Batch interesterification

The hpase activity unit (BIU, batch interesterification units) is described in publication AF 206-2 obtainable from Novo Nordisk A/S. 

To measure the activity in acidolysis, triolein was esterified with equimolar amounts of palmitic acid at 60°C by means of immobilized lipase (Fig. 4). The incorporation of palmitic acid into the triolein is measured by GIC of fatty acid methyl esters obtained after methoxylation of the triglycerides (8,9). One Batch Interesterification Unit (BIU) corresponds to 1 /xmol of palmitic acid incorporated (initial activity) into triolein per min. 

The activities in acidolysis of tricaprin with different fatty acids were measured in separate experiments, each performed like the assay for batch interesterification units. It is observed that the enzyme has seme specificity towards saturated fatty acids. This kind of specificity is unique, and has not previously been described. 

Garcia, H.S., Keough, K.J., Arcos, J.A., Hill, C.G.J. 2000. Interesterification (acidolysis) of butterfat with conjugated linoleic acid in a batch reactor. J. Dairy Sci. 83, 371-377. 

There is considerable worldwide interest in the application of lipases for fat modification and ester synthesis. In systems with low water activity, lipases are able to catalyze ester synthesis as well as interesterification reactions in fats. The lipase reactions under low water activity can be performed in several ways. We consider batch or continuous reactions in melted fats by use of immobilized lipases as the most relevant way for the industry. 

Although interesterification will occur in the absence of added catalysts at sufficiently high temperatures, catalysts are employed by industry to speed this reaction, reducing reaction time and the sample degradation that occur at elevated temperatures. The most commonly used inorganic catalysts are alkaline ones such as sodium methoxide, sodium ethoxide, sodium or potassium metal, and alloys of sodium and potassium. Catalyst concentrations of 0.05% to 0.1% are employed. As the catalysts will react with water, free fatty acids, and oxidized compounds, it is important to use clean, dry feedstocks. Reaction temperatures are generally kept below 100°C. The reactions can be mn in batch or continuous formats. In batch mode, the reaction times are typically less than an hour. 

Continuous interesterification processes exist but to date none have been commercialized. Interesterification is generally performed in small batches by specialty processors. An alternate method of increasing interest is directed interesterification using enzymes. The process is generally applied to palm-oil-based materials such as cocoa butter substitutes and to coconut oils. There is some concern about the effectiveness of interesterification with physical refined oils as low levels of FFA must be present or the reaction will not proceed as planned (5). Although not a hazardous process, interesterification is often included in the hydrogenation section of the refinery because of the similarity of the reactors. 

Xu, X., Balchen, S., and Adler-Nissen, J., Pilot batch production of specific-structured lipids by lipase-catalyzed interesterification preliminary study on incorporation and acyl migration, J. Am. Oil Chem. Soc., 75, 301-308, 1998. 

Lipase-catalyzed interesterification of fats and oils can be accomplished either by using a stirred batch reactor or with continuous processing using a fixed-bed reactor. 

An alkaline catalyst, such as sodium methoxide, or metallic sodium is normally used. The fat must be dry and free of fatty acids to prevent destruction of the catalyst. When the reaction is conducted at a temperature that maintains the fat in a molten state the process leads to "random" interesterification. "Directed" interesterification takes place when a portion of the fat is in a solid state. In a typical case of random interesterification the fat is heated in a closed tank under vacuum to 135°-150°C, 0.1% of catalyst is added, and mixed thoroughly for about 0.5 hr. A sample is taken for analysis and if the reaction is not complete an additional amount of catalyst is added and mixed for another 0.5 hr. When the interesterification is complete approximately 0.05% of phosphoric acid is added with agitation to neutralize the catalyst. The batch is then washed or bleached. 

Enzymic interesterification is a recent development of considerable promise. Its advantage over the more conventional procedures lies in the additional control of product composition. The lipase, coated on to a support material (kieselguhr, hydroxylapatite, alumina) in the presence of a little water, supports interesterification at about 40 °C and usually requires 16-70 h for complete reaction but can be shorter depending on catalyst activity. The process may be operated in a batch or continuous manner. The substrate is a natural oil or fat to which may be added a second oil or fat and/or a particular fatty acid or fatty acid mixture. Three types of enzyme are available. One type (from Candida cylindricae, Coryne-bacterium acnes or Staphylococcus aureus) is nonspecific and leads to complete randomization of all acids at all positions. The product is the same as that obtained from the ordinary catalytic process. A second type of lipase (from Aspergillus niger, Mucor favanicus, Rhizopus arrhizus, / . delemar... 

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