinea pigs

The comparative influence on plasma and tissue lipids of dietary soybean and egg lecithins, which have contrasting fatty acid compositions, was studied in the hypercholesterolemic guine apig. The polyunsaturated to saturated fatty acid (P/S) ratios of the soybean and egg lecithins were 3.4 and 0.38, respectively. Hypercholesterolemia was induced by feeding guinea pigs a purified diet that contained 15% lard enriched with 0.5% cholesterol. Subsequently, guinea pigs were fed for six wk the same diet supplemented with either soybean or egg lecithin as 7.5% of the diet. A control group continued to be fed the lecithin-free diet. Parameters measured included body weight and relative liver weight; in plasma, total cholesterol, high density lipoprotein cholesterol (HDLC), phospholipid, and nonesterified cholesterol; in liver, total fat, cholesterol, and the specific activity of the catabolic enzyme cholesterol 7α-hydroxylase; (EC 1.14.13.17); and in the aorta, cholesterol. Among the most noteworthy observations were the 49% decrease in total plasma cholesterol of the soybean lecithin group without decreasing HDLC and the 177% increase in HDLC of the egg lecithin group without a significant increase in total cholesterol compared with those values in the control group. These data suggest that dietary lecithin is particularly effective in increasing the HDLC/total cholesterol ratio in plasma. However, the absolute concentrations of those plasma lipids seem to depend upon the fatty acid composition of the lecithin. Presented in part at the annual meeting of the American Oil Chemists' Society, New Orleans LA, May 1987.     

Phospholipids of environmentally stressed soybean seeds

Protein and oil content of the soybean [Glycine max (L.) Merr.] seed and the fatty acid composition of the oil can be altered by environmental stress. The objective of this study was to characterize the composition of the phospholipid (PL) from soybean seeds after exposure to drought and high temperature during seed fill. Drought stress was imposed on greenhouse-grown soybean plants at temperatures of 28 and 33‡C after the beginning of seed fill and was maintained throughout the seed-fill period. The fatty acid composition of each PL class was altered by drought and high temperature. With phosphatidylcholine and phosphatidylethanolamine, which composed 89% of the separated PL, greater proportions of 16:0 and 18:0 and lesser proportions of 18:2 and 18:3 were present in soybean seeds exposed to high temperature and severe drought. More linolenic acid and less palmitic acid were present in phosphatidylinositol. The changes were comparable to those of the triglyceride because of high temperature. The elevated temperature increased the proportion of phosphatidylcholine and phosphatidylinositol and decreased that of phosphatidylethanolamine. The effect of drought and high temperature stress on PL class and fatty acid composition has important implications on the quality of soybean seed oil and lecithin and on the ability of the seed to maintain optimum rates of metabolism in the development and germination environment.     

Indian ricebran lecithin

In view of the high potential of ricebran oil in India, lecithins recovered from crude and dewaxed Indian ricebran oil were analyzed and different classes characterized with the objective of effectively utilizing this valuable by- product. Lipid classes and individual phospholipid components were identified and estimated. Dewaxing was found to have a considerable effect on composition of the derived lecithin. The lecithin obtained from crude or dewaxed Indian ricebran oil consisted mainly of phosphatidylcholine, phosphatidylethanolamine, phosphatidylnositol and triglycerides, along with carbohydrates, free fatty acid, sterols and waxes (in case of crude oil). The major fatty acids of individual phospholipids were found to be palmitic, oleic and linoleic. Analytical characteristics of ricebran lecithin were shown to be comparable to local soybean lecithin. It can be expected that the gummy materials in the oil, presently lost with the soapstock during refining, could find important applications.     

The function of phospholipids of soybean lecithin in emulsions

A number of commercially available soybean lecithins were analyzed with respect to their phospholipid composition and emulsifying properties. A phosphatidylcholine (PC) from soybean swells to a lamellar liquid crystalline phase which incorporates slightly less than 50% of water. The swelling behavior of the commercially available soybean lecithins may be different depending on the concentration of other phospholipids such as phosphatidylethanolamine (PE), phosphatidylinositol (PI) and phosphatidic acid (PA). In the presence of the negatively charged phospholipids PI and PA, the swelling of the lamellar phase of PC was dramatically enhanced while a lecithin with equal amounts of PC and PE and small quantities of PI and PA formed two liquid crystalline phases, i.e., a lamellar and a hexagonal phase. Stable o/w-emulsions can be prepared when the phospholipid composition is such that a lamellar liquid crystalline phase in equilibrium with the oil and water phases incorporates large amounts of water. The minimal amount of emulsifier required to stabilize the emulsions has been estimated to give an interfacial film of ca. 80 Å thickness which corresponds to a thickness of two double lipid layers in the interfacial film. The incorporation of large amounts of water is obtained if the lamellar layers contain dissociated ionic groups.     

Determination of the structure of lecithins via the formation of acetylated 1,2-diglycerides

A detailed procedure for quantitative determinations of molecular species of lecithins is described and applied to several lecithins isolated from natural sources. The method is based on the conversion of lecithin to acetylated 1,2-diglycerides and analysis of these compounds by methodology used for the determination of triglyceride structure. The preparation of the acetylated 1,2-diglycerides was carried out via hydrolysis with phospholipase C and acetylation of the resultant, 1,2-diglycerides with pyridine-acetic anhydride. Preparation of acetylated 1,2-diglycerides from lecithin by acetolysis with acetic acid-acetic anhydride was shown to be accompanied by intermolecular as well as intramolecular rearrangement of the fatty acids. The structure of the acetylated 1,2-diglycerides was determined by a combination of argentation-TLC and pancreatic lipase hydrolysis using internal standards for quantification. The method was applied to lecithins isolated from milk serum, egg, soybean, safflower seed and wheat germ lipids.     

31P nuclear magnetic resonance phospholipid analysis of anionic-enriched lecithins

Phosphorus-31 nuclear magnetic resonance provides well-dispersed, quantifiable phospholipid profiles of commercial and laboratory anionic lecithin preparations. Seventeen phospholipids were determined in commercial soybean lecithins. Lecithin refinement to produce anionic-enriched lecithins may be monitored precisely.     

Effects of expander process on the phospholipids in soybean oil

Crude oils were extracted from soybean flakes and collets by conventional and expander processes, respectively. The phospholipids were removed by degumming, and the lecithins were produced by using commercial procedures. The effects of the expander process on the degumming efficiencies were evaluated. The differences in the phosphatide compositions of the oils and the lecithins produced from expander and conventional processes were compared by high-performance liquid chromatography. The phosphorus content indicated that expander-processed oil contained more phosphorus (985 ppm) than the conventional oil (840 ppm). However, the phospholipids in the expander-processed oil were more hydratable than those in the conventional oil. After degumming, the phosphorus content in the expander-processed and conventional oil were reduced by 93.2 and 78.6%, respectively. The expander-processed lecithin contained 74.3% acetone-insoluble matter (AI), and the conventional lecithin contained 65.8%. More phosphatidylcholine was found in the expander-processed lecithin (39.78%, based on AI) than in the conventionally processed lecithin (34.19%). The phosphatidylinositol contents of the expander-processed lecithin and the conventional lecithin are almost the same (19.95 and 19.97%). The phosphatidylethanolamine in the expander-processed lecithin (12.36%) was lower than that in the conventional lecithin (18.07%).     

Polymorphic and microstructural behaviors of palm oil/lecithin blends crystallized under shear

There has been much work on polymorphism and crystal habit of quiescently crystallized palm oil. However, researchers have found it difficult to probe the process of sheared crystallization. The effect of surface-active molecules as nucleation agents or habit modifiers was demonstrated in quiescent systems. The aim of this work is to explore the effects of shear and specific lecithins (soy and sunflower) on palm oil crystallization by monitoring crystallization under shear using a synchrotron radiation source, as well as microscopy and DSC. It was found that increasing shear led to increasing β′ stabilization in all situations. Soybean lecithin had little effect on behavior. Sunflower lecithin led to even greater β′ stabilization. The different lecithins interact with the crystallizing fat changing rates of nucleation and crystal growth. Thus, the structure of the overall system can be dramatically altered. Microscopy revealed very different structures even if the polymorphism of the different systems was similar. Consequently, specific interactions can be manipulated in order to control the system. In particular, control of lecithin composition affects the stability of the different polymorphs. Palm oil crystallization under realistic processing conditions has been characterized. Under these conditions, increasing shear rates give higher β′ stability. Specific lecithins have different effects. In particular, soybean lecithin is β′ stabilizing, whereas sunflower lecithin has limited effects. Thus the overall structure of lecithin is important in determining the efficacy. This can be applied to control the structure and properties of different systems such as shortenings or spreads where crystalline interactions create the macro-structure that determines product properties.     

Hypolipidemic Effects of Phospholipids (PL) Containing n-3 Polyunsaturated Fatty Acids (PUFA) Are Not Dependent on Esterification of n-3 PUFA to PL

Phospholipids (PL) containing n‐3 polyunsaturated fatty acids (PUFA) have beneficial effects of maintaining and promoting health compared with triacylglycerols (TAG) containing n‐3 PUFA or general PL. This study evaluated the effects of dietary PL containing n‐3 PUFA and elucidated the effects of the glycerophosphate structure and n‐3 PUFA on fatty acid (FA) metabolism in rats. Rats were fed a basal diet containing soybean oil alone, TAG containing n‐3 PUFA (1.8 %), soybean PL (2.7 %), PL containing n‐3 PUFA (2.7 %), or TAG containing n‐3 PUFA (1.8 %) + soybean PL (2.7 %). The present n‐3 PUFA‐supplemented diets had similar FA compositions, and the PL diets had similar PL compositions. TAG containing n‐3 PUFA reduced serum TAG contents, but did not affect serum cholesterol contents compared with soybean oil alone. PL diets containing n‐3 PUFA and the combination of TAG containing n‐3 PUFA and soybean PL resulted in decreased serum and liver TAG contents compared with the diet containing soybean oil alone, reflecting enhanced liver FA β‐oxidation. The results of this study show that TAG containing n‐3 PUFA with added soybean PL affects serum and liver TAG and cholesterol contents to a similar degree as PL containing n‐3 PUFA. TAG containing n‐3 PUFA and soybean PL are widely used as functional food ingredients and pharmaceutical constituents and are inexpensive compared with PL containing n‐3 PUFA. Therefore, the combination of TAG containing n‐3 PUFA and soybean PL has potential as a useful and inexpensive component of functional foods.     

Analysis of soybean lecithin by thin layer and analytical liquid chromatography

The application of thin layer and analytical liquid chromatography to the analysis of two samples of commercial soybean lecithins is described. A combination of column chromatography and quantitative thin layer chromatography showed that these products consisted of ca. 82% mixture of the major phospholipids of soybeans, phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidyl inositol. The remainder of these products contained essentially the entire spectrum of lipid classes found in soybean oil-some 24 known and unknown glycolipids and phospholipids, in addition to the neutral lipids. Applications of analytical liquid chromatography to these lecithins gave a composition profile of the lipid classes comparable to two-dimensional thin layer chromatography. The potential of this method for the complete analysis of complex lipids, such as soybean lecithins, is indicated.     

Cross-Sectional Associations of Food Consumption with Plasma Fatty Acid Composition and Estimated Desaturase Activities in Finnish Children

Plasma fatty acid (FA) composition is known to be an indicator of dietary fat quality, but the associations of other dietary factors with plasma FA composition remain unknown in children. We investigated the cross-sectional associations of food consumption with the proportions of FA and estimated desaturase activities in plasma cholesteryl esters (CE) and phospholipids (PL) among children. The subjects were a population sample of 423 children aged 6–8 years examined at baseline of The Physical Activity and Nutrition in Children (PANIC) Study. We assessed food consumption by food records and plasma FA composition by gas chromatography. We used linear regression models adjusted for age, sex, physical activity and total energy intake to analyze the associations. A higher consumption of vegetable oil-based margarine (fat 60–80 %) was associated with a higher proportion of linoleic and α-linolenic acids in plasma CE and PL. A higher consumption of high-fiber grain products was related to a lower proportion of oleic acid in CE and PL. The consumption of candy was directly associated with the proportion of palmitoleic and oleic acid in plasma CE. The consumption of vegetable oil-based margarine was inversely associated with estimated stearoyl-CoA-desaturase activity in plasma CE and PL and the consumption of candy was directly related to it in plasma CE. The results of our study suggest that plasma FA composition is not only a biomarker for dietary fat quality but also reflects the consumption of high-fiber grain products and foods high in sugar among children.     

Positional Distribution of Fatty Acids in Oilseed Lecithins

Positional distribution of fatty acids in the lecithins (phosphatidyl choline) of cottonseed, groundnut, mustard and sesame seeds was studied. GLC analysis of the methyl esters showed the total lecithins to contain 60–80% of unsaturated fatty acids. The fatty acids liberated by phospholipase A hydrolysis consisted mainly of unsaturated (oleic and linoleic) acids. Estimates of lecithin classes in terms of saturated and unsaturated fatty acids in the α- and β-position, viz. SS, SU, US and UU, were made in these lecithins. The amount of disaturated (SS) lecithin was negligible and the content of US species was very low. Mustard, sesame, groundnut and cottonseed lecithins contained 27, 47, 56 and 60% of SU species respectively. The diunsaturated (UU) lecithin content was high in mustard (69%) and medium in sesame (49%), groundnut (43%) and cottonseed (31%).     

The Composition and Properties of Purified Rapeseed Lecithins

The chemical and physical parameters of various quality grade rapeseed lecithins obtained from raw lecithin and from lecithin wet gum were evaluated. The chemical composition, fatty acids and metals contents, acid, peroxide and iodine values were determined. From the data it could be suggested, that the purified rapeseed lecithins obtained from 00-varieties, especially prepared directly from rapeseed wet gum are the interesting and valuable material for use in pharmacy, food industry and cosmetics.