Biomedical Engineering Reference
In-Depth Information
sweet-tasting protein called monellin. The gene comes from a tropical shrub, and
opens up the prospect for low-calorie, sweet-tasting vegetables. 10 Also researchers
at the Institute of Genetics in Berlin have inserted an antisense gene that blocks the
production of ADP-glucose pyrophosphorylase, an enzyme which converts sucrose
into starch in tubers; sucrose just piles up instead of being converted into starch. 10
A wild tomato from the Galapagos islands ( Lycopersiconchessmanii ) has been
selected because it has 40 times more vitamin A than regular commercial tomatoes.
The Galapagos tomatoes also contain an average of 58 mg per gram of beta-carotene,
compared with approximately 1.5 mg per gram found in the common tomato. 17 The
USDA has crossed the Galapagos tomatoes with Floradade, a commercially culti-
vated tomato grown for fresh market uses. The result has been orange tomatoes with
about 30 mg of beta carotene per gram. The new hybrid also has a tomato taste
reminiscent of Floradade. With consumers becoming more and more health-con-
scious, foods containing vitamin-packed tomatoes may be demanded from food
processors in the future. 17
Improving Shelf Life
When variation is limited or when plant breeders are forced to use unadapted
germplasm, traditional plant breeding requires many generations and considerable
effort to produce elite lines with the desired phenotype. Creating a large mutagenized
population and screening the resultant plants for reduced expression is time-intensive
and potentially costly. Plants selected also may need extensive backcrossing to
remove random mutations not associated with the trait of interest. In addition, a trait
may have a negative commercial value when expressed in seed, but may be required
by roots or leaves for optimum growth and development.
The advent of recombinant DNA technology has given plant breeders new tools
in their quest to improve agronomically important crops. One of the uses of the
recombinant DNA technology is the production of new lines of oilseeds with less
polyunsaturated fatty acids which increases shelf life. 53,54 Figure 10.3 shows gener-
ated changes in the fatty acids of genetically engineered sunflower and soybean as
compared to regular crops. 53 The improved oxidative stability over regular soybean
oil can be translated into longer shelf life and longer fry life. Considering that
soybean oil made up 75% of total U.S. consumption of edible fats and oils in 1992,
this is a significant development. 53 The susceptibility to oxidation of polyunsaturated
fatty acids is greater than that of monounsaturated and saturated fatty acids. In an
attempt to increase the oxidative stability of oils for use in high-temperature appli-
cations, while maintaining the cholesterol-lowering properties, recombinant DNA
technology has been used in soybean and canola oils. 54 Saturated fatty acid levels
remained the same (Figure 10.3). 53 The presence of linolenic acid in soybean oil has
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