Nonhydratable phosphatides

Some natural nonhydratable phosphatides always are present in crude oil, but development of additional NHP during seed extraction can be minimized by heat inactivation of phospholipases as explained earlier. In preparation for degumming, a tank large enough to supply the refinery with uniform oil feed... 

The objective in acid degumming is to chelate the calcium and magnesium ions and render the nonhydratable phosphatide forms hydratable. In addition to phosphoric acid, citric and malic acids are effective, as well as eth-ylenediaminetetraacetic acid (EDTA). Acid-treated phosphatides are not used for production of commercial lecithins. Extensive reviews on oil degumming have been prepared.106 107 Lurgi, a German equipment manufacturer, has developed an EnzyMax process that cleaves the nonhydratable phosphatides with a phospholipase B at the triglyceride s second carbon to produce a lysophosphatide that is insoluble in oil and is removed by centrifuging.108... 

The crude oil from which gums are taken for lecithin production still contains nonhydratable phosphatides, but can be treated with a chelating agent before alkali neutralization and will be removed with the soapstock by centrifugation. Provision must be made for the added acid in calculating the amount of neutralizing alkali added. 

Peroxide Value, Fats and Oils (PV) (Cd 8-53) determines all substances, in terms of milliequivalents of peroxide per 1000 g of sample, that oxidize potassium iodide (KI). These substances generally are assumed to be peroxides or products of fat oxidation. Phosphorus in Oils (Ca 13-55) estimates the phospholipid content of crude, degummed, and refined vegetable oils in terms of phosphorus. Refineries often use induction coupled plasma (ICP) spectrographs to analyze divalent cations rapidly in aspirated crude oil. The calcium and magnesium measured are mainly responsible for nonhydratable phosphatides (NHP) and are determined directly. An AOCS method for analysis by ICP is being developed. 

A whole variety of processes have been developed to improve the removal of the nonhydratable phosphatides. The best known are the uni-and superdegumming processes (unilever) and the TOP degumming process (vandemoortele). They are principally based on a special acid treatment of the NHP. Over the last few years, several new technological approaches have been developed, which guarantee very low levels of phosphorus (less than 10 ppm). 

In the soft-degumming process, a chelating agent (EDTA) is added to the oil to remove the cations from the nonhydratable phosphatides, thereby making them hydratable again (Table 4.11) [4]. 

Cooking also inactivates two key enzymes. The first is myrosinase, which hydrolyses glucosinolates into oil-soluble sulfur-containing compounds. The second is phospholipase, which hydrolyses phospholipids into nonhydratable phosphatides. Myrosinase activity has been extensively studied and is carefully controlled during the cooking operation that minimizes hydrolysis of glucosinolates and reduces... 

Residual phosphatide concentrations are from 5-50 mg/kg of phosphorus depending on process details and the level of nonhydratable phosphatides in the crude oil. Nonhydratable phosphatides can vary widely, but are usually in the range of 20-45% of total phosphatides. With higher concentrations of nonhydratable phosphatides, longer agglomeration time is required to achieve clean separation in the centrifuge. 

TABLE 17. Content of Total Phosphatides (TP) and Nonhydratable Phosphatides (NHP) of Crude Sunflower Oil [Based on (67)]. 

The use of expanders does have an impact on the quality of the oil that the integrated processor should be aware of. An interesting phenomena of the expander is that while phosphorous levels in the extracted crude oil are normally increased over traditional flake extraction (typically as much as 200 ppm as P in soybean oil), nonhydratable levels in the degummed oil are normally lower. It is postulated that partial inactivation of the lipase enzyme (blamed for conversion of nonhydratable phosphatides) occurs in the expander and, while the crude oil has a higher neutral oil loss, the quality of the degummed oil is higher. In fact, one processor reported that despite aU efforts to make a soybean oil physical refining plant function, the oil was of substandard quality until the plant installed expanders. Once installed, the plant could consistently produce a quality physical refined oil (4). 

Wet extmders are also used ahead of a number of soybean solvent extraction plants. In plants with undersized extractors, the energy used by the extruder can be compensated by additional oil yield from the extractor. Steam consumption is reduced in the desolventizer toaster. Additionally, the wet extruder in a soybean plant increases temperature sufficiently to stop the phospholipase enzyme from converting additional hydratable phosphatides into nonhydratable phosphatides. This reduces acid, caustic, and silica consumption in the downstream refinery. However, in soybean plants with adequately sized extractors where potential oil yield... 

Does note require phosphoric acid for nonhydratable phosphatide. 

Frankel et al. (1987) stored 800 g of soybean seeds at rewetted moistures of 13, 16, and 20% for 19—50 days at 4l°C. Soybeans at 13 and 16% initial moisture reached 4l-48°C while the 20% moisture soybeans reached 47-49°C. They found free fatty acids (FFA) climbed from 0.20% to about 1.25% for the 13% moisture soybeans in 49 days. For the 16% moisture soybeans, FFA elevated from 0.5% to about 2.0% in about 27 days. For the 20% moisture soybeans, FFA went from 0.6 to 2.3% in about 28 days. Phosphorus in crude oil before degumming from the 13% moisture-stored soybeans dropped from 1044 ppm to about 400 ppm during the 50-day period. For the 16% moisture beans, it dropped faster from 850 ppm to 0 in 27 days and for the 20% moisture beans, it dropped from 500 ppm to 0 in about 20 days. The reduction in phosphorus was explained by formation of nonhydratable phosphatides, which are made up of Ca and Mg salts of phosphatides (Frankel et al., 1987). They also scanned samples from 1100-2500 nm by using a computerized spectrophotometer, and when second derivatives were taken, they found absorption bands at 2260 nm (R = 0.86) and 1810 nm (R = —0.72) that were correlated to FFA. 

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