Biomedical Engineering Reference
In-Depth Information
engineered to ripen on the vine longer and so be tastier than currently available fresh
produce. 30,31 The Flavr Savr is the first genetically engineered whole food to receive
premarket scrutiny from the FDA, which ordinarily evaluates food additives rather
than whole foods. Calgene used resistance to the antibiotic, kanamycin, as a marker
while selecting modified plant cells during the early stages of engineering the Flavr
Savr tomato. The kanamycin-resistance gene (kan-r), though, plays no further role
in the intact, engineered plant or in its tomatoes. 30,32-34 The business end of the two-
part gene construct in the Flavr Savr tomato is an antisense gene targeting the gene
encoding PG, an enzyme produced in ripening tomatoes. Since this antigene blocks
production of PG, it prevents PG's catalytic activity. When active, PG helps to
dissolve pectin, a polysaccharide that imparts firmness to tomatoes. Because the
antisense gene halts PG production, Flavr Savr tomatoes remain firm instead of
becoming soft, as they ripen. Since ordinary tomatoes produce plenty of PG, they
are picked when still hard and long before they ripen naturally. In this hardened,
but not so tasty state, ordinary tomatoes survive better transport and handling on the
way to distant markets. By contrast, because the Flavr Savr tomato lacks PG and
softens much less readily, it can stay on the vine until ripe and flavorful and still
survive transport and handling. According to Calgene, the Flavr Savr is not so tasty
as tomatoes produced by traditional farmers but is far more tasty than tomatoes
currently available in most U.S. supermarkets. 18,30 The consensus view is that use
of antisense gene to block PG production poses no conceivable risk to consumers.
And although speculative concerns were raised regarding the kan-r gene's potential
for spreading antibiotic resistance, which is a public health problem, FDA officials
have not argued that putting the kan-r gene in the Flavr Savr poses a significant risk.
Moreover, traditional toxicology experiments in which rats were administered high
doses of Flavr Savr also indicated that the tomato is safe. 30,31,34 To allow the pro-
cessing industries to benefit from these genetic improvements, field trials have been
carried out with tomato hybrids whose viscosity parameters have been improved
through the introduction of PG effect genes. It is anticipated that commercial prod-
ucts resulting from this work will most likely reach the market. 35,36 The full range
of benefits of enhanced-viscosity tomatoes to the processing company lies in cost
savings from increased product yield. However, a much broader range of benefits
will be realized by the grower, the consumer, and the environment ( Table 10.4 ). 36
A number of investigators 37,38 have examined the effects of storage temperature
on fruit and vegetable quality, especially chill damage. These studies have centered
mainly on gross changes. Other studies 39,40 have focused on changes in volatile
composition during ripening. 41 Another study 42 has been comprehensive in correlat-
ing various parameters of tomato flavor. There are also reports of some of the
methodology used in the data gathering and analysis of tomato volatiles. 43 Changes
in the most important volatile and non-volatile compounds have been quantified
along with physical properties and attempts have been made to correlate these flavor
chacteristics with each other and with treatments under conditions that closely
simulate current commercial practices of storage and ripening. 44 Although more than
400 compounds have been identified as volatile constituents of tomatoes and tomato
products, 45 only a limited number are essential to tomato flavor. Stern et al. 44 found
that the generation of volatiles decreases significantly with storage and ripening
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