BACTERIOLOGICAL ASPECTS OF THE EVALUATION OF ADEQUACY OF PASTEURIZATION

Increased interest in high-temperature, short-time pasteurization of various dairy products has emphasized the need for methods to determine the adequacy of pasteurization. One such method is described, but there is need for additional information. The thermal death time curves of various pathogens should be determined in different dairy products. A suitable heat resistant test organism such as Micrococcus MS-102 should be selected, approved by health officials and made available to others for controlled studies. Data should be accumulated so that curves could be prepared to show any combination of time and temperature which would result in adequate pasteurization.

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Influences of High-Temperature Short-Time Endurance Performance of Heat Resistant Steel for Ultra Supercritical Units

Materials Science Forum ◽

10.4028/www.scientific.net/msf.749.361 ◽

2013 ◽

Vol 749 ◽

pp. 361-365

Author(s):

Hua Tang ◽

Feng Xiao ◽

Jian Sheng Ding ◽

Zhi Hong Li

Keyword(s):

High Temperature ◽

Grain Boundary ◽

Experimental Testing ◽

Endurance Performance ◽

Second Phase ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Heat Resistant ◽

High Temperature Short Time ◽

Short Time

Heat-resistant steel (12%wt. Cr) used in the ultra supercritical set blade was quenched and tempered by vacuum heat treatment furnace, the mechanical properties and metallographic structures at room temperature can meet the specific requirements. However, there are some problems existed on high-temperature short-time lasting performance. To improve the high temperature endurance performance of materials, the experimental testing and analysis were carried out fro different types of specimen. The research showed that short-time rupture is a kind of creep fracture, and short lasting strength was closely related to test temperatures between laths and grain boundary and carbide coarsening. Energy spectrum analysis revealed that cast in the hole had high B element content (19.98%wt.), which meant grain boundaries of the B at high temperature began to migrate and form in the crystal B in that second phase particles are contained, and grain boundary strength was obviously decreased. The enduring high temperature experiment indicated that the strength were declined rapidly and fractured suddenly at high temperature.

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Efficacy of Pasteurization Conditions for the Inactivation of Mycobacterium avium subsp. paratuberculosis in Milk

Journal of Food Protection ◽

10.4315/0362-028x-67.12.2719 ◽

2004 ◽

Vol 67 (12) ◽

pp. 2719-2726 ◽

Cited By ~ 53

Author(s):

J. R. STABEL ◽

A. LAMBERTZ

Keyword(s):

High Temperature ◽

Mycobacterium Avium ◽

Dairy Products ◽

Mycobacterium Avium Subsp ◽

High Temperature Short Time ◽

Mycobacterium Avium Subsp Paratuberculosis ◽

High Concentrations ◽

Ultrahigh Temperature ◽

Short Time ◽

Cheese Production

Mycobacterium avium subsp. paratuberculosis, the causative agent of a chronic enteritis in ruminants (Johne's disease), has been linked to Crohn's disease in humans. This microorganism is shed by infected animals primarily in the feces but is also shed in the milk at much lower levels. Therefore, dairy products from infected animals may be one mode of transmission of this animal pathogen. This study was designed to evaluate the effectiveness of the holder and high-temperature short-time pasteurization standards on the destruction of M. paratuberculosis. One hundred eighty experiments were conducted in this study using a slug-flow pasteurizer unit and a laboratory scale pasteurizer unit. Ultrahigh-temperature milk was inoculated at two concentrations, 108 and 105 CFU/ml, with three different field strains of M. paratuberculosis. Five different time-temperature combinations were evaluated: 62.7°C for 30 min, 65.5°C for 16 s, 71.7°C for 15 s, 71.7°C for 20 s, and 74.4°C for 15 s. Three replicates of each experiment were run for the pasteurizer unit, time-temperature combination, and strain of M. paratuberculosis. Treatment of milk regardless of bacterial strain or pasteurizer unit resulted in an average 5.0- and 7.7-log kill for the low and high concentrations of inoculum, respectively. Milk treated for cheese production (65.5°C for 16 s) resulted in a much lower and more variable kill. Results from this study indicate that the current U.S. minimum standards for batch and high-temperature short-time pasteurization of grade A milk significantly reduced the survivability of M. paratuberculosis, but some bacteria survived subpasteurization heat treatment of milk used for cheese manufacture.

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Heat Resistance of Fungi Isolated from Frozen Blueberries

Journal of Food Protection ◽

10.4315/0362-028x-71.10.2030 ◽

2008 ◽

Vol 71 (10) ◽

pp. 2030-2035 ◽

Cited By ~ 14

Author(s):

YUTAKA KIKOKU ◽

NOBUHIRO TAGASHIRA ◽

HIROYUKI NAKANO

Keyword(s):

Thermal Resistance ◽

Heat Resistance ◽

Thermal Inactivation ◽

Heat Resistant ◽

Death Time ◽

Naturally Occurring ◽

Thermal Death ◽

D Values ◽

Thermal Death Time

This study dealt with the isolation, characterization, and identification of the fungal microflora of frozen blueberries imported from Canada. The thermal inactivation rates of the rarely studied isolated heat-resistant molds, Devriesia spp. and Hamigera striata, in naturally and artificially contaminated blueberry slurries were also determined. The D-values of naturally contaminating Devriesia spp. at 70, 80, 85, and 90°C were 714, 114, 44.4, and 14.1 min, respectively. The D-values of H. striata at 70, 80, 85, and 90°C were 909, 286, 42.6, and 10.3 min, respectively. The z-values calculated from the thermal death time curves were 11.0 and 6.9°C for Devriesia spp. and H. striata, respectively. Results also showed that in both test mold species, the naturally occurring molds had significantly higher thermal resistance than did the artificially contaminated counterparts. The results established by this study may be used by blueberry processors to prevent losses due to spoilage caused by the heat-resistant microorganisms.

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PHYSIOLOGICAL CHARACTERISTICS OF ENTEROPATHOGENIC AND NON-PATHOGENIC COLIFORM BACTERIA ISOLATED FROM CANADIAN PASTEURIZED DAIRY PRODUCTS1

Journal of Milk and Food Technology ◽

10.4315/0022-2747-32.3.102 ◽

1969 ◽

Vol 32 (3) ◽

pp. 102-109 ◽

Cited By ~ 1

Author(s):

Ho-Yu Yang ◽

G. A. Jones

Keyword(s):

Dairy Products ◽

Skim Milk ◽

Rapid Test ◽

Coliform Bacteria ◽

Triphenyltetrazolium Chloride ◽

E Coli ◽

Death Time ◽

Thermal Death ◽

Thermal Death Time ◽

Valid Criterion

Three enteropathogenic Escherichia coli serotypes (PE) were compared with three non-pathogenic E. coli strains (E) and three Enterobacter aerogenes strains (A) on the basis of their biochemical, thermal death time, and low temperature growth characteristics. All nine strains were isolated from Canadian pasteurized dairy products. It was not possible to differentiate consistently between the PE and E strains from the results of any biochemical tests performed. Differentiation was achieved, however, on the basis of differences in colonial morphology of the strains when grown on Tergitol-7 agar containing 0.004% 2, 3, 5-triphenyltetrazolium chloride; the PE strains produced rough or intermediate rough colonies on this medium, whereas the E and A strains produced smooth or mucoid colonies. Thermal death time studies showed that one or more of the E strains might survive a commercial high temperature process if the number of cells present in the raw milk were unusually large; the PE and A strains were relatively heat sensitive and would be unlikely to survive pasteurization. z-Values found for the strains varied from 9.6 to 16.5, but the magnitude of these values was not directly correlated with the identity of particular groups of strains. Viable counts of the E strains suspended in skim milk at 7 C decreased with time; counts of the A strains and of one of the PE strains declined during the first 2 to 4 days of storage but thereafter increased rapidly. One PE strain grew only weakly under these conditions but the third showed a remarkable capacity for rapid initiation of fast growth. When cells were suspended in skim milk at −28 C, viable counts of all nine strains decreased during storage. It was concluded that particular significance can be attached to the capacity of the PE strains to multiply in skim milk held at 7 C if the serological evidence obtained is a valid criterion of their potential enteropathogenicity. The results emphasize the need for a simple and rapid test to detect enteropathogenic E. coli contamination of dairy products, and it is suggested that a cultural test, using Tergitol-7 agar containing 2, 3, 5-triphenyltetrazolium chloride as a differential medium, might be developed for this purpose.

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Diversity Assessment of Heat Resistance of Listeria monocytogenes Strains in a Continuous-Flow Heating System

Journal of Food Protection ◽

10.4315/0362-028x-72.5.999 ◽

2009 ◽

Vol 72 (5) ◽

pp. 999-1004 ◽

Cited By ~ 6

Author(s):

STIJN van der VEEN ◽

ARJEN WAGENDORP ◽

TJAKKO ABEE ◽

MARJON H. J. WELLS-BENNIK

Keyword(s):

High Temperature ◽

Listeria Monocytogenes ◽

Continuous Flow ◽

Foodborne Pathogen ◽

Brain Heart Infusion ◽

Brain Heart Infusion Broth ◽

Heat Resistant ◽

High Temperature Short Time ◽

Diversity Assessment ◽

Short Time

Listeria monocytogenes is a foodborne pathogen that has the ability to survive relatively high temperatures compared with other nonsporulating foodborne pathogens. This study was performed to determine whether L. monocytogenes strains with relatively high heat resistances are adequately inactivated in a high-temperature, short-time pasteurization process (72°C for 15 s). To obtain heat-resistant strains, 48 strains were exposed to 55°C for up to 3 h. The energy of activation constant and inactivation constant of strains that survived best (strains 1E and NV8) were subsequently determined in a continuous-flow-through system. Strain Scott A was taken along as a reference. The 3 strains were cultured in whole milk and in brain heart infusion broth at 30 and 7°C. Strains 1E and NV8 were significantly more heat resistant than was strain Scott A after growth in brain heart infusion broth at 30°C and after growth in milk at 7°C. From the inactivation parameters, it was calculated that exposure to high-temperature, short-time pasteurization (72°C for 15 s) will result in 12.1-, 14.2-, and 87.5-log reductions for the strains 1E, NV8, and Scott A, respectively. These results demonstrate that industrial pasteurization conditions suffice to inactivate the most heat-resistant L. monocytogenes strains tested in this study.

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Heat Resistance of Listeria monocytogenes Scott A and HAL 957E1 in Various Liquid Egg Products†

Journal of Food Protection ◽

10.4315/0362-028x-58.11.1211 ◽

1995 ◽

Vol 58 (11) ◽

pp. 1211-1214 ◽

Cited By ~ 22

Author(s):

F. M. BARTLETT ◽

A. E. HAWKE

Keyword(s):

Listeria Monocytogenes ◽

Egg Yolk ◽

Death Time ◽

High Temperature Short Time ◽

Egg Products ◽

Liquid Whole Egg ◽

The Individual ◽

Thermal Death Time ◽

Short Time ◽

Whole Egg

The thermal destruction of Listeria monocytogenes Scott A and HAL 957E1 (an egg isolate) was determined in five liquid egg products. The egg products used were liquid whole egg (LWE), liquid whole egg with 10% NaCl (LWEN), liquid whole egg with 10% sucrose (LWES), egg yolk with 10% NaCl (EYN), and egg yolk with 10% sucrose (EYS). Each of these products was inoculated with the individual strains of L. monocytogenes at initial populations of 106 colony-forming units (CFU)/ml and exposed to temperatures of up to 70°C for various periods of time from which thermal death time (TDT) curves were constructed. The Scott A strain tended to be more heat resistant than the egg isolate, HAL 957E1. The sensitivity of both strains to heating was influenced by the type of egg product in which they were suspended. The highest rates of kill were noted in LWE, while survival was best in those products supplemented with NaCl (LWEN and EYN). For the nonsalted products, time and temperature combinations equivalent to those required for the high-temperature short-time (HTST) pasteurization of liquid egg achieved 1.7 to 4.4 log-unit reductions of L. monocytogenes populations, while reductions for the salted products were only 0.2 to 0.6 log units. These results suggest that current HTST pasteurization conditions for liquid egg will not ensure a Listeria-free product, especially with products supplemented with NaCl.

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Predictive Modeling of Alkaline Phosphatase Inactivation in a High-Temperature Short-Time Pasteurizer

Journal of Food Protection ◽

10.4315/0362-028x-57.5.424 ◽

1994 ◽

Vol 57 (5) ◽

pp. 424-430 ◽

Cited By ~ 19

Author(s):

R. C. MCKELLAR ◽

H. W. MODLER ◽

H. COUTURE ◽

A. HUGHES ◽

P. MAYERS ◽

...

Keyword(s):

Alkaline Phosphatase ◽

High Temperature ◽

Predictive Modeling ◽

Dairy Products ◽

Residual Activity ◽

Lethal Effect ◽

Predictive Equations ◽

High Temperature Short Time ◽

Whole Milk ◽

Short Time

In order to support regulations directed towards ensuring the safety of heat processed dairy products, data on inactivation of alkaline phosphatase (AP) in whole milk in a pilot plant high-temperature short-time (HTST) pasteurizer were obtained. A Computer program was designed to calculate the integrated lethal effect, or pasteurization effect (PE), at temperatures of 60 to 74°C and with holding tubes for 3 to 60 s. An equation was derived which related values of PE to log % residual activity (r2 of 0.964). These results suggest that predictive equations based on PE could be used to assess the effectiveness of commercial pasteurization processes.

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The old and the large may suffer disproportionately during episodes of high temperature: evidence from a keystone zooplankton species

Conservation Physiology ◽

10.1093/conphys/coaa038 ◽

2020 ◽

Vol 8 (1) ◽

Cited By ~ 1

Author(s):

Tim Burton ◽

Sigurd Einum

Keyword(s):

Body Size ◽

High Temperature ◽

Temperature Tolerance ◽

The Body ◽

Acute Tolerance ◽

Zooplankton Species ◽

Time Curve ◽

Death Time ◽

Thermal Death ◽

Thermal Death Time

Abstract Widespread declines in the body size of aquatic ectotherms have been attributed to the poorer ability of older, larger individuals to tolerate high temperature. Here, using the thermal death time curve framework, we investigate the relationship between temperature tolerance and size/age by measuring the change in heat tolerance of the keystone zooplankton species Daphnia magna across a range of temperature intensities (and hence exposures of varying duration) among individuals that differed up to 3-fold in size and thus varied in age also. Across the gradient of exposure temperatures, younger, smaller individuals were more tolerant than older, larger individuals. This suggests that the young and the small may be better equipped to withstand temperature challenges that are both intense/brief and more moderate/prolonged. Our study generalizes results obtained from more acute tolerance assays, providing physiological evidence consistent with the observed reductions in ectotherm body size as a response to warming in aquatic systems.

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721. An analysis of the performance of an ultra-high-temperature milk sterilizing plant: II. Calculation of the bactericidal effectiveness

Journal of Dairy Research ◽

10.1017/s002202990000933x ◽

1958 ◽

Vol 25 (2) ◽

pp. 324-337 ◽

Cited By ~ 21

Author(s):

H. Burton

Keyword(s):

Heat Treatment ◽

High Temperature ◽

Treatment Plant ◽

Flow Time ◽

Death Time ◽

Thermal Death ◽

Continuous Heat Treatment ◽

Micro Organisms ◽

Thermal Death Time ◽

Continuous Heat

The purpose of this paper is to show how the performance of a continuous heat-treatment plant may be predicted from the temperature distribution and the flow time distributions obtained as described in the first paper of this series (1), using thermal death-time characteristics appropriate to the micro-organisms of greatest importance. The calculations are carried out using the data obtained for the plant described in the previous paper, and they provide an estimate of the bactericidal effectiveness to be expected from that plant.

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