Determination of colored substances in soybean lecithin

Methods to determine carotenoids, chlorophylls and pheophytins in lecithin by derivative spectrometry were developed. Determinations of those as well as of brown substances were made on commercial soybean lecithins, and the effects of bleaching and powder manufacturing upon color are discussed.     

Composition of soybean lecithin

Commercial soybean lecithin is a complex mixture containing ca. 65–75% phospholipids together with triglycerides and smaller amounts of other substances. The major phospholipids include phosphatidylcholine, phosphatidylethanolamine and inositol-containing phosphatides. Other substances reported include carbohydrates, pigments, sterols and sterol glycosides. This paper reviews the nature of the compounds found in soybean lecithin and our present knowledge of its composition.     

亚硫酸化大豆磷脂的合成研究

通过对大豆磷脂进行酯交换、马来酸酐酯化、中和、亚硫酸化化学改性,合成出亚硫酸化大豆磷脂。研究了改性反应中各因素对反应的影响。得到酯交换反应的较佳工艺条件:70℃下反应1 h,甲醇与磷脂的质量比为11∶100;酯化反应的较佳工艺:催化剂用量为磷脂质量的0.8%,100℃下反应3 h,马来酸酐与磷脂的质量比为13∶100;在亚硫酸化反应中采用碱-NaHSO3/Na2S2O5体系,先中和后亚硫酸化,低温(50℃~60℃)中和,反应结束后升至70℃~80℃,磺化反应程度控制在50%~60%,反应1.0 h~1.5 h。     

Utilization of crude soybean lecithin as a native choline source in feed rations of fattening pigs

In a feeding experiment with six times eight Du x DL-barrows it was tested whether crude soybean lecithin is an useable source for choline in ordinary feed mixtures for fattening pigs. The animals alternatively received diets with 2% soybean oil with or without choline chloride supplement or 1, 1.5, 2, 2.5% crude soybean lecithin, respectively. The groups receiving soybean oil with choline chloride as well as 1.5% soybean lecithin achieved the best fattening performance, but differences in growth and carcass values resp. meat condition were not significant. Lecithin supplements up to 2% in the ration provided an acceptable fat quality with contents of polyunsaturated fatty acids below 15% in carcass fat. The analyzed bloodparameters of the fat metabolism indicated that supplements of soybean lecithin decreased the cholesterol level resp. increased the level of free fatty acids with all parameters within the normal standard. Thus, the results show, that choline chloride as well as soybean lecithin can be used as an alternative source for choline in diets for fattening pigs.     

高纯大豆卵磷脂的制备

采用氧化铝柱层析法,以95%乙醇-氨水(100∶1,体积比)为洗脱剂分离纯化大豆卵磷脂,用高效液相色谱法测定卵磷脂纯度。目的产物纯度93.4%,得率86.6%。为柱层析法工业化生产卵磷脂提供了实验依据。     

Identification of vasopressor phospholipid in crude soybean lecithin

The vasopressor phospholipid in crude soybean lecithin was isolated by column chromatography on Sephadex LH-20. It represented 0.1% of crude soybean lecithin. The isolated phospholipid was identified to be lysophosphatidic acid by gas chromatography-mass spectrometry analysis of TMS-deacylated product and acetolysis product. Nuclear magnetic resonance analysis favored the 1-monoacyl isomer over the 2-isomer. By enzymic determination with L-3-glycerophosphate dehydrogenase, the isolated phospholipid was identified as 1-monoacyl-L-3-glycerophosphate. Gas chromatographic examination revealed that it was composed of a large percentage of unsaturated fatty acids, especially linoleic acid. The activity of isolated lysophosphatidic acid was slightly less than that of synthetic 1-linoleoyl-L-3-glycerophosphate.     

Hydrophobic interactions in the purification of soybean lecithin

Phospholipids have a nonpolar fatty acyl chain and a polar head group, which give them unique physicochemical behavior. They form micellar structures with glycerides, as in the hydration of lecithin, where mixed bilayers of phospholipids and glycerides are formed. In hydrated lecithin, the 70:30 phospholipid/glyceride composition shows the maximum interaction energy and corresponds to the most stable mixed layer. During purification of commercial soybean lecithin (CSL) with acetone, it was observed that the triglyceride extraction curves corresponded to an exponential function shared by the acetone and phospholipid phases. During CSL purification, a fraction of the triglycerides was dissolved, and the rest remained attached to the phospholipids, thus making total separation by simple contact with the solvent impossible. The behavior of these glyceride-phospholipid systems is controlled by such factors as Van der Waals forces, configurational entropy, and alterations in the structure of the adjacent water, similar to the hydrophobic interactions that exist between proteins and lipid chains in biological membranes. In this study, equilibrium plots for the phospholipid/triglyceride/acetone system were obtained and provided evidence of hydrophobic interaction.     

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.     

Fractionation of crude soybean lecithin with aqueous ethanol

Aqueous ethanol was used to fractionate soybean PC and PI, which have dissimilar solubilities in this solvent. The effects of oil and moisture contents of the crude lecithin, ethanol-to-lecithin ratio, and dispersion temperature on the efficiency of phospholipid (PL) fractionation were investigated. Yield, purity, recovery, and PL class composition were examined. Yield was defined as the amount of fractionated material, divided by the acetone-insoluble (AI) matter in the starting material; purity was the percentage of PL (PC+PE+PI) as quantified by HPLC in the fraction; and recovery was the amount of PL quantified relative to the quantity of AI matter. Higher oil contents significantly increased the yield of the PC fraction, but they significantly decreased yield, purity, and recovery of the PI fraction. They also significantly affected the PL composition of the PC fraction. Higher moisture contents significantly decreased the yield but slightly increased the purity of PC fractions. Higher temperatures significantly increased the yield and recovery of the PC fraction. They also affected the relative proportion of PL classes in the PC and PI fractions. The ethanol-to-lecithin ratio significantly affected yield, purity, and recovery as well as the relative proportions of PL in both PC and PI fractions. A combination of multiple fractionation and high-low temperature treatment was also examined. Fractionating twice with ethanol increased the purity of the PC fraction. High-low temperature fractionation increased the purity and PC percentage in the PC fraction.     

离心薄层色谱法提取纯大豆磷脂酰胆碱的研究

采用离心薄层色谱法 (CTLC)提取大豆磷脂酰胆碱 (SPC) ,速度快 ,溶剂消耗量少 ,制备样品量大 ,成本低。研究旨在找到 CTLC的最佳控制条件。产品鉴定采用 HPLC和 TLC,证明产品不含中性杂质和其他磷脂 ,原子吸收测定锌含量质量分数不高于 0 .0 55× 1 0 -6。     

Addition compounds of oxidizing tocopherol and soybean lecithin

Evidence is presented for the formation of addition compounds from tocopherol and soybean lecithin, when adsorbed in monolayer on silica from a mixed solution in chloroform and oxidized at 80 C for 72 hr. Tocopherol was present at 7 mol % of the lecithin in the monolayer. The compounds produced are analogous to linoleic acid-tocopherol adducts previously reported by us. UV spectra of the mixed lecithin and tocopherol monolayers while in silica gel slurry in a solvent were obtained by the method previously reported by us for oxidized linoleic acid and tocopherol monolayers. The monolayer spectra show no evidence for tocopherol dimer. A minor amount of quinone is indicated, but the spectrum has a maximum at 287 nm with no other major peaks. The proposed addition compounds have been characterized by transesterification and hydrogenation, UV, IR, thin layer chromatography and gas chromatography retention behavior, mass spectrometry and elemental analysis. IR spectra of twice-chromatographed addition compounds show specific lecithin absorption bands (5.75 μ; 10.3 μ) together with much enhanced 3.4–3.5, 6.8, 7.25 and 9.14 μ peaks, the latter two being characteristic of α-tocopherol. The UV spectrum of the adducts showed λ _max ^CHCl 3 287 nm, with shoulders at 276 and 300 nm. Hydrogenation removed the peaks at 287 and 276 nm, leaving a peak at 300 nm similar to that of the linoleic acid-tocopherol adduct. Esters of the adducts prepared by transesterification and hydrogenation were similar by all our chemical, chromatographic and spectral tests to the previously characterized esters of the linoleic acid-tocopherol adduct. Paper No. TP-1225 in the U.S. Army Natick Labs. Series.     

Preferential degradation of noncholine phosphatides in soybean lecithin by thermalization

Purified soybean lecithin and the gum derived from soybean oil processing were heated separately in bulk at 125 to 200°C for 60 min, or at 175°C for 30, 60, 90 and 120 min, and the products were analyzed by thin-layer chromatography and high-performance liquid chromatography. It was found that the noncholine phosphatides are preferentially degraded relative to phosphatidylcholine, and that these phosphatides are broken down in the order phosphatidyl-ethanolamine (PE)>phosphatidylinositol (PI)>phosphatidic acid (PA) with increasing temperature. At 175°C, the heating time required to degrade the noncholine phosphatides was between 30 and 60 min. Diglycerides were the principal products of thermalization at 77% of the total material, indicating that the 3-phosphoester linkage is the most heat-labile portion of the noncholine phosphatide molecules. Cleavage of the fatty acids from positions 1 and 2 of the phosphatides was minimal, as indicated by the relatively low amount of free fatty acids (8% of the total) when the lecithin was heated at 180°C for 90 min. The appearance of brown discoloration, characteristic of heated lecithin, coincided mainly with the decomposition of PE.     

从大豆粉末中提取卵磷脂的超声辅助萃取新工艺

采用超声波为辅助手段,以卵磷脂得率为评价指标,用乙醇提取大豆粉末中卵磷脂。结果表明,最佳提取工艺条件为:乙醇浓度为80%,提取温度为40℃,超声时间为50 min,固液比为1∶3.0(g/mL),萃取次数为2次时,可以有效地提取大豆粉末中卵磷脂达12.85%。     

从大豆油脚中提取精制磷脂的研究

本文介绍了从大豆油脚中提取精制磷脂的方法,并讨论了丙酮用量、萃取温度、脱油次数以及活性白土用量、脱色温度等因素对产品质量的影响。得出丁最佳工艺条件,产品收率可达97％左右。     

Fluorescence kinetics of soybean flour oxidation

Changes in fluorescence and oxidation indices of soybean flour were studied during storage at 37, 50, and 60°C. The peroxide value and 2-thiobarbituric acid value did not increase in proportion to the extent of oxidation. The front-surface fluorescence of oxidized soybean flour had an excitation maximum around 350 nm and an emission maximum between 420 and 430 nm. The fluorescent compounds were soluble in the organic phase of chloroform/methanol (2∶1, vol/vol) after addition of water, and the solution showed excitation and emission maxima around 360 and 440 nm, respectively. The fluorescent compounds might have been produced from interactions of oxidizing soybean oil with other constituents of soybean flour. The fluorescence intensity in the organic phase increased steadily throughout the storage period. Fluorescence kinetics of soybean flour oxidation showed a zero-order increase, and the rate followed an Arrhenius relationship with an activation energy of 47.8 kJ/mol. These results suggest that analysis of fluorescence intensity in the organic phase is a useful indicator for determination of the oxidative deterioration of soybean flour.     

从大豆油脚中提取精制脂肪酸的研究

本文介绍了从大豆油脚中提取精制脂肪酸的方法,并讨论了盐酸的质量分数、盐酸用量、回流时间对水解率的影响,得出了最佳工艺条件,最终制成的精制脂肪酸收率可达70％。