Water degumming

Fig. 4 HPLC separation of water-degummed and crude sunflower oil phospholipids on a 250 X 4-mm column packed with Lichrosorb Si-60 according to the AOCS method. The mobile phase consisted of hexane, 2-propanol, and acetate buffer of pH 4.2 in a volumetric ratio of 8/8/1 at 2 ml/min. Detection was accomplished by UV absorption at 206 nm. (Reproduced from Ref. 34 with permission of the American Oil Chemists Society.)...

The phosphatides have polar and nonpolar sites, and generally act as water-in-oil emulsifiers. They are extracted by solvents with the oil, but preferentially will absorb available water, form gums, and precipitate. Commercial lecithin is produced by water degumming (precipitation from oil with ion exchange-treated water) as explained later. 

To prevent hydration and precipitation of phosphatides during storage and shipping, the phosphorous content of crude soybean oil must be reduced to less than 0.02 percent (200 ppm) before entering the trade. This usually is accomplished by water degumming. 

Commercial lecithin is produced by water degumming (precipitation from oil with ion-exchange treated water), separation by stacked disk centrifuge, and vacuum drying to less than 1 percent moisture content. Crude lecithins contain 70-72 percent acetone insolubles (AI) and are standardized to 62-64 percent and an acid value of 30 by addition of oil and fatty acids before sale. Crude lecithins may be treated with acetone to obtain free-flowing powders with 95-98 percent AI. Lecithin can be additionally purified, bleached, fractionated, hydrogenated, hydrox-ylated, acetylated, sulfonated, and halo-genated.104 One domestic company makes 13 kinds of lecithin for food uses alone. 

The organic and natural foods markets demand nonchemically treated oils. These often are made by hard pressing the source and water degumming the oil, followed by bleaching with natural (nonchemically treated) earths and removing FFA by physical refining. 

In the most recent development, acid and aqueous sodium hydroxide, rather than acid and water are being used, especially with lower quality oils (acid-caustic degumming). This represents an intermediate between acid-water degumming and alkali refining. It obviates the need for cooling, similar to the practice in alkali refining. Phosphoric acid rather than an organic acid is preferred in this case. Phosphatides as well as some of the other impurities are removed, and if sufficient, alkali is applied to saponify the free fatty acids, fully refined oil is obtained. 

Typical properties of alkah-refined, bleached canola oil and of acid-water-degummed, acid pretreated, bleached canola oil ready for hydrogenation or steam refining/deodorization are given in Table 16. With the exception of the concentration of free fatty acids, the two process routes produce the same bleached oil quality. 

Phospholipids The phospholipid content of crude sunflower oil ranges between 0.5% and 1.2%. Oils extracted by solvent generally have a higher content of phosphlipids than those obtained by pressing. Major phospholipids are phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidic acid. Most are hydratable and may be removed from the cmde oil through a water-degumming process (See Section 5.3.1.)... 

Crude sunflower oils are produced via mechanical pressing or through extraction with hexane, followed by water degumming. Most oils are stored for relatively long periods prior to refining operations. Cold-pressed crude oils, of superior edible quality, are commercialized as such. Whether unrefined or cold-pressed, the oil may be subject to temperature fluctuations. 

Commercial soybean lecithin is obtained in the traditional manner by hexane extraction of the crude oil from the soybean flake and then water degumming the... 

Nonhydratable phospholipids. According to Myers (138), about 90% of the phospholipids are removed from the oil by water degumming. Although most of the remaining phospholipids are removed by alkali neutralization, Braae et al. (139) report that soybean oil and several other types of vegetable oils often contain some phospholipids that are not removed by alkali neutralization and washing. 

Most seed oils contain 0.2-0.8% nonhydratable phospholipids (5), specifically the magnesium (Mg) and calcium (Ca) salts of phospholipids, which cannot be removed by water degumming. For many years, a common way for nonlecithin producers to degum edible oil was to treat the oil with 0.02-1% of concentrated phosphoric acid at 70-90°C, after water degumming. Then, without the removal of any precipitated solids, the oil is caustically refined. Phosphoric acid chelates the Ca and Mg in the oil so that the nonhydratable phospholipids are converted into the hydratable form. The phosphoric acid pretreatment produces a darker lecithin with lower purity (5). 

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