Biomedical Engineering Reference
In-Depth Information
TABLE 10.8
Genetic Improvement of Food-Grade Microorganisms
Type of
Fermentation
Microorganism
Nature of Improvement
Implications
Dairy
Cheese
Bacteriophase (virus)
resistance
Eliminate economic losses due to
destruction of culture by viruses
Yogurt
Accelerated ripening
Decreased storage costs
Higher levels of beta-
galactosidase
More digestible product for lactose-
intolerant individuals
Meat
Sausage
Bacillus subtilis
Bacteriocin production
Inhibition of pathogens and
spoilage organisms
Cereal
Beer
Bacillus subtilis
Alpha-amylase production
Production of “lite” or low-calorie
beer
Bread
Bacillus subtilis
Higher levels of maltose
permease and maltase
More consistent and improved
leavening
Adapted from Harlender 90 and Jelen. 125
a much faster pace, and the ability to cross species barriers greatly expands the
available gene pool. Some of the genetic improvements that have been achieved in
microorganisms are shown in Table 10.8 . 90,127 This table shows microorganisms used
to produce fermented dairy, meat, and cereal products. Current research is focused on
the construction of food-grade cloning vectors (multifunctional plasmids derived solely
from the DNA of food-approved organisms), the development of high frequency gene
transfer systems, and the identification and characterization of desirable traits.
Another novel technology currently being used to select foods with longer shelf
life is based on molecular markers. In contrast to morphological characters, the
genetic basis, and thus the expression of molecular characters, is well worked out
and predictable; nonetheless, there are certain complications to using different
classes of molecular markers due to variation in inheritance, recombination, and
linkages. Thus, the expression of molecular characters must be interpreted carefully
in terms of what is known about the genetic basis of the markers used. If employed
correctly, however, these types of markers can provide detailed information regarding
the genealogy of hybrids and thus can be used to verify morphological and chemical
predictions. The advantages of molecular vs. morphological markers for studies of
hybridization have been reviewed by Rieseberg and Wendel 129 and include: (1) the
large number of independent molecular markers available for analysis; (2) the gen-
erally low levels of nonheritable molecular variation; and (3) the apparent selective
neutrality of many molecular markers.
Most studies of hybridization to date have been limited by the numbers of
independent molecular markers differentiating hybridization taxa. This problem is
most severe for the cytoplasmatic genomes and the nuclear ribosomal RNA genes,
 
 
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