Biomedical Engineering Reference
In-Depth Information
fats with the best properties have a high ratio of palmitic to stearic acid. During
hydrogenation, the unsaturated fats are changed by the addition of hydrogen to the
triple and double bonds of the oil. This results in the trans -isomerization of the fat,
which causes the formation of trans fatty acids. The trans fatty acids do not normally
occur in nature and have been shown in some studies to increase the body's level
of serum cholesterol. 53 Selective hybridization of oil seeds can produce a high stearic
acid hybrid oil that would reduce the need to hydrogenate for some solid fat appli-
cations. By using oil produced from selective hybridization, the problem of trans -
isomerization would be eliminated and the labeling of “hydrogenated” avoided.
T RANSGENIC L EGUMES
Quality of Seed Storage Proteins
After cereals, legume seeds are the most important source of food protein at the
world level, and consequently are of remarkable nutritional and economic signifi-
cance. The Leguminosae is an immense botanical family, whose seeds exhibit wide
variations in protein content and quality. Seeds of wild and cultivated crops display
a range of 12 to 55% protein; up to 80% of these proteins can be represented by
storage proteins, reflecting their central role in seed viability. The remaining seed
proteins, over 1000 different types, are involved in metabolic processes, cell struc-
ture, and antinutritional properties, e.g., lectins and protease inhibitors. 58
Legume seed storage proteins are commonly referred to as globulins because
they are salt-soluble at neutral pH. Seed globulins can be mostly divided, for sim-
plicity, into two distinct classes termed 7S and 11S on the basis of their sedimentation
coefficients. The ability to improve the quality of these food proteins would be of
enormous benefit to the agriculture sector, the food industry, and finally the con-
sumer. From a nutritional viewpoint, target areas are: increase of digestibility,
removal of intolerance factors, inducing higher levels of methionine and tryptophan,
much better palatability, and decrease of nutrient binding to improve bioavailability.
From a functional perspective the main objectives are: increase of foaming and
emulsifying properties, increase of solubility at or near the proteins' isoelectric point,
better gelling and texturizing capabilities, lower heat stability, and higher fla-
vor/water/fat binding. 59 An approach for improvement would be to “engineer” the
proteins at the crop level. By defining the ideal combination and composition of
seed globulins, enhancement in quality can be achieved. Recent advances in molec-
ular technology offer a possible solution to the above-mentioned traits. It is now
clear that the production of recombinant seed globulins in bioreactors will never
compete economically with the existing low cost bulk production of protein con-
centrates and isolates. Thus, the generation of transgenic legumes with improved
seed globulins should be considered; it could be achieved by introducing either
totally foreign genes (e.g., globulins from other species) or modified endogenous
globulin genes. The major obstacles to engineering legume seed globulins are related
to the transformation and regeneration procedures of legumes species. Fortunately,
some legumes have now proved to be more amenable to Agrobacterium and biobal-
istic transformations and subsequent regeneration. 59,60
 
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