The processes of degumming, alkali refining, bleaching and deodorization removed 99.8% phospholipids, 90.7% iron, 100% chlorophyll, 97.3% free fatty acids and 31.8% tocopherols from crude soybean oil. The correlation coefficient between the removals of phosphorus and iron in soybean oil during processing was r = 0.99. The relative ratios of α-, β -, γ- and δ-tocopherols in crude oil, degummed oil, refined oil, bleached oil and deodorized soybean oil were almost constant, γ- and δ -tocopherols represented more than 94% of tocopherols in soybean oil. The order of oxidation stability of oil is crude > deodorized > degummed > refined > bleached oil.

Effects of processing steps on the contents of minor compounds and oxidation of soybean oil

The phospholipids (PL), phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were purified from commercial soybean lecithin by silicic acid chromatography and preparative silica gel thin layer chromatography (TLC). Purified phosphatidylinositol (PI) was obtained commercially. Phosphatidic acid (PA) was made from PC by phospholipase D action and purified by preparative TLC. Commercial soybean tocopherols (TOC) were further purified in a florisil column. Combinations of PL and TOC were added to commercially refined, unhydrogenated soybean oil to determine the effects and interaction of PL and TOC on soybean-oil stability. Oil stability was determined by measuring the time in days of oil samples incubated at 110C to reach a peroxide value of 100 meq/kg. Additions of TOC and all PL except PA increased the stability of the oil. PI and PE appear to be more effective than PC in increasing oil stability. The effect of the PL was not simply a matter of pro-oxidant metal inactivation, but rather appeared to extend the effectiveness of the TOC in free-radical termination.

Phospholipids plus tocopherols increase soybean oil stability

Thermal properties and applications of the Arrhenius equation for evaluating viscosity and oxidation rates of unrefined pollock oil

Aqueous enzymatic extraction of corn germ oil was investigated. By applying hydrothermal pretreatment of corn germ, it was possible to inactivate native enzymes present in the germ and to loosen its structure. The corn was then ground and treated with enzymes. After the oil had been released by the enzyme reaction, it was separated by centrifugation. The quality of oil obtained by enzymatic extraction (Pectinex Ultra SP-L at 37°C, pH 5.2, for 6 h) was good. The oil had 1.5% free fatty acids; a total content of oxidation product value of 8.1; light yellow color (AOCS photometric color, 12.7; dominant wavelength λD=575 nm); 0.022% phosphatides; 1350 mg/kg total tocopherol; and an oxidative stability value (Rancimat test, 100°C) of 14.6 h.

Quality of corn germ oil obtained by aqueous enzymatic extraction

Increasing heat treatment given to canola seed prior to pressing resulted in press oils with progressively increasing contents of non-triglyceride components. Phosphorus and chlorophyll contents ranged from 13 ppm and 7 ppm, respectively, in cold press oil to 64 ppm and 68 ppm, respectively, in oil from heated seeds. Refining reduced the amount of these components to 19 ppm and 60 ppm, respectively, in degummed oil and to 4 ppm and 11 ppm, respectively, in bleached oil. Oil with the lowest amount of non-triglyceride material was obtained by cold pressing and/or bleaching.

Effect of heat treatments on canola press oils. I. Non- triglyceride components

This subject deals with the removal of the fat-soluble impurities from crude soybean oil. These impurities may be present in true solution or in a colloidal state; their effective removal is necessary to achieve quality standards for end-use products. The processing step options for the removal of these impurities in any given situation are easily defined; the conditions and practices used, however, are the primary concern of this paper. International trading of soybean oil mandates the degumming step. The increased use of import/export soybean oil increases the importance of this processing practice. Pretreatment and effective contact time are the critical issues. Refining, as a specific process, deals primarily with free fatty acid removal, with or without simultaneous degumming as a single-step operation. State-of-the-art wet, chemical refining practices are described, and the current limitations and future opportunities for the physical refining of soybean oil are discussed. The importance of the bleaching step cannot be overstated and it should be noted that color reduction is only coincidentally achieved. The primary function of the bleaching process is to remove oxidative breakdown products, and the degree or level of treatment should be consistent with that objective. Underbleaching and thermal decolorization (deodorization) of soybean oil are misguided practices. Once “cleaned-up” through adequate bleaching, an oil should be guarded against thermal/oxidative abuse.

L. H. Wiedermann

Papers

Degumming, refining and bleaching soybean oil