Food Lipids: Chemistry, Nutrition, and Biotechnology

available (cf. Sec. V.C.4 and Ref. 183). Any of these genetic strategies would augment
the more conventional (and reactionary!) approach of preparing cocoa butter
substitutes from various lipid sources via postproduction enzymic modification using
lipases (see Chapters 26 and 27). Second, from a mechanistic viewpoint, understanding
the influence of temperature on triacylglycerol assembly in cocoa beans may
allow for identification of a means to ameliorate the problem of ‘‘soft’’ cocoa butters
that originate in warmer climates (223).
With regard to other biotechnological approaches to producing cocoa butter,
plant cell (suspension) cultures have been investigated for this purpose (224). Unfortunately,
nondifferentiated cells produce lipids that resemble functional (and not
storage) lipids in fatty acyl composition. This can be easily explained in terms of
developmental and organ-specific regulation of storage lipid accumulation. Tissue
differentiation during culture was previously shown to be important in that maturing
cacao embryos grown in vitro did accumulate limited amounts of triacylglycerol with
a molecular species profile resembling that of cocoa butter (225).
A lot of interest has been devoted to preparing and testing transgenic plants
that produce 12:0-rich oils, specifically in canola (215,226). Such oils would serve
as replacements for selected tropical oils (viz., coconut, palm kernel) and could be
used in applications such as cocoa butter extenders, coatings, simulated dairy products,
bakery goods, and spreads. The apparent excitement about the development of
a canola strain that produces lauric acid is somewhat perplexing, considering the
campaign of ‘‘tropical-oil bashing’’ (also including palm oil) in North America that
was initiated in the late 1980s (227,228). Based on the contribution of tropical oils
to the diet of the U.S. public, the slight hypercholesterolemic effect of 12:0 (22�) is
probably dismissible (230), and in the case of palm oil, not at all relevant (231)
(because palm oil essentially lacks 12:0). However, the negative image of 12:0-rich
oils is still apparent, since the need to address this issue with 12:0-producing transgenic
canola was met with a comment suggesting that the canola transformant stores
12:0 in a ‘‘novel form’’ (2320. This speculation was apparently based on the difference
in LPATT activities of rapeseed and coconut, in that the former excludes, while
the latter permits, the positioning of 12:0 at the sn-2 site (see Secs. V.D.2 and V.E.2,
Table 6, and Ref. 233). It remains to be determined whether this subtle difference
in positional distribution has any impact on the nutritional or health effects of 12:0
from the two sources. In any case, the suitability of transgenic plants for producing
other medium chain fatty acids (8:0 and 10:0) is also being explored (234).
Finally, opportunities exist to use transgenic plants to produce waxes that may
be designed to function as moisture barriers in foods. Potential industrial uses of
waxes as lubricants and cosmetics will likely provide the impetus for developments
in this area (148,212). However, an improved understanding of structure–function
relationships between molecular characteristics of waxes and component migration
in foods will place food scientists in a position to also benefit from wax production
by transgenic plants.
C. Modifying Chemical Functionality
Genetic manipulation of lipid biosynthesis has already expanded to potential applications
beyond the scope of storage lipids (triacylglycerols). The overexpression of
�9DES in transgenic tomato (Lycopersicum esculentum) fruits results in increases
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.