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Food Lipids: Chemistry, Nutrition, and Biotechnology

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phospholipid content (phosphorus < 3 ppm) that can be subjected to physical refining<br />

without complex degumming procedures (352,356). The protein recovered by aqueous<br />

enzymatic extraction has higher nutritive/market value than the rapeseed obtained<br />

by conventional pressing followed by solvent extraction; however, the oil yield in<br />

aqueous enzymatic processing is somewhat lower (90–92%) compared with the conventional<br />

process (about 97.5%) (356).<br />

Addition of plant proteases, such as papain or bromelain, to macerated fish<br />

followed by incubation at 65�C for 30 minutes <strong>and</strong> at 50–55�C for 1–2 hours,<br />

respectively, has been shown to improve the recovery of fish oils (372). Thermostable<br />

microbial proteases operating at higher temperatures (70–75�C) appear to be more<br />

suitable for this purpose because they reduce the risk of microbial growth <strong>and</strong> contamination<br />

(107).<br />

B. Enzymatic Degumming of Oils<br />

Degumming is an important processing step during the refining of vegetable oils,<br />

such as soybean <strong>and</strong> rapeseed (canola). Untreated vegetable oils contain varying<br />

proportions of phospholipids (phosphatides), such as phosphatidylcholines (PC),<br />

-inositols (PI), -ethanolamines (PE), <strong>and</strong> phosphatidic acids (PA), which impair the<br />

quality <strong>and</strong> stability of oils if they are not removed. Especially for vegetable oils<br />

that are subjected to physical refining, it is very important to eliminate the phospholipids<br />

prior to treatment of the oil with steam under vacuum for the removal of free<br />

(unesterified) fatty acids.<br />

In the current industrial practice of degumming (373), the raw oils are treated<br />

with water or aqueous solutions of phosphoric acid, citric acid, or an alkali in order<br />

to hydrate the phospholipids that subsequently flocculate <strong>and</strong> thus can be removed<br />

by centrifugation (see also Chapter 8). Among the different classes of phospholipids<br />

PC <strong>and</strong> PI are readily hydratable, whereas both PE <strong>and</strong> PA are hydratable when<br />

combined with potassium <strong>and</strong> unhydratable when complexed with divalent metals;<br />

moreover, PA occurs as a partially dissociated acid <strong>and</strong> is nonhydratable (373,374).<br />

Phospholipase D plays an important role in the formation of nonhydratable PA.<br />

Especially during the processing of soybeans phospholipase D can remain fairly<br />

active even at a temperature of 65�C in the presence of water-saturated hexane,<br />

thereby catalyzing the hydrolysis of hydratable phospholipids, e.g., PC to nonhydratable<br />

PA; however, in aqueous media this enzyme is readily deactivated by heat (375).<br />

Recently, Lurgi AG (Frankfurt, Germany) developed an enzymatic process<br />

(EnzyMax) for degumming of oils that involves treatment of the raw oil with phospholipase<br />

A2 that cleaves the fatty acids esterified at the sn-2 position of the diacylglycerophospholipids<br />

yielding sn-1-acyllysoglycerophospholipids, including sn-1acyllyso-PE<br />

<strong>and</strong> sn-1-acyllyso-PA (Fig. 51), that can be readily hydrated <strong>and</strong><br />

removed (374,376).<br />

Figure 52 shows the flow sheet of the commercial EnzyMax process for degumming<br />

of oils. The enzyme used is a commercially available phospholipase A2 (lecitase activity 10,000 IU/mL) isolated from porcine pancreas. Recently, a microbial<br />

phospholipase A2 that is more economical than the porcine enzyme has been<br />

used successfully for degumming (376). The process consists of three stages. In the<br />

first stage, solutions of citric acid (50% w/v) <strong>and</strong> sodium hydroxie (3% w/v) are<br />

dispersed with the crude oil or water-degummed oil <strong>and</strong> the pH adjusted to approx-<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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