Chemical interesterification is one of the major modification techniques and basically involves a random rearrangement of the sn-1, sn-2, and sn-3 fatty acids over the triglycerides present in the mixture (Fig. 1). A similar result can be obtained when using a random lipase such as that from Candida rugosa* (38, 67), Pseudomonas fluorescens (68), or Pseudomonas cepacia (69). Using a 1,3-specific lipase, only the fatty acids on the outer positions of the triglyceride molecules will be randomized. In this case the sn-2 position remains intact, which implies that a different triglyceride mixture will result, as compared to the random process.
In both cases the rearrangement process can be regarded as a statistical process, and hence the final, equilibrium composition of the product can be easily calculated. For example, assuming only three fatty acids—X, Y, and Z—present in a TAG mixture, the molar concentration of an individual types of triglycerides follows from:
X3 = x • x • x 1,3-specific process: XYZ = 2^ x1;3 • y2 • z1;3
XYX = xu • y2 • xu in which x, y, z = the molar fractions of X, Y and Z in overall fatty acid composition of the trigylceride mixture; 6, 3, 1 = the number of ways in which three, two, and one type of fatty acids, respectively, can be distributed over the sn-1, sn-2, and sn-3 positions; x1,3, z1,3 = the molar fractions of X and Z on the sn-1 and sn-3 positions; y2 = the molar fraction of fatty
* Candida rugosa, formerly referred to as Candida cylindracea.
acid Y on the 2-positions; and 1, 2 = the number of ways the two and one type of fatty acids, respectively, can be distributed over the sn-1 and sn-3 positions in the triglyceride mixture.
The overall- and 2-position fatty acid composition in a triglyceride mixture can be obtained by conventional HPLC or GC analysis. The 1,3-position composition then follows by calculation. Though the above presented rules specifically refer to interesteri-fication of triglycerides, they also apply to acid-olysis—i.e., the reaction between triglycerides and fatty acids or single fatty acid esters. However, in this case the overall 1,3-positional fatty acid composition follows from the 1,3-positional fatty acid composition in the triglyceride fraction, the free fatty acid composition, and the molar ratio of free fatty acids to triglycerides.
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