BLBS102-c12 BLBS102-Simpson March 21, 2012 13:11 Trim: 276mm X 219mm Printer Name: Yet to Come
12 Pectic Enzymes in Tomatoes 243Table 12.1.First-Order Reaction Rate Constants,k(sec−^1 ), for High Pressure PME and PG Inactivation as a
Function of Processing Temperature (Based on Data Presented by Crelier et al. 2001)First-Order Reaction Rate Constants,k(sec−^1 )PME PGP (MPa) 60 ◦C65◦C70◦C75◦C30◦C40◦C50◦C60◦C0.1 161 · 10 −^6872 · 10 −^66250 · 10 −^63680 · 10 −^6
100 7.58· 10 −^6163 · 10 −^6883 · 10 −^6574 · 10 −^6 52.6· 10 −^6
300 9.70· 10 −^6112 · 10 −^6 51.4· 10 −^6 18.3· 10 −^6309 · 10 −^6
400 38.6· 10 −^6193 · 10 −^6351 · 10 −^6701 · 10 −^62510 · 10 −^6
500 103 · 10 −^63890 · 10 −^64090 · 10 −^63620 · 10 −^67020 · 10 −^6
600 43.8· 10 −^6 44.3· 10 −^6 70.2· 10 −^6 52.5· 10 −^61720 · 10 −^64810 · 10 −^67530 · 10 −^6
800 1500 · 10 −^62330 · 10 −^62920 · 10 −^62710 · 10 −^6of the one or the other enzyme by appropriately optimizing the
processing conditions (pressure, temperature, and time).FUTURE PERSPECTIVES
Texture in ripe tomato fruit is largely dictated by cell wall disas-
sembly during the ripening process. Cell wall polysaccharides
are depolymerized, and their composition is changed as ripening
progresses. The coordinated and synergistic activities of many
proteins are responsible for fruit softening, and although
expansins and PGs are among the more abundantly expressed
proteins in ripening tomato fruit, the modification of their
expression has not been sufficient to account for all of the cell
wall changes associated with softening or for the overall extent
of fruit softening. The texture of fresh fruit directly influences
the rheological characteristics of processed tomato products.
Viscosity is influenced by modifications of the cell wall architec-
ture but also by changes that may affect polysaccharide mobility
and interactions of different components in juices and pastes.
Since cell wall metabolism in ripening fruit is a complex process
and many enzymes have been identified, which contribute to
this process, further insight to the effect of these enzymes on
fruit texture and processing attributes can be gained by the
simultaneous suppression or over-expression of combinations
of enzymes. Of course, the quest is on for identification of
enzymes acting on RGI, RGII, and XGA of plant pectins similar
to those found in fungi and bacteria (Wong 2008). Moreover,
as our knowledge on cell wall biosynthesis and deconstruction
increases, the ability to genetically engineer pectin structure in
target plants would further improve fruit texture and processing
characteristics (Ramakrishna et al. 2003, Vicente et al. 2007,
Matas et al. 2009). Manipulation of the expression of multiple
ripening-associated genes and/or transcription factors that reg-
ulate ripening (Vrebalov et al. 2009) in transgenic tomato lines
will further shed light to the ripening physiology, postharvest
shelf life and processing qualities of tomato fruit. Finally, the
interest exists and efforts are made to design optimal processes
for selective enzyme inactivation and thus for productionof products with desirable characteristics, by introducing
pressure as an additional (to time and temperature) processing
variable.ACKNOWLEDGMENTS
The authors would like to thank Asst. Professor P. Chris-
takopoulos, National Technical University of Athens, School of
Chemical Engineering, Biosystems Technology Laboratory, and
Dr. C. Mallidis, Institute of Technology of Agricultural Prod-
ucts, National Agricultural Research Foundation of Greece, for
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