Flavor problems of vegetable food proteins

Flavor is a major factor that limits the use of many vegetable proteins in foods. In high quality whole cereal grains, flavor and flavor stability present little or no problem; but when some cereals are further processed into protein concentrates and isolates, objectionable flavors can arise from oxidative deteri-oriation of unsaturated fatty esters in protein-bound lipids. However, degermed wheat and corn flours (endosperm products) have little or no flavor. Raw legumes and oilseeds enriched with respect to lipoxygenases and other metallo-proteins possess lipid-derived, objectionable flavor compounds. Lipoxygenase-mediated conversion of lipids to lipohydroperoxides and their subsequent degradation form volatile and nonvolatile constituents responsible for off-flavors. n-Hexanal, 3-cis-hexenal, n-pentylfuran, 2(1-pentenyl)furan, and ethyl vinyl ketone are major contributors to grassy-beany and green flavors. Higher 2,4-alkadienals have oxidized painty, rancid flavors sometimes noted in residual lipids. Geosmin, an oxygenated hydrocarbon, is responsible for the musty, moldy, earthy flavor of dry beans. This compound may contribute to similar flavors noted in soy and corn protein isolates. Thermally degraded phenolic acids account for some of the objectionable cooked odors of soy products that have been subjected to high temperature treatment such as retorting, autoclaving, and sterilization. Oxidized phosphatidylcholine most likely accounts for the bitter taste of soy products. Oxygenated fatty acids, including the bittertasting trihydroxy octadecenoic acids, have been identified in the bitter phosphatidylcholines isolated from soybeans. Oxidized lipids appear to be associatted with the bitter, astringent, and rancid flavors of protein isolates prepared from wet-milled corn germ flour. Grassy-beany, bitter flavor compounds preexist in the maturing soybean and are also generated during processing. In some legumes development of off-flavors can be readily controlled by rapid inactivation of lipoxygenase with heat, alcohol, or acid treatment. Legume powders of acceptable flavor quality can be prepared by wet-milling whole seeds in aqueous alcohols. Extraction of meals with hydrogen bond-breaking solvents, such as alcohols or azeotropic mixtures of hexane and alcohol, effectively removes protein-bound lipids to yield concentrates with greatly improved flavors. Soy protein concentrates approaching the blandness of wheat flour have been prepared by a combination of azeotrope extraction and steaming. Similar processes can also be used to greatly improve flavor scores of corn germ protein isolates. Based on our present knowledge about the identity of off-flavor constituents and how they are derived, much progress has been made to effectively remove or modify them. These developments should result in new emerging technology that would be applicable to the manufacture of highly acceptable protein products from various vegetable sources.     

Correlations of flavor score with volatiles of vegetable oils

A simple, direct, gas chromatograph (GC) technique is described for eluting flavor-related volatile components from commercially produced vegetable oils. A sample of oil was placed onto glass wool contained in a GC liner, and the liner was inserted in the heated inlet of the GC. Volatiles from the oils were rapidly eluted by heat and carrier gas onto the GC column. Profiles of the volatiles were obtained by temperature-programmed gas chromatography. Flavor score was highly correlated with individual volatile components considered separately, and very highly correlated with multiple volatile components considered together, indicating that reliable flavor characteristics of vegetable oils may be obtained rapidly and efficiently by instrumentation. Presented at the AOCS Spring Meeting, Mexico City, April 1974.     

Flavor evaluation of copper-nickel hydrogenated soybean oil and blends with unhydrogenated oil

Journal of the American Oil Chemists' Society - Soybean oils hydrogenated to zero linolenate in the pilot plant with a mixed copper-nickel catalyst and a straight copper chromite catalyst were...     

Esterification of high acidity vegetable oil catalyzed by tin-based catalysts with different sulfate contents: contribution of homogeneous catalysis

Biodiesel production costs can be significantly reduced by using nonrefined feedstock. Sulfated solid catalysts have been proposed for producing biodiesel from acid oils by esterification reactions. Nevertheless, leaching of sulfate species to the reaction medium may occur, but often it is not considered. In this article, a commercial tin sulfate (SnSO₄) was used as a catalyst for the esterification of a feedstock with high content of free fatty acid in order to assess the contribution of the homogeneous catalysis in different situations. SnSO₄ was calcined at different temperatures (300, 400, 500 and 700?°C) and converted into SnO₂ after calcination at temperatures higher than 300?°C. Homogeneous catalysis seems possible to occur with all of the catalysts, but it was clearly observed for the uncalcined catalyst (SnSO₄) and for that calcined at 300?°C (SnSO₄(300)). For these catalysts, an important leaching of the sulfate species was confirmed. Higher conversions were obtained with the uncalcined SnSO₄. Reactions at the same conditions using sulfuric acid as catalyst at concentrations of 0.1% were performed and confirmed conversions higher than 80%. Heterogeneous catalysis plays a significant role only with the catalyst that present the highest specific surface areas and acidity (SnSO₄(400)). As some small amount of sulfate species is retained in the structure or surface of the calcined catalysts (even after calcination at 700?°C), we cannot exclude the possibility that these species are also leached during reaction. Thus, a possible contamination of biodiesel through the use of sulfated catalysts cannot be ruled out.     

植物油电化学法合成环氧化合物

采用电化学合成法对植物油进行环氧化合物的合成。通过L_(18)(3~7)正交试验讨论了蓖麻油电化学环氧化的制备工艺条件。采用红外光谱(FT-IR)和热重分析(TG)对植物油及相应环氧化合物的结构进行了表征。实验所得优化工艺条件为:反应时间为4 h,p H=6.5,反应温度为30℃,通氧速率为3 cm~3/s,电流密度为0.3 A/cm~2,蓖麻油双键与HCOOH的摩尔比为8,催化剂(0.1 mol/L盐酸)用量为0.3 m L(相对于40 g蓖麻油),在此条件下所得环氧化蓖麻油相对环氧产率达53.7%。FT-IR分析表明,电化学反应后植物油中-C=C-消失,出现了含有-C-O-C-的新物质;TG分析表明,在一定条件下,-C-O-C-的热稳定性较-C=C-强。这表明植物油电化学法合成环氧化合物是可行的。此外,对大豆油、玉米油和花生油这3种植物油做了同样的验证。     

Catalytic decomposition of vegetable oil

Vapours of crude and prehydrogenated soybean oil were decomposed by passage over solid acid (Al₂0₃⁻n) and base (MgO) in a glass tubular reactor at 300–500°C. The liquid products were analyzed by infrared spectroscopy and gas chromatography.The degree of unsaturation of the oil was found to have a dominant effect on the products. Soybean oil prehydrogenated to a low iodine value of 10 yields essentially pure hydrocarbon products with a mean molecular weight comparable to that of diesel oil, while crude soybean oil yields a mixture of oxygen containing products and hydrocarbons of lower mean molecular weight.These observations were compared to catalytic decomposition of stearic and oleic acids under similar conditions.     

A lamellar liquid crystal with a vegetable oil

The molecular arrangement was studied in the sodium octanoate and cetyltrimethylammonium bromide (CTAB) system, a lamellar liquid crystal, before and after the addition of a vegetable oil [refined, bleached and deodorized (RBD) palm olein] by means of small-angle x-ray diffraction and optical microscopy. Results from the small-angle x-ray showed the RBD palm olein molecules to be partitioned between the nonpolar methyl group layers for both systems. The water molecules, located between the polar head groups, showed less penetrating tendency into the layered structure of cationic surfactant than into the anionic one, both before and after addition of RBD palm olein.     

Rheology of vegetable oil analogs and triglycerides

The rheological properties of two complex mixtures of short-chain triglycerides were experimentally determined. Dynamic or absolute viscosities of the mixtures were measured for shear rates of 0.32 to 64.69 s⁻¹ at temperatures between 25 and 80°C. The compositions of the mixtures were based on the oil of the plant species Cuphea viscosissima VS-320, a natural source of short-chain triglycerides. The dynamic viscosities of these mixtures were compared to those of a traditional vegetable oil (peanut oil) and diesel fuel. The results of this comparison were used to make estimates of the performance of such triglyceride mixtures as diesel fuel substitutes, since viscosity can be a key indicator of fuel performance for possible substitute diesel fuels. The crystallization temperatures of these two mixtures were also determined experimentally, and the effects of crystallization on fuel performance were projected. Additionally, the dynamic viscosities of pure triglycerides from C6∶0 to C18∶0 at 75°C were plotted vs. chain length. These viscosities were measured at high shear rates (>6 s⁻¹) where dynamic viscosity is shear-independent. An obvious trend in the relationship between triglyceride chain length and viscosity was observed. A second-order regression was used to obtain an equation for this relationship. This equation was used as a model for composition dependence of viscosity. This model was applied to the viscosities of the triglyceride mixtures examined here. There was good agreement between the model and the actual, measured viscosity values determined in this study.     

植物油供需市场

概述了印度植物油市场状况,从大豆油、菜籽油和棕榈油市场供需方面深入地进行了分析。重点对棕榈油市场进行了剖析,并对其市场供需状况进行了分析和预测。     

Optimization of industrial vegetable oil hydrogenators

A method to optimize the operation of industrial vegetable oil hydrogenators is proposed. The hydrogenation data from an operating plant are used to fit a simple mathematical model which is then used to select values for temperature and hydrogen pressure such that a desired product is obtained in minimum hydrogenation time, Methodology is suggested whereby any nonoptimal operation can be changed to optimal operation in a few trials.     

Miniemulsion polymerization of vegetable oil macromonomers

The Thames Research Group developed vegetable oil macromonomer (VOMM) technology to combine the advantages of oil-modified polyesters and waterborne systems, and reduce volatile organic compounds in waterborne coatings. VOMMs offer the advantage of temporary plasticization with the potential for crosslinking after film formation. However, incorporating VOMMs into emulsions is challenging because the highly hydrophobic nature of VOMMs restricts their diffusion through the water phase. Miniemulsion polymerization has been used to incorporate highly hydrophobic monomers in waterborne systems. Diffusion limitations are avoided by polymerizing inside the monomer droplets, and to ensure this, droplet stabilization is required. In our study, a soybean oil-based VOMM was used as a copolymerizable hydrophobe in miniemulsion polymerization. Monomer droplets were stabilized prior to polymerization via catastrophic phase inversion to form stable and small droplets (100 nm). Dynamic light scattering analysis was used to confirm miniemulsion stability. A coagulum-free latex was obtained after polymerization. Surface tension studies and light scattering techniques were used to confirm that monomer droplet nucleation was the dominant mechanism. Gel content studies indicated the formation of a highly branched or crosslinked network upon film application. The miniemulsion technique permitted VOMM incorporation as high as 35 wt% into the polymer backbone.     

植物油脚的综合利用

根据国内外油脂化工产业的发展现状,在对植物油脚、植物沥青的成分进行分析研究的基础上提出了植物油脚深加工利用的新研究思路。采用作者所在课题组的研究路线,植物油脚经过综合利用,可得到甘油、二聚酸、异硬脂酸、生物柴油、植物甾醇和天然维生素E等重要化工原料和化学品,利用率可达95%以上。     

Correlation of viscosities of vegetable oil blends with selected esters and hydrocarbons

Blending is often used to reduce the viscosity of vegetable oil lubricants. Experimental rheological results were compared with traditional blending charts and calculation methods. Kinematic viscosities of 90% oleic sunflower, canola, and soybean oils blended with adipates, oleates, polyalphaolefins, and mineral oil were determined at 40°C using capillary viscometers. Blending charts related the viscosities to blend composition with 5% inaccuracy compared with more than 10% deviation made by the cubic equation of Kendall and Monroe. Even more accurate and simpler correlations could be derived. A semilog relationship between viscosities and composition was more accurate than a cubic model. Higher accuracy was also achieved when relating viscosities to volume fractions rather than to weight or mole fractions. Mineral oil blends did not follow the observed rules.     

基于浓度外扰的二维相关近红外光谱快速鉴别4种食用植物油

食用植物油中含有油酸、亚油酸和亚麻酸等不饱和脂肪酸以及脂溶性维生素等,仅仅在含量上有较大差别,因而它们的一维近红外光谱的出峰位置、峰形及峰强度都非常接近。采用基于浓度外扰的二维相关分析结合傅里叶变换近红外光谱(FT-NIR)技术,分析鉴别4种不同食用油。通过对大豆油、葵花籽油、菜籽油、橄榄油在以正己烷为浓度外扰下所得的动态光谱进行二维相关分析,发现4种植物油在4 220~4 310 cm-1波段范围内的二维相关近红外光谱图有明显的差异。表明基于浓度外扰的二维相关近红外光谱能够对食用植物油进行有效的鉴别。