Front Matter

of TAG species can then be calculated from the peak areas. The TAG fraction of the

original SCO and acidolyzed oil were analyzed by HTGC (an example is shown in

Figure 4) (Iwasaki et al., 1999). The peaks were identified by comparing their re-

tention times to those of authentic TAGs.

9.2.7 TLC/FID

Although thin-layer chromatography/flame ionization detector (TLC/FID) (IatroS-

canÒ) is a very convenient analytical instrument, its application to the monitoring of

the time course of the synthesis of sTAG containing PUFA is limited to the detection

of the decrease in the pure substrate contents of the reaction mixture and the for-

mation of partial acylglycerols (byproducts). However, separation within a class

of partial acylglycerols or TAGs is not possible.

9.3 Increasing the yield

As is the case with most enzymatic reactions, the performance of enzymatic synth-

esis of pure sTAG containing PUFA depends on many factors involving type of

reaction, enzyme and its immobilization, temperature, water content, composition

of substrates, physical properties of the substrates, reaction time, mode of opera-

tion, etc. Some of these factors are briefly mentioned in the following text, together

with examples of reactions yielding pure AAB- and ABA-types of sTAG, both of

which contain PUFA.

9.3.1 Choice of enzyme and its immobilization

Enzymes involved in sTAG synthesis are exclusively lipases. Careful exploitation of

positional (regional) specificity, FA specificity and stereospecificity of lipases can

provide a maximum yield of the desired sTAG. To date, most researchers have uti-

lized fungal lipases such as those fromRhizomucor miehei, Rhizopus delemar, Rhi-

zopus javanicus, andRhizopus niveus, which are 1,3-specific and hence are effective

to synthesize ABA type sTAG. As for non-regiospecific lipases, a number of micro-

bial lipases are commercially available such as those fromCandidasp. (C. antarctica

andC. rugosa) and those fromPseudomonassp. (Ps. fragi, Ps. cepacia, Ps. glumae

andPs. fluorescens). Some lipases also exhibit stereospecificity, e.g.Rhizomucor

mieheiand Carica papayalatex lipases have been claimed to showsn-1 and

sn-3 preferences, respectively, in interesterification reactions (Villeneuve et al.,

1997; Chandler et al., 1998), although they are not absolute. There is a potential

that, in future, it may be possible to synthesize a chiral sTAG by using such a stereo-

specific lipase.

9.3 Increasing the yield 159