Food Lipids: Chemistry, Nutrition, and Biotechnology

leukotrienes (hydroxy fatty acids and lipoxins), which are synthesized via lipoxygenase,
as illustrated in Figure 4.
A proper balance of n-3 and n-6 fatty acids should be maintained in the diet
and SL products. High concentrations of dietary 18:2n-6 may lead to increased production
of immunosuppressive eicosanoids of the 2- and 4-series [prostaglandin E 2
(PGE 2), thromboxane A 2 (TXA 2), leukotriene B 4 (LTB 4)]. However, diets high in
20:5n-3 will inhibit eicosanoid production and reduce inflammation by increasing
production of TXA 3, prostacyclin (PGI 3), and LTB 5. Diets including n-3 PUFAs also
increase HDL-chol and interleukin-2 (IL-2) levels. On the other hand, they inhibit
or decrease the levels of IL-1, LDL-chol, and very low density lipoprotein cholesterol
(VLDL-chol).
5. Omega-9 Fatty Acids
The n-9 fatty acids or monounsaturates are found in vegetable oils such as canola,
olive, peanut, and high-oleic sunflower as oleic acid (18:n-9). Oleic acid can be
synthesized by the human body and is not considered an essential fatty acid. However,
it plays a moderate role in reducing plasma cholesterol in the body (26). Oleic
acid is useful in structured lipids for fulfilling the long chain triacylglycerol requirements
of SLs as given in Table 1.
6. Long Chain Saturated Fatty Acids
Generally, saturated fatty acids are believed to increase plasma and serum cholesterol
levels, but it has been claimed that fatty acids with chains 4–10 carbon atoms long
do not raise cholesterol levels (37,38). Stearic acid has also been reported not to
raise plasma cholesterol levels (39). TAGs containing high amounts of long chain
saturated fatty acids, particularly stearic acid (18:0), are poorly absorbed in man
partly because 18:0 has a melting point higher than body temperature; they exhibit
poor emulsion formation and poor micellar solubilization (40). The poor absorption
of saturated long chain triacylglycerols (40) makes them potential substrates for lowcalorie
SL synthesis. Indeed, Nabisco Foods Group used this property of stearic acid
to make the group of low-calorie SLs called Salatrim (now Benefat) (see Sec. II.B.2),
which consist of short chain aliphatic fatty acids and long chain saturated fatty acids,
predominantly C18:0 (41). Caprenin, an SL produced by Procter & Gamble, contains
C22:0, which is also poorly absorbed. An SL containing two behenic acids and one
oleic acid has been used in the food industry to prevent chocolate bloom and to
enhance fine crystal formation of palm oil and lard products (42).
B. Synthesis of Structured Lipids
1. Chemical Synthesis
Chemical synthesis of SLs usually involves hydrolysis of a mixture of MCTs and
LCTs and then reesterification after random mixing of the MCFAs and LCFAs has
occurred, by a process called transesterification (ester interchange). The reaction is
catalyzed by alkali metals or alkali metal alkylates. This process requires high temperature
and anhydrous conditions. Chemical transesterification results in desired
randomized TAG molecular species, known as SLs, and in a number of unwanted
products, which can be difficult to remove. The SL product consists of one (MLL,
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.