Dynamic model for predicting survival of mature larvae of Tribolium confusum during facility heat treatments

Structural heat treatment, a viable alternative to methyl bromide fumigation, involves raising the ambient temperature of food-processing facilities between 50 and 60 degrees C by using gas, electric, or steam heaters, and holding these elevated temperatures for 24 h or longer to kill stored-product insects. A dynamic model was developed to predict survival of mature larvae, which is the most heat-tolerant stage of the confused flour beetle, Tribolium confusum (Jacquelin du Val), at elevated temperatures between 46 and 60 degrees C. The model is based on two nonlinear relationships: 1) logarithmic survival of T. confusum mature larvae as a function of time, and 2) logarithmic reduction in larval survival as a function of temperature. The dynamic model was validated with nine independent data sets collected during actual facility heat treatments conducted on two separate occasions at the Kansas State University pilot flour and feed mills. The rate of increase of temperature over time varied among the nine locations where mature larvae of T. confusum were exposed, and the approximate heating rates during the entire heat treatment ranged from 1.1 to 13.2 degrees C/h. The absolute deviation in the predicted number of larvae surviving the heat treatment was within 3-7% of the actual observed data. Comparison of the absolute deviation in the time taken for equivalent larval survival showed that the model predictions were within 2-6% of the observed data. The dynamic model can be used to predict survival of mature larvae of T. confusum during heat treatments of food-processing facilities based on time-dependent temperature profiles obtained at any given location.     

Evaluation of thiamethoxam and imidacloprid as seed treatments to control European corn borer and Indianmeal moth (Lepidoptera: Pyralidae) larvae

Efficacy of thiamethoxam (Cruiser) and imidacloprid (Gaucho) were evaluated as seed treatments for controlling European corn borer, Ostrinia nubilalis (Hübner) and Indianmeal moth, Plodia interpunctella (Hübner) larvae in stored grain. At approximately 22-26 degrees C, all fifth instar European corn borers died after two or 4 d of exposure to corn treated with 250 and 500 ppm thiamethoxam, respectively, while mortality of larvae exposed for two and 4 d on corn treated with 6.3-937.5 ppm imidacloprid did not exceed 48% at any concentration. At 29 degrees C, all nondiapausing fifth instars were killed after 3, 4, and 6-d exposure to 400, 300 and 200-ppm thiamethoxam, respectively, while survival increased at successively lower concentrations of 100, 50, 25, and 12.5 ppm. At 29 degrees C, the LC50 decreased from 85.9 to 7.2 ppm as the duration of exposure on treated corn increased from 2 to 6 d. All second and third instar Indianmeal moth larvae died after a 5 d exposure period to corn grain treated with thiamethoxam at 50 ppm or higher, but as the larvae aged, higher concentrations and longer exposure periods were required to give 100% mortality of each larval instar. Similar results were obtained when larval Indianmeal moths were exposed on corn treated with imidacloprid, or on sorghum treated with thiamethoxam. Mature wandering phase fifth instars were the most tolerant larval stage of the Indianmeal moth.     

Thermal death kinetics of red flour beetle (Coleoptera: Tenebrionidae)

While developing radio frequency heat treatments for dried fruits and nuts, we used a heating block system developed by Washington State University to identify the most heat-tolerant life stage of red flour beetle, Tribolium castaneum (Herbst), and to determine its thermal death kinetics. Using a heating rate of 15 degrees C/min to approximate the rapid heating of radio frequency treatments, the relative heat tolerance of red flour beetle stages was found to be older larvae > pupae and adults > eggs and younger larvae. Lethal exposure times for temperatures of 48, 50, and 52 degrees C for the most heat-tolerant larval stage were estimated using a 0.5th order kinetic model. Exposures needed for 95% mortality at 48 degrees C were too long to be practical (67 min), but increasing treatment temperatures to 50 and 52 degrees C resulted in more useful exposure times of 8 and 1.3 min, respectively. Red flour beetle was more sensitive to changes in treatment temperature than previously studied moth species, resulting in red flour beetle being the most heat-tolerant species at 48 degrees C, but navel orangeworm, Amyelois transitella (Walker), being most heat tolerant at 50 and 52 degrees C. Consequently, efficacious treatments for navel orangeworm at 50-52 degrees C also would control red flour beetle.     

Susceptibility of Plodia interpunctella (Lepidoptera: Pyralidae) developmental stages to high temperatures used during structural heat treatments

Heating the ambient air of a whole, or a portion of a food-processing facility to 50 to 60 degrees C and maintaining these elevated temperatures for 24 to 36 h, is an old technology, referred to as heat treatment. There is renewed interest in adopting heat treatments around the world as a viable insect control alternative to fumigation with methyl bromide. There is limited published information on responses of the Indian meal moth, Plodia interpunctella (Hübner), exposed to elevated temperatures typically used during heat treatments. Time-mortality relationships were determined for eggs, fifth-instars (wandering-phase larvae), pupae, and adults of P. interpunctella exposed to five constant temperatures between 44 and 52 degrees C. Mortality of each stage increased with increasing temperature and exposure time. In general, fifth-instars were the most heat-tolerant stage at all temperatures tested. Exposure for a minimum of 34 min at 50 degrees C was required to kill 99% of the fifth-instars. It is proposed that heat treatments aimed at controlling fifth-instars should be able to control all other stages of P. interpunctella.     

Exposure to pretreatment hypothermia as a determinant of heat killing

When Chinese hamster ovary (CHO) cells were exposed to 22 degrees C for 2 hr prior to 42.4 degrees C hyperthermia, neither the shoulder region of the survival curve nor the characteristic development of thermotolerance after 3-4 hr of heating were observed. Absolute cell survival after 4 hr at 42.4 degrees C was decreased by a factor of between 10 and 100 (depending on the rate of heating of nonprecooled controls). Conditioning at 30 degrees C for 2 hr, 26 degrees C for 2 hr, or 22 degrees C for 20 min followed by heating to 42.4 degrees C over 30 min did not result in sensitization. Prolonged (16 hr) conditioning at 30 degrees C, however, increased the cytotoxicity of immediate exposure to 41.4 or 45 degrees C with maximum sensitization to 45 degrees C occurring after 6 hr at 30 degrees C. Both 3- and 18-hr pretreatments at 30 degrees C similarly increased the cytotoxicity of 45-41.5 degrees C step-down heating (D0 = 28 min in precooled versus 40 min in nonprecooled cells).     

The potential of the fungus, Muscodor albus, as a microbial control agent of potato tuber moth (Lepidoptera: Gelechiidae) in stored potatoes

Potato tuber moth (PTM), Phthorimaea operculella, is a serious pest of stored potato in most countries where potatoes are grown. Entomopathogens offer promise as alternatives to broad spectrum insecticides for management of this pest. The fungus Muscodor albus, which produces a mixture of antimicrobial volatile organic chemicals, was tested for its insecticidal activity against PTM. Adults and neonate larvae were exposed to volatiles generated by 15 or 30 g of M. albus rye grain culture plus water for 72 h in hermetically sealed 28.3 L chambers at 24 degrees C. Mean percent mortalities in adult moths exposed to 0, 15, and 30 g of fungal formulation were 0.9, 84.6, and 90.6%, respectively. Development to the pupal stage of PTM that were exposed as neonate larvae to 15 or 30 of M. albus culture was reduced by 61.8 and 72.8%, respectively, relative to controls.     

Thermal responses of oriental fruit fly (Diptera: Tephritidae) late third instars: mortality, puparial morphology, and adult emergence

Responses of late third instars of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), to high temperatures (43, 46, and 48 degrees C) were investigated. The different heat exposures not only affected the timing of death but also induced different quantities of malformed puparia and changed the average eclosion time. A majority of larvae died immediately (as larvae) after 30 min at 46 degrees C and > or =15 min at 48 degrees C, whereas most individuals died as pupae after 10-25 min of 46 degrees C, 5-10 min of 48 degrees C, and 40-60 min of 43 degrees C treatments. Lethal times estimated by immediate mortality were longer than those estimated by delayed mortality at the same high temperature. Surviving larvae formed four types of puparial morphology (normal, bottlenose, larviform, and peanut form). The percentage of normal puparia showed a negative correlation with exposure time at all test temperatures. The number of bottlenose was more than the larviform and the peanut at 46 degrees C for < or =20 min and at 48 degrees C for < or =10 min, respectively, whereas the number of larviform was more than the bottlenose and the peanut at 46 degrees C and 48 degrees C for longer exposure times. The average eclosion time increased at first, then decreased as the exposure time prolonged, and the longest average eclosion time occurred in the 40-min exposure at 43 degrees C, 15-min exposure at 46 degrees C, and 10-min exposure at 48 degrees C.     

The dynamics of the induction and regression of puffs 87A, 87C and 93D in the polytene chromosomes of Drosophila melanogaster under the action of anoxia and high temperature]

A study was made of the heat shock puff activity in salivary glands of Drosophila melanogaster larvae after 5 and 20 min treatments with anoxia (dipping into physiological solution), heat shock (37 degrees C), and simultaneously with both the agents. The simultaneous treatment with heat shock and anoxia, as well as treatment with anoxia only blocked the induction of heat shock puffs. They appeared 10-15 min after the treatment during recovery under aerobic conditions. There was a super-additive effect of the simultaneous treatment on the heat shock puffing duration. A specific regulation of the 93D locus was observed. The 93D puff was induced by a 5 min simultaneous treatment with anoxia and heat shock and, as a rule, was not induced by the analogous 20 min treatment. The role of anoxia in blocking heat shock puff induction under simultaneous effects of heat shock and anoxia is discussed.     

Oxygen consumption and body temperature of active and resting honeybees

We measured the energy turnover (oxygen consumption) of honeybees (Apis mellifera carnica), which were free to move within Warburg vessels. Oxygen consumption of active bees varied widely depending on ambient temperature and level of activity, but did not differ between foragers (>18 d) and middle-aged hive bees (7-10 d). In highly active bees, which were in an endothermic state ready for flight, it decreased almost linearly, from a maximum of 131.4 microl O(2) min(-1) at 15 degrees C ambient temperature to 81.1 microl min(-1) at 25 degrees C, and reached a minimum of 29.9 microl min(-1) at 40 degrees C. In bees with low activity, it decreased from 89.3 microl O(2) min(-1) at 15 degrees C to 47.9 microl min(-1) at 25 degrees C and 14.7 microl min(-1) at 40 degrees C. Thermographic measurements of body temperature showed that with increasing activity, the bees invested more energy to regulate the thorax temperature at increasingly higher levels (38.8-41.2 degrees C in highly active bees) and were more accurate. Resting metabolism was determined in young bees of 1-7 h age, which are not yet capable of endothermic heat production with their flight muscles. Their energy turnover increased from 0.21 microl O(2) min(-1) at 10 degrees C to 0.38 microl min(-1) at 15 degrees C, 1.12 microl min(-1) at 25 degrees C, and 3.03 microl min(-1) at 40 degrees C. At 15, 25 and 40 degrees C, this was 343, 73 and 10 times below the values of the highly active bees, respectively. The Q(10) value of the resting bees, however, was not constant but varied in a U-shaped manner with ambient temperature. It decreased from 4.24 in the temperature range 11-21 degrees C to 1.35 in the range 21-31 degrees C, and increased again to 2.49 in the range 30-40 degrees C. We conclude that attempts to describe the temperature dependence of the resting metabolism of honeybees by Q(10) values can lead to considerable errors if the measurements are performed at only two temperatures. An acceptable approximation can be derived by calculation of an interpolated Q(10) according to the exponential function (V(O(2))=0.151 x 1.0784(T(a))) (interpolated Q(10)=2.12).     

Effect of temperature on the settlement choice and photophysiology of larvae from the reef coral Stylophora pistillata

To better understand the consequences of climate change for scleractinian corals, Stylophora pistillata was used to test the effects of temperature on the settlement and physiology of coral larvae. Freshly released larvae were exposed to temperatures of 23 degrees C, 25 degrees C (ambient), and 29 degrees C at light intensities of approximately 150 micromol photons m(-2) s(-1). The effects were assessed after 12 h as settlement to various substrata (including a choice between crustose coralline algae [CCA] and limestone) and as maximum quantum yield of PSII (F(v)/F(m)) in the larvae versus in their parents. Regardless of temperature, 50%-73% of the larvae metamorphosed onto the plastic of the incubation trays or in a few cases were drifting in the water, and 14% settled on limestone. However, elevated temperature (29 degrees C) reduced the percentage of larvae swimming by 81%, and increased the percentage choosing CCA nearly 7-fold, both relative to the outcomes at 23 degrees C. Because temperature did not affect settlement on limestone or plastic, increased settlement on CCA reflected temperature-mediated choices by larvae that otherwise would have remained swimming. Interestingly, F(v)/F(m) was unaffected by temperature, but it was 4% lower in the larvae than in the parents. These results are important because they show that temperature can affect the settlement of coral larvae and because they reveal photophysiological differences between life stages that might provide insights into the events associated with larval development.     

The effect of temperature on larval pre-settlement duration and metamorphosis for the sponge, <Emphasis Type="Italic">Rhopaloeides odorabile</Emphasis>

Rising sea temperatures may potentially affect the dispersive larval phase of sessile marine invertebrates with consequences for the viability of adult populations. This study demonstrated that the planktonic larvae of Rhopaloeides odorabile, a common Great Barrier Reef sponge, survived and metamorphosed when exposed to temperatures up to 9°C above the annual maximum (~29°C). Planktonic larval duration of 54 h, at ambient temperatures (~28°C), were reduced to 18 h for larvae exposed to elevated temperatures (32–36°C). Moreover, at ambient temperatures larvae began metamorphosing after 12 h, but at 32–36°C this reduced to only 2 h. Larvae survived and could still metamorphose at temperatures as high as 38°C, but were no longer functional at 40°C. These results imply that predicted increases in sea surface temperature may reduce planktonic larval duration and dispersal capabilities, thereby contributing to population subdivision of the species.     

Relative susceptibility of Tribolium confusum life stages exposed to elevated temperatures

Methyl bromide, a space fumigant used in food-processing facilities, may be phased out in the United States by 2005. The use of elevated temperatures or heat treatment is gaining popularity as a methyl bromide alternative. During heat treatment, the temperature of the whole food-processing facility, or a portion of it, is raised and held between 50 and 60 degrees C for 24-36 h to kill stored-product insects. We determined time-mortality responses of the confused flour beetle, Tribolium confusum (Jacquelin du Val), eggs, young larvae, old larvae, pupae, and adults exposed to six constant temperatures between 46 and 60 degrees C. Responses of all five insect stages also were measured using exposure times of 160, 40, and 12 min at 46, 50, and 60 degrees C, respectively. Time-mortality responses of all T. confusum life stages increased with an increase in exposure time and temperature. Both time-mortality and fixed time responses showed eggs and young larvae to be most susceptible at elevated temperatures and old larvae to be least susceptible. Our results suggest that old larvae should be used as test insects to gauge heat treatment effectiveness, because heat treatment aimed at controlling old larvae should be able to control all other T. confusum life stages. Besides providing baseline data for successful use of heat treatments, time-mortality data collected at the six temperatures can be used for developing thermal death kinetic models for this species to predict mortality during actual facility heat treatments.     

Time-mortality relationships for Tribolium castaneum (Coleoptera: Tenebrionidae) life stages exposed to elevated temperatures

The use of elevated temperatures (> or = 40-60 degrees C) or heat treatments for managing insects in food-processing facilities is a viable alternative to space fumigation with methyl bromide. Quantitative data are lacking on the responses of life stages of the red flour beetle, Tribolium castaneum (Herbst), an important pest of food-processing facilities worldwide, to elevated temperatures used during heat treatments. We determined time-mortality relationships for eggs, young (neonate) larvae, old larvae, pupae, and adults of T. castaneum, exposed to constant temperatures of 42, 46, 50, 54, 58, and 60 degrees C. Generally, mortality of each stage increased with an increase in temperature and exposure time. Young larvae were the most heat-tolerant stage, especially at temperatures > or = 50 degrees C. Exposure for a minimum of 7.2 h at > or = 50 degrees C was required to kill 99% of young larvae, whereas the other stages required < or = 1.8 h. Heat treatments that control young larvae should control all other stages of T. castaneum, and young larvae should be used as test insects to evaluate efficacy against T. castaneum during an actual facility heat treatment. These results provide the basis for successful use of elevated temperatures for management of T. castaneum life stages associated with food-processing facilities.     

Reproductive performance of Tribolium castaneum (Coleoptera: Tenebrionidae) exposed to the minimum heat treatment temperature as pupae and adults

Managing stored-product insect pests by heating the ambient air of a food-processing facility to high temperatures (50-60 degrees C), also referred to as heat treatment, is an effective technology that has been used since the early 1900s. The minimum temperature during heat treatment for effective disinfestation is 50 degrees C. The effect of sublethal exposures to 50 degrees C on the reproductive performance of stored-product insects associated with food-processing facilities is unknown. The red flour beetle, Tribolium castaneum (Herbst), is a pest commonly found in food-processing facilities worldwide. The adverse effects on fecundity, egg-to-adult survival, and progeny production of T. castaneum exposed as 1-d-old pupae and 2-wk-old adults to 50 degrees C for 60 and 39 min, respectively, were determined in the laboratory. Pupae and adults exposed for the same time periods at 28 degrees C served as the control treatment. Four possible reciprocal crosses were carried out among adults from the heat-treated (50 degrees C) and control (28 degrees C) treatments. The number of eggs produced during the first 2 wk of adult life, survival of these eggs to adulthood, and adult progeny production after 2 and 8 wk of oviposition in treatments representing all four reciprocal crosses were determined. Fecundity, egg-to-adult survival, and adult progeny production decreased by 17-63, 52-63, and 66-78%, respectively, when males, females, and both males and females were exposed to 50 degrees C. These effects were relatively more pronounced in treatments in which pupae were exposed to the high temperature compared to adults, and in exposed females than in males. The impaired reproductive performance in T. castaneum pupae and adults surviving sublethal exposures to the minimum heat treatment temperature is valuable for understanding population rebound following a heat treatment intervention.     

Influence of hyperthermia on gamma-ray-induced mutation in V79 cells

Asynchronously growing V79 cells were assayed for mutation induction following exposure to hyperthermia either immediately before or after being irradiated with 60Co gamma rays. Hyperthermia exposures consisted of either 43.5 degrees C for 30 min or 45 degrees C for 10 min. Each of these heat treatments resulted in a survival level of 42%. For all sequences of combined treatment with hyperthermia and radiation, cell killing by gamma rays was enhanced. Mutation induction by gamma rays was enhanced when heat preceded gamma irradiation, but no increase was observed when heat was given after gamma exposures. Treatment at 45 degrees C for 10 min gave a higher yield in mutants at all gamma doses studied compared to treatment at 43.5 degrees C for 30 min. When heat-treated cells were incubated for different periods before being exposed to gamma rays, thermal enhancement of radiation killing was lost after 24 h. In contrast, only 5-6 h incubation was needed for loss of mutation induction enhancement.     

Rapid responses to high temperature and desiccation but not to low temperature in the freeze tolerant sub-Antarctic caterpillar Pringleophaga marioni (Lepidoptera,Tineidae)

A broad definition of rapid cold hardening (RCH) is that it is the process whereby insects increase their survival of a sub-zero temperature after a brief (h) pre-exposure to a less severe low temperature. The effects of various pre-treatments on survival of two h at -7.9 degrees C were investigated in the freeze tolerant sub-Antarctic caterpillar Pringleophaga marioni (Lepidoptera: Tineidae), the first time RCH has been investigated in a freeze tolerant arthropod. All caterpillars froze when exposed to -7.9 degrees C, and none of the low temperature pre-treatments (-5, 0, 5 and 15 degrees C, as well as -5 degrees C and 0 degrees C with a delay before freezing) nor slow cooling (0.1 degrees C/min) elicited any improvement in survival of -7.9 degrees C as compared to controls. However, high temperature treatments (25, 30 and 35 degrees C), desiccation and acclimation for 5 days at 0 degrees C did result in significant increases in survival of the test temperature, possibly as a result of heat shock protein production. Haemolymph osmolality was elevated only by the 35 degrees C pre-treatment. It is suggested that the unpredictable environment of Marion Island means that P. marioni must always be physiologically prepared to survive cold snaps, and that this year-round cold hardiness therefore supersedes a rapid cold hardening response.     

Effects of summer frost exposures on the cold tolerance strategy of a sub-Antarctic beetle

The sub-Antarctic beetle Hydromedion sparsutum (Coleoptera, Perimylopidae) is common locally on the island of South Georgia where sub-zero temperatures can be experienced in any month of the year. Larvae were known to be weakly freeze tolerant in summer with a mean supercooling point (SCP) around -4 degrees C and a lower lethal temperature of -10 degrees C (15min exposure). This study investigated the effects of successive freezing exposures on the SCP and subsequent survival of summer acclimatised larvae. The mean SCP of field fresh larvae was -4.2+/-0.2 degrees C with a range from -1.0 to -6.1 degrees C. When larvae were cooled to -6.5 degrees C on 10 occasions at intervals of 30min and one and four days, survival was 44, 70 and 68%, respectively. The 'end of experiment' SCP of larvae surviving 10 exposures at -6.5 degrees C showed distinct changes and patterns from the original field population depending on the interval between exposure. In the 30min interval group, most larvae froze between -6 and -8 degrees C, a depression of up to 6 degrees C from the original sample; all larvae were dead when cooling was continued below the SCP to -12 degrees C. In the one and four day interval groups, most larvae froze above -6 degrees C, showing no change as a result of the 10 exposures at -6.5 degrees C. As with the 30min interval group, some larvae froze below -6 degrees C, but with a wider range, and again, all were dead when cooled to -12 degrees C. However, in the one and four day interval groups, some larvae remained unfrozen when cooled to -12 degrees C, a depression of their individual SCP of at least 6 degrees C, and were alive 24h after cooling. In a further experiment, larvae were cooled to their individual SCP temperature at daily intervals on 10 occasions to ensure that every larva froze every day. Most larvae which showed a depression of their SCP of 2-4 degrees C from their day one value became moribund or died after six or seven freezing events. Survival was highest in larvae with SCPs of -2 to -3 degrees C on day one and which froze at this level on all 10 occasions. The results indicate that in larvae in which the SCP is lowered following sub-zero exposure, the depression of the SCP is greatest in individuals that do not actually freeze. Further, the data suggest that after successive frost exposures in early winter the larval population may become segregated into two sub-populations with different overwintering strategies. One group consists of larvae that freeze consistently in the temperature range from -1 to -3 degrees C and can survive multiple freeze-thaw cycles. A second group with lower initial SCPs (around -6 degrees C), or which fall to this level or lower (down to -12 degrees C) after freezing on one or more occasions, are less likely to freeze through extended supercooling, but more likely to die if freezing occurs.     

Persistence of sleep-temperature coupling after suprachiasmatic nuclei lesions in rats

The suprachiasmatic nucleus (SCN) regulates the circadian rhythms of body temperature (T(b)) and vigilance states in mammals. We studied rats in which circadian rhythmicity was abolished after SCN lesions (SCNx rats) to investigate the association between the ultradian rhythms of sleep-wake states and brain temperature (T(br)), which are exposed after lesions. Ultradian rhythms of T(br) (mean period: 3.6 h) and sleep were closely associated in SCNx rats. Within each ultradian cycle, nonrapid eye movement (NREM) sleep was initiated 5 +/- 1 min after T(br) peaks, after which temperature continued a slow decline (0.02 +/- 0.006 degrees C/min) until it reached a minimum. Sleep and slow wave activity (SWA), an index of sleep intensity, were associated with declining temperature. Cross-correlation analysis revealed that the rhythm of T(br) preceded that of SWA by 2-10 min. We also investigated the thermoregulatory and sleep-wake responses of SCNx rats and controls to mild ambient cooling (18 degrees C) and warming (30 degrees C) over 24-h periods. SCNx rats and controls responded similarly to changes in ambient temperature. Cooling decreased REM sleep and increased wake. Warming increased T(br), blunted the amplitude of ultradian T(br) rhythms, and increased the number of transitions into NREM sleep. SCNx rats and controls had similar percentages of NREM sleep, REM sleep, and wake, as well as the same average T(b) within each 24-h period. Our results suggest that, in rats, the SCN modulates the timing but not the amount of sleep or the homeostatic control of sleep-wake states or T(b) during deviations in ambient temperature.     

Pressure- vs. heat-induced bacterial stress in cooked poultry sausages: a preliminary study

Vacuum-packaged poultry cooked sausages were pressure-treated at 500 MPa by combinations of time (5-45 min) and temperature (2-80 degrees C) and later stored at 6-8 degrees C for 12 we. Mesophile and psychrotrophe counts were determined 1 d, 3, 6, 9 and 12 we after treatment and compared with those of cooked sausages pasteurized at 80-85 degrees C for 40 min. Both pressure and heat treatments offer great possibilities for preservation. Sausages pressurized at 65 degrees C for 15 min showed mesophile numbers below 2 log cfu g(-1) throughout the chill storage. Pressurization, unlike heat treatment, causes a reversible bacterial stress. Thus, injured cells recovered during storage and, at 6 and 12 we, after a temperature abuse (room temperature for approx. 24 h), counts increased up to 6.5 - 7.5 log units. Psychrotrophes were more sensitive to both treatments; no growth was detected the day after (a lethality of more than 4 log units).     

Variations des zymogrammes estérasiques chez les larves de Palaemon serratus soumises à différentes durées de choc thermique

Palaemon serratus at larval stage 2, acclimatized at 16°, were subjected to a temperature increase of 15° for periods of 5, 20 or 40 min with or without return to the initial temperature for 12 h. The soluble protein concentration of larvae subjected to a thermal shock of 20 min duration is lower than in control larvae. Total esterase-2C activity per mg of soluble protein after a thermal shock of 20 min duration is less than in control larvae but, in contrast with larvae subjected to a shock of 40 min duration, the initial activity is restored after 12 hours. Esterase-2C activity zymograms, after polyacrylamide gradient gel electrophoresis, show twelve isozymes. The activity of each isozyme examined varies according to the duration of the thermal shock.