Thermal Food Processing

528 Thermal Food Processing: New Technologies and Quality Issues
17.6.2 Death Behaviors of B. subtilis Spores ....................................548
17.6.3 Death Behaviors of B. coagulans Spores................................551
17.6.4 Death Behaviors of B. stearothermophilus Spores .................554
17.6.5 Death Behaviors of C. sporogenes Spores..............................555
17.7 Pressure Combined with Mild Heating ................................................558
17.7.1 Shucking of Oyster by Pressure ..............................................558
17.7.2 Autolysis under Pressure and Mild Heating ...........................559
17.7.2.1 Inhibition of Microorganism
Growth by Pressurization ........................................560
17.2.2.2 Autolytic Condition under Pressure........................560
17.2.2.3 Quality of Pressure Autolytic Extract.....................561
17.8 Conclusions ...........................................................................................562
Acknowledgments .............................................................................................562
References .........................................................................................................563
17.1 INTRODUCTION
Many foodstuffs have been treated through various types of thermal processings,
such as boiling, steaming, baking, and frying. By such treatments the foodstuffs
are remade into foods and dishes with favorable tastes, and with nutritive
function to ease digestion, as well as extending the shelf life and safety. Changes
in such functions depend on the relationship between temperature and time.
When pressure is added as another factor to the relationship, it is largely
unknown whether the functions will change favorably or unfavorably, or will
not change at all. To clarify these matters, the authors investigated kinetically
such changes and the effects of sterilization through thermal treatment combined
with pressure. 1–6 Furthermore, the combination of high hydrostatic pressure
(HHP) and mild heating has also been tested as an innovative and practical
technique for food processing. 7
Nearly a century ago, Hite, 8 for the first time, started investigating HHP for
pasteurizing milk. Since then, a lot of studies related to HHP, such as the sterilization
of microorganisms by HHP, 9–13 enzyme reaction under pressure, 14 and the softening
of muscle by HHP, 15,16 have been reported. Furthermore, the number of studies of
HHP have greatly increased in Japan since the end of the 1980s, 17 and also in the
U.S. and Europe. Although HHP treatment had been first investigated as a sterilization
procedure without heating, it has also been noticed as a new food processing
technique. Some innovative techniques using pressure were recently practiced in the
food industry, for instance, shucking of oyster by pressure, 18–20 production of guacamole
by pressure in the U.S., production of rice cakes by pressure, 21 and an
autolytic technique of unsalted fish protein under pressure. 7
Although there are many studies on the effects of HHP on sterilization, 22 few
studies on thermal treatment combined with pressure have been reported. 23 This is
because it is difficult to use HHP at high temperatures, in particular higher than
100°C, and also to keep the pressure during the thermal treatment. The aim of this
chapter is to use our data to illustrate the process of pressure-assisted thermal