Food Lipids: Chemistry, Nutrition, and Biotechnology

functions and are thus often referred to as structural lipids. Both structural lipids and
seed triacylglycerols contain glycerol-bound fatty acids, and thus it is not surprising
that their respective synthesis pathways share many common steps. Re-engineering
triacylglycerol biosynthesis must not compromise the synthesis of the structural lipids
necessary to support growth and viability.
If some desirable lipid compositions are indeed incompatible with viable seed,
there may be a unique opportunity in engineering such oil types into either oil palm
or avocado mesocarp tissues. These are oil-rich tissues whose natural fate is to rot
away after fruit dehiscence. Since plant progeny do not directly depend on the viability
of these tissues, they might be engineered to ‘‘self-destruct’’ by making, for
example, very solid fats rich in long chain saturated fatty acids. Engineered oil palm
fruits could be harvested by standard means and the palm kernels (the oil palm seed)
would be normal—assuming that the technology employed worked to ensure that
the changed fatty acid composition was limited to just the mesocarp.
Another type of limitation that is of commercial interest is the ultimate amount
of oil obtainable from a crop. While focused on traits like disease resistance and
plant stature, much of the oilseed crop breeding community measures success by
how much seed is harvested per acre. As crop yields go up, one expects the cost of
food oils to come down. At a different level, breeders and genetic engineers alike
are interested in increasing the oil content on a per-seed basis. Soybeans typically
contain only 20–25% oil by weight, whereas canola seed is typically 40–45%. Peanuts
can be 50% oil, while the cacao bean is 60% cocoa butter. It seems physiologically
possible, therefore, to increase the seed oil content in soybean and canola with
correspondingly dramatic effects on the cost of producing vegetable oils from these
major crops.
B. Practical Limitations
Even though the scope of possible lipids modification projects must be very widely
based on the natural variation in seed lipids found among plants form around the
world, there are factors, other than natural ones, that practically limit what will be
done in the near term.
Genetic engineering of crop plants requires a battery of expertises: plant physiology,
enzymology, molecular biology, gene transfer cell biology, prototype evaluation,
and plant breeding. Much of an engineering project entails sequential applications
of each area of expertise to the eventual goal. Coupled to the obvious costs
of having these expertises in place and having the time needed to go from concept
to practice is a consideration of the technical risk entailed when one is embarking
on a new project. Financial modeling and analyses of the eventual value and return
versus development costs and risk may argue against ever starting certain projects.
Part of the eventual value may hinge on the production system that allows the
value to be ensured and protected. Since genetically engineered genes behave like
other genes once present in a plant, they are necessarily transmitted by pollen. Vegetable
oils are often zygotic characters. That is, the chemical composition is determined
by both parents. Thus if a transgenic canola crop is grown immediately adjacent
to normal canola, an interchange of pollen will decrease the purity of both
crops. So, novel oilseed crops may have to be grown in carefully managed districts.
Of course, there are some precedents for producing ‘‘specialty’’ oils, including the
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