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Experimental Approaches to Poultry Meat Surface Pasteurization by Condensing Vapors
Experimental Approaches to Poultry Meat Surface Pasteurization by Condensing Vapors A. A. KLOSE AND H. G. BAYNE Western Regional Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Albany, California 94710 (Received for publication October 23, 1969) INTRODUCTION
A
Obvious avenues for control of salmonellae and other pathogens include 1) elimination of the microorganisms at one or more stages of production and processing, 2) inhibition of growth of existing low
levels of the microorganisms, and 3) destruction of the microorganisms on the final product. This paper is concerned with the last avenue mentioned, although this is not to discount the need and potential for implementing elimination of the microorganisms at their sources and inhibition of growth at all stages of utilization. We are further limiting our attention to surface pasteurization, because of the following considerations. Sterile conditions generally exist in the interior of poultry meat. Moreover, under normal cooking conditions, the interior of the meat should reach and exceed a temperature of 160°F., which should destroy salmonellae and eliminate any health hazards (Wilkinson et al., 1965). Finally the major hazard as we have noted and as documented by detailed U.S. Public Health reports of Salmonella food poisoning outbreaks, is cross-contamination between contaminated raw product and cooked products or products not requiring further cooking. Previously reported attempts to achieve surface pasteurization by dipping poultry in bactericidal solutions have met with little or no success. Wabeck et al. (1968) concluded, from extensive tests of sodium hypochlorite solutions on chicken drumsticks, that salmonellae inoculated at 100 cells per ml. on drumsticks were only reduced tenfold by constantly flowing 20 p.p.m. chlorine solutions. A 20 p.p.m. chlorine solution destroyed 1,000 salmonellae per ml. within 30 minutes when organic matter was absent, but available
504
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MONG the many animal derived food -products that have been implicated in Salmonella-caused food poisoning outbreaks, chicken and turkey meat have been involved in a substantial percentage of the cases. For example, in 1967, out of 25 outbreaks involving 5,600 people reported by the Salmonella Surveillance Reports, five outbreaks involving 2,295 people were traced to contaminated turkey meat. These cases arose mainly in institutional type feeding, so we may suspect that they might have been caused by poor handling practices in the institutional kitchens. However, the fact remains that poultry represents a widespread and ever present reservoir of salmonellae on the farm, in the processing plant (Bryan, 1965), and in the finished product (Sadler and Corstvet, 1965) as it moves to the point of consumption to be cooked. Since subjection of poultry meat products to an adequate end point cooking temperature will destroy all potential pathogenic microorganisms, it is reasonable to assume that the critical hazard lies in cross contamination between contaminated raw poultry, food handling surfaces, and food products that will not receive pathogenkilling heat treatment between contamination and consumption.
POULTRY SURFACE PASTEURIZATION
GENERAL EXPERIMENTAL PROCEDURES1 A major part of this research was carried out with commercial chicken fryer drumsticks. This raw material was fresh chilled, purchased from a retail market supplied by one processing plant, and 1 Reference to a company or product name does not imply approval or recommendation of the product by the U. S. Department of Agriculture to the exclusion of others that mav be suitable.
generally had consumed 2 to 4 days of its refrigerated shelf life when it was subjected to the pasteurization treatment. Treated and control drumsticks were held in individual polyethylene bags at 3°C. for determination of their remaining days of satisfactory refrigerated shelf life. End point was the time at which an incipient bacterial spoilage odor had developed in the meat. Development of fluorescence when exposed to ultraviolet radiation was also followed in all samples. Estimations of the number of viable microorganisms in the drumsticks and whole birds, initially and after the pasteurizing treatment, were determined in the following manner. Stock solution—Inocula. Two 250 ml. flasks containing 50 ml. of Trypticase Soy Broth and 2% Yeast Extract (TSB-YE) were inoculated with a culture of S. typhimurium Tm-1 (from a TSA-YE slant). The flasks were placed on a shaker in the 28°C. incubator and the culture allowed to grow for 48 hours. They were then removed, the contents decanted into small sterile centrifuge cups and centrifuged for 20 minutes at approximately 15,000 g. The broth was decanted and the cells were washed with sterile demineralized water; the process of centrifuging was done twice. The final cell pack was then suspended in 100 ml. of sterile demineralized water and stored in the refrigerator (5°C). The stock solution was found to contain 4.0 X10 9 cells per ml. Inoculation of drumsticks or birds with S. typhimurium Tm-1. 1.0 ml. of stock solution was diluted in 1,000 ml. sterile demineralized water to give a count of approximately 106. The birds or drumsticks were placed therein for 10 minutes, removed and allowed to drain. They were stored for one hour at 3°C. Counts were made of the inoculum by making serial dilutions in TSB-YE and spread-
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chlorine was rapidly depleted in the presence of poultry tissue. Sixty p.p.m. chlorine solution imparted an off-flavor and odor aftef a 4-hour application to thawing meat. Previously, Thomson et al. (1967) had also shown that sprays of chlorine solutions at 100 and 200 p.p.m. produced only small reduction in numbers of Salmonella typhimurium inoculated on chicken carcasses. Sprays of /3-propiolactone, succinic acid, and citric acid had only minor effects. Dawson et al. (1963) measured the extent of surface pasteurization of half chicken-fryers effected by slow agitation in water at temperatures ranging from 135°F. <57°C.) to 155°F. (68°C.) and for times from one to ten minutes. Total bacteria counts were reduced to 1/10-1/1,000 of control values; one to two log reductions with extensions of shelf life at 34°F. (1°C.) of about 4 days were accomplished in many cases. This paper describes several treatments that pasteurize poultry meat surfaces, all of which involve a condensation of distilling vapors from boiling liquid(s) onto the poultry meat surface for specified times. Relative effectiveness was estimated by determining reduction in bacterial numbers and extension of chilled shelf life. Studies included determination of ease of removal of residual solvents, and organoleptic acceptability of the cooked products.
505
506
A. A. K L O S E AND H. G. B A Y N E
plating 0.1 ml. aliquots in duplicate. Plates were incubated at 28°C. for 24 or more hours, removed and counted. Sampling controls and treated birds or drumsticks. (A). Control and treated birds were covered with 500 ml. sterile demineralized water in Cryovac bags and allowed to stand for 5 to 10 minutes with severe intermittent agitation. 1.0 ml. of this new suspension was then serially diluted and 0.1 ml. aliquots of each dilution in duplicate were plated onto T S A - Y E and BGA (Brilliant Green Agar), spread, incubated a t 28°C. a n d counted. 0.5 ml. aliquots of the undiluted suspensions were also used. (B). Drumsticks, of 80-100 grams weight, were placed in whirlbags and covered with 100 ml. or (later) 25 ml.
T S B - Y E . The resulting agitated suspensions were diluted and plated as described for the whole birds, except t h a t 0.5 ml. or 1.0 ml aliquots of the undiluted suspensions were plated directly. Drumsticks were pasteurized b y condensing vapors from solvents introduced into a 12-liter, round bottomed, 3-neck Pyrex flask, heated on its lower surface by the lower heating element of a 2-element hemispherical electrical heating mantle controlled through a variable voltage transformer (Figure 1). T h e central neck was used interchangeably, either to insert a thermometer to record the condensing temperature of the liquid system, or to introduce and suspend the drumstick b y a wire hook in the vapor phase above the boiling liquid. A thermometer well was
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FIG. 1. Flask used for pasteurization of drumsticks.
507
POULTRY SURFACE PASTEURIZATION
RESULTS AND DISCUSSION
The first liquids tested were mixtures of acetone and water, which produced substantial reductions in total bacterial count and extensions of chilled shelf life (Table 1). The use of acetone was not considered
TABLE 1.—Pasteurizing effect of condensing vapors (70°C.) from 25% acetone—75% water solution on chicken drumsticks Exposure to Total bacterial Shelf life at 3 ° C , condensing vapor count per ml. beyond exposure (minutes) of diluent (days) 0 0 S 10
8X10 7 1X10 8 6X10 3 6X10 1
<4 <4 15 21
promising, however, because of the extreme difficulty of removing the last organoleptically detectable trace of the solvent from the meat. Tests of isopropyl alcohol on drumsticks resulted in almost complete elimination of surface bacterial contamination within 4 minutes, and 16 days extension of shelf life (Table 2). An azeotropic mixture of trichloroethylene and water (Table 3) condensing at a much lower temperature (73°C.) than isopropyl alcohol, gave substantial bacterial kills within 4 to 8 minutes. Attempts to remove the last organoleptically detectable traces of these solvents from the drumsticks met with only limited success (Table 4). Soaking the drumsticks treated with isopropyl alcohol for 4 minutes in 3°C. water for as long as 6 hours left definite traces of isopropyl alcohol odor in the freshly roasted drumsticks, and even 24 hours' soaking left a faint trace. Vacuum treatment of trichloroethylene samples reduced the solvent level to a point where an odor panel was unable to distinguish solvent treated samples from controls in triangle comparisons. This difference in ease of removal is reasonable since while isopropyl alcohol is infinitely soluble in water, trichloroethylene is soluble only to the extent of 0.1% at 25° C. Pasteurization of chicken drumsticks was next attempted with condensing vapors from water boiling under reduced pressure in the range of 70 to 76°C. (Table
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inserted into one of the outer necks to measure the temperature of the boiling liquid. A tap water-cooled reflux condenser was attached to the other outer neck. For experiments at reduced pressure, the upper end of the condenser was connected to a mercury manometer and through a Cartesian manostat to a mechanical vacuum pump. About one kilogram of liquid was introduced into the flask, the heat input was adjusted to give vigorous boiling and refluxing of the liquid, short of flooding the condenser. Vapors of the boiling liquid were allowed to displace the air in the upper space of the flask before samples were introduced. In the use of water at reduced pressure, approximately two minutes were required to reduce the pressure in the flask to the value required for boiling in the 70 to 75°C. range. After the selected exposure to condensing liquid was completed, the drumstick was removed from the flask while suspended on a wire hook, the solvent was allowed to drain from the surface for one minute, and then the drumstick was placed in a plastic bag either for 3°C. storage, for frozen storage prior to tests for detection of residual liquids in the roasted meat, or for bacteriological assay as described above. There were from two to four replications of each pasteurizing condition within an experiment. For pasteurization of whole ready-to-cook fryers, a 5-gallon Pyrex reaction flask, equipped with a 5-neck hemispherical cover and heated by an electric mantle, was used, Reflux condenser, thermometer well, and suspension device were inserted in three of the necks.
508
A. A. KLOSE AND H. G. BAYNE TABLE 2.—Pasteurizing effect of condensing vapors from isopropyl alcohol boiling at 82°C. on chilled chicken drumsticks
Exposure to vapor (minutes)
none
Replications Average 3X105] 1X106 5X10* 1.2X10"J
Reduction factor for count
Shelf life at 3°C. Extension of shelf life over (days) 1 controls (days) Replications Average
1
—
—
0.5
9X102] 1.2X103 1.4X103 2.0X103J
4X102
1 >
1
1.4X102] 1.0X10H3X102 7.oxio2J
2X10S
!«>
2
lj}3
2X108
1J}»
12
22\ 2 2
16
3
J}1.5
3X106
4
2}<*
>SX106
2ir 2 23
1 2 2 I 2f "
6
10
16
Shelf life does not include 3-4 days from slaughter to retail market.
5). Almost complete elimination of surface bacteria was accomplished within 8 minutes and a substantial reduction (5 X
10s) within 4 minutes. All of the above results were obtained with drumsticks having the surface bac-
TABLE 3.—Pasteurizing effect of condensing vapors from trichloroethylene-water (condensing at 73^C.) on chilled chicken drumsticks Exposure to condensing vapor Total bacterial count per ml. of diluent (minutes)
Reduction factor for count
Extension of Shelf /life , at %3°C. shelf life over taaysj controls (days) Replications Average
Replications Average 1.8X106) 7X105 2.1X10* 1.6X10 3 5 1.1X10 6 3X10 2.1X10 6 4.3X10 6 1.7X10 5 1.1X104] 8.4X10 3 1X10 4 1.2X104J
30
2.0
2.3X105 9.4X10»\SX10, 1.7X10 8 / x
60
4.0
<10 7.5X10n6xl{)1 4.5X10 1 / x
5X10 3
^12 13/"
>3X10 4
17\19 21/ly
1.0
8.0
<101 <10 <10 <10j
n7 7/' 9/lu U
13
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1
Total bacterial count per ml. of diluent
509
POULTRY SURFACE PASTEURIZATION TABIJS 4.—Removal of organoleptically detectable traces of solvent from meat
Detection by odor triangle panel in freshly roasted meat Number of judgments: Correct/Total
Liquid-vapor treatment
Exposure (minute)
9 3 % Trichloroethylene' 7% Water 73°C.
1 2 4 8
Vacuum Vacuum Vacuum Vacuum
Isopropyl alcohol 82°C.
4 4 4
3°C. water soak-40 minutes 3°C. water soak-6 hours Warm air blast-1 minute plus 3°C. water soak-24 hours.
Method of removal
nonsignificant nonsignificant nonsignificant nonsignificant
16/18 significant 0 . 1 % 13/16 significant 0 . 1 % Solvent faintly detectable by single observer only. No panel evaluation.
the skin surface naturally rapidly acquires the temperature of the condensing liquid and the under surface approaches this temperature as the treatment continues. An illustration of this for the case of drumsticks treated with trichloroethylenewater condensing at 73°C. is given in Figure 2. Temperatures around and above 60°C. result in partial cooking of the outer layers; this would have an effect on flavor stability and the extent and significance of this cooking effect would have to be evaluated. These studies are of an exploratory na-
TABLE 5.—Pasteurizing effect of condensing vapors from water boiling at 76°C. on chilled chicken drumsticks , ^S°-SUre ^ " ™ S ^ 1r (minutes)
r
Total bacterial count per ml. of diluent Replications Average 2.6X10 5 ] SXlOHlXlOs 8X10^
Reduction factor for count
—
Shelf life at 3°C. (days)
?*f f en .?t 0n °L controls (days)
Replications Average 55) 7
L
—
7J 1.5X10 2 ! 1.3X104lXl02 2X10*J 5X10'1 4 2X10 1 2X10^
16
103
9/9
3
5X10 3
12\13 13/ 1 , s
7
17J 1 '
11
1 9 \ 1l y9 19f
13
?}1.5
7X10 4
°- 5 ^0 25
4X10 5
1 & pressure come-down time of 2 minutes was allowed before pressure required for 76°C. boiling point was reached and exposure time counted.
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terial contamination present in the retail packaged state. Additional tests on drumsticks and whole ready-to-cook fryers were carried out after inoculating the retail product with S. typhimurium as described under General Procedures. Results as summarized in Table 6 indicate substantial kills on drumsticks with isopropyl alcohol in 4 minutes, and 75°C. water in 8 minutes, with trichloroethyllene on whole fryers in 12 minutes, and a marginal reduction with trichloroethylene on drumsticks in 4 minutes. During the course of these treatments,
4/8 7/16 3/8 9/16
5 minutes 10 minutes 20 minutes 30 minutes
510
A. A, KLOSE AND H. G. BAYNK
Table 6.—Pasteurizing effect of condensing vapors on samples inoculated with Salmonella
Sample Drumsticks
Isopropyl alcohol B.P. 82°C.
Drumsticks
Water, B.P. 75°C.
Ready-to-cook fryer
— >10 2 >10*
•— —
3X10 5
— —
2X10
—2
10 SX10 2
6
—
— —
3X10 2 >2X10 5
— —
10
1.3X10*
—2
w
1
Samples dipped in inoculum containing 5 X10 6 S. typhimurium per ml., drained and held at 3°C. for one hour prior to pasteurization treatment.
ture. The overall reductions in bacteria are no doubt a summation of heating, rinsing, and bactericidal effects of the solvents; how much each effect contributes is not known. Potential advantages of the condensing vapor approach over a liquid dip at the same temperature include avoidance of a common bath, availability of the high latent heat of condensation given off at every point accessible to the vapors, and the possible greater penetrating power of the vapors into contaminated follicles and crevices in the outer and inner surface structure of the ready-to-cook carcass. Practical applications, in so far as organic solvents such as isopropyl alcohol or trichloroethylene are concerned, would first require complete evaluation of the hazards involved, both to the processing plant operator and to the consumer.
idly heating skin surfaces by the use of condensing vapors from boiling liquids. Chicken fryer drumsticks and whole fryers were used in small scale tests. Evaluation was based on reduction in bacterial numbers, shelf-life at 3°C. as indicated by absence of spoilage odor, and the completeness of removal of organic liquids as judged by odor of the meat after oven roasting to 85°C. Samples with natural flora and some inoculated with Salmonella typhimurium were studied. Acetone-water at 70°C. and isopropyl alcohol at 82°C. yielded 10,000- to
-
,,„,„»»»
60
"""'
^
^
^
^
"
UNDER SKIN
40
SUMMARY Bacterial food poisoning attributed to poultry has at times been traced to cross contamination between raw poultry surfaces and other foods not subsequently cooked. Since bactericidal agents such as chlorine solutions have proven inadequate for pasteurization, studies were made of the potential pasteurizing value of rap-
20
1
I
1
1
1
I
r
I
i
TIME (MINUTES)
FIG. 2. Temperature history of skin surface and point just under skin for drumstick exposed to 73°C. condensing vapors from trichloroethylene-water.
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Trichloroethylene-water (condensing at 73°C.)
Reduction factor for count
4X10 4
0 2 4 0 2 4 0 4 8 0 8 12
Trichloroethylene-water (condensing at 73°C.)
Drumsticks
Total bacterial count/ml. for controls
Exposure to vapor (minutes)
Type of condensing vapor
typhimurium1
POULTRY SURFACE PASTEURIZATION
REFERENCES Bryan, F. L., 1965. Factors associated with the dissemination of salmonellae in turkey products and processing plants. Thesis, Iowa State University of Science and Technology, Ames, Iowa.
Dawson, L. E., W. L. Mallmann, D. G. Bigbee, R. Walker and M. E. Zabik, 1963. Influence of surface pasteurization and chlorotetracycline on bacterial incidence on fryers. Food Technol. 17: 218-221. Sadler, W. W., and R. E. Corstvet, 1965. Second survey of market poultry for Salmonella infection. Appl. Microbiol. 13:348-351. Thomson, J. E., G. J. Barnwart, D. H. Sanders and A. J. Mercuri, 1967. Effect of chlorine, antibiotics, /3-propiolactone, acids, and washing on Salmonella typhimurium on eviscerated fryer chickens. Poultry Sci. 46: 146-151. Wabeck, C. J., D. V. Schwall, G. M. Evancho, J. G. Heck and A. B. Rogers, 1968. Salmonella and total count reduction in poultry treated with sodium hypochlorite solutions. Poultry Sci. 47; 1090-1094. Wilkinson, R. J., W. L. Mallmann, L. E. Dawson, T. F. Irmiter and J. A. Davidson, 1965. Effective heat processing for the destruction of pathogenic bacteria in turkey rolls. Poultry Sci. 44: 131-136. U.S. Department of Health, Education, and Welfare. Public Health Service, Bureau of Disease Prevention and Environmental Control, National Communicable Disease Center, Salmonella Surveillance Annual Summary, 1967.
Infectivity of Infectious Bursal Disease Virus for Embryonating Eggs S. B . HlTCHNER Department oj Avian Diseases, New York State Veterinary College, Cornell University, Ithaca, New York 14850 (Received for publication October 23, 1969)
T
HE disease that Cosgrove (1962) reported as avian nephrosis has since been referred to as infectious bursal disease. Early attempts to propagate the infectious bursal disease virus (IBDV) by serial passage in embryonating eggs frequently resulted in failure to maintain the virus. Landgraf et al. (1967) reported a typical experience that has been observed by other workers. Infective tissue suspensions killed all inoculated embryos on first passage. Materials from embryos of the first passage killed 30% of those in-
oculated on the second passage, and on the third passage there was no embryo mortality. In some of the initial studies with IBDV it was observed that eggs from certain supply flocks would not support the growth of the virus, suggesting that parental antibodies from immune dams may have inhibited the virus. However, this did not provide the full explanation for failures to maintain the virus since serial passage failed even when eggs from known susceptible flocks were used. The following
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100,000-fold bacterial reductions in 4minute exposures, but trace amounts of these liquids were difficult to remove from the cooked product. Trichloroethylenewater vapor at 73°C. and water under reduced pressure at 76° C. gave the same order of reduction after 8-minute exposures; trichloroethylene was less of a trace-removal problem than the other organic solvents. Shelf-life extensions over controls correlated roughly with bacterial reductions and exceeded 15 days in many cases. Practical applications would require complete evaluation of the acceptability and storage stability of the product, and of the potential hazards of any organic solvent used, both to processing plant operator and to the consumer.
511
A
Obvious avenues for control of salmonellae and other pathogens include 1) elimination of the microorganisms at one or more stages of production and processing, 2) inhibition of growth of existing low
levels of the microorganisms, and 3) destruction of the microorganisms on the final product. This paper is concerned with the last avenue mentioned, although this is not to discount the need and potential for implementing elimination of the microorganisms at their sources and inhibition of growth at all stages of utilization. We are further limiting our attention to surface pasteurization, because of the following considerations. Sterile conditions generally exist in the interior of poultry meat. Moreover, under normal cooking conditions, the interior of the meat should reach and exceed a temperature of 160°F., which should destroy salmonellae and eliminate any health hazards (Wilkinson et al., 1965). Finally the major hazard as we have noted and as documented by detailed U.S. Public Health reports of Salmonella food poisoning outbreaks, is cross-contamination between contaminated raw product and cooked products or products not requiring further cooking. Previously reported attempts to achieve surface pasteurization by dipping poultry in bactericidal solutions have met with little or no success. Wabeck et al. (1968) concluded, from extensive tests of sodium hypochlorite solutions on chicken drumsticks, that salmonellae inoculated at 100 cells per ml. on drumsticks were only reduced tenfold by constantly flowing 20 p.p.m. chlorine solutions. A 20 p.p.m. chlorine solution destroyed 1,000 salmonellae per ml. within 30 minutes when organic matter was absent, but available
504
Downloaded from http://ps.oxfordjournals.org/ at Oakland University on June 7, 2015
MONG the many animal derived food -products that have been implicated in Salmonella-caused food poisoning outbreaks, chicken and turkey meat have been involved in a substantial percentage of the cases. For example, in 1967, out of 25 outbreaks involving 5,600 people reported by the Salmonella Surveillance Reports, five outbreaks involving 2,295 people were traced to contaminated turkey meat. These cases arose mainly in institutional type feeding, so we may suspect that they might have been caused by poor handling practices in the institutional kitchens. However, the fact remains that poultry represents a widespread and ever present reservoir of salmonellae on the farm, in the processing plant (Bryan, 1965), and in the finished product (Sadler and Corstvet, 1965) as it moves to the point of consumption to be cooked. Since subjection of poultry meat products to an adequate end point cooking temperature will destroy all potential pathogenic microorganisms, it is reasonable to assume that the critical hazard lies in cross contamination between contaminated raw poultry, food handling surfaces, and food products that will not receive pathogenkilling heat treatment between contamination and consumption.
POULTRY SURFACE PASTEURIZATION
GENERAL EXPERIMENTAL PROCEDURES1 A major part of this research was carried out with commercial chicken fryer drumsticks. This raw material was fresh chilled, purchased from a retail market supplied by one processing plant, and 1 Reference to a company or product name does not imply approval or recommendation of the product by the U. S. Department of Agriculture to the exclusion of others that mav be suitable.
generally had consumed 2 to 4 days of its refrigerated shelf life when it was subjected to the pasteurization treatment. Treated and control drumsticks were held in individual polyethylene bags at 3°C. for determination of their remaining days of satisfactory refrigerated shelf life. End point was the time at which an incipient bacterial spoilage odor had developed in the meat. Development of fluorescence when exposed to ultraviolet radiation was also followed in all samples. Estimations of the number of viable microorganisms in the drumsticks and whole birds, initially and after the pasteurizing treatment, were determined in the following manner. Stock solution—Inocula. Two 250 ml. flasks containing 50 ml. of Trypticase Soy Broth and 2% Yeast Extract (TSB-YE) were inoculated with a culture of S. typhimurium Tm-1 (from a TSA-YE slant). The flasks were placed on a shaker in the 28°C. incubator and the culture allowed to grow for 48 hours. They were then removed, the contents decanted into small sterile centrifuge cups and centrifuged for 20 minutes at approximately 15,000 g. The broth was decanted and the cells were washed with sterile demineralized water; the process of centrifuging was done twice. The final cell pack was then suspended in 100 ml. of sterile demineralized water and stored in the refrigerator (5°C). The stock solution was found to contain 4.0 X10 9 cells per ml. Inoculation of drumsticks or birds with S. typhimurium Tm-1. 1.0 ml. of stock solution was diluted in 1,000 ml. sterile demineralized water to give a count of approximately 106. The birds or drumsticks were placed therein for 10 minutes, removed and allowed to drain. They were stored for one hour at 3°C. Counts were made of the inoculum by making serial dilutions in TSB-YE and spread-
Downloaded from http://ps.oxfordjournals.org/ at Oakland University on June 7, 2015
chlorine was rapidly depleted in the presence of poultry tissue. Sixty p.p.m. chlorine solution imparted an off-flavor and odor aftef a 4-hour application to thawing meat. Previously, Thomson et al. (1967) had also shown that sprays of chlorine solutions at 100 and 200 p.p.m. produced only small reduction in numbers of Salmonella typhimurium inoculated on chicken carcasses. Sprays of /3-propiolactone, succinic acid, and citric acid had only minor effects. Dawson et al. (1963) measured the extent of surface pasteurization of half chicken-fryers effected by slow agitation in water at temperatures ranging from 135°F. <57°C.) to 155°F. (68°C.) and for times from one to ten minutes. Total bacteria counts were reduced to 1/10-1/1,000 of control values; one to two log reductions with extensions of shelf life at 34°F. (1°C.) of about 4 days were accomplished in many cases. This paper describes several treatments that pasteurize poultry meat surfaces, all of which involve a condensation of distilling vapors from boiling liquid(s) onto the poultry meat surface for specified times. Relative effectiveness was estimated by determining reduction in bacterial numbers and extension of chilled shelf life. Studies included determination of ease of removal of residual solvents, and organoleptic acceptability of the cooked products.
505
506
A. A. K L O S E AND H. G. B A Y N E
plating 0.1 ml. aliquots in duplicate. Plates were incubated at 28°C. for 24 or more hours, removed and counted. Sampling controls and treated birds or drumsticks. (A). Control and treated birds were covered with 500 ml. sterile demineralized water in Cryovac bags and allowed to stand for 5 to 10 minutes with severe intermittent agitation. 1.0 ml. of this new suspension was then serially diluted and 0.1 ml. aliquots of each dilution in duplicate were plated onto T S A - Y E and BGA (Brilliant Green Agar), spread, incubated a t 28°C. a n d counted. 0.5 ml. aliquots of the undiluted suspensions were also used. (B). Drumsticks, of 80-100 grams weight, were placed in whirlbags and covered with 100 ml. or (later) 25 ml.
T S B - Y E . The resulting agitated suspensions were diluted and plated as described for the whole birds, except t h a t 0.5 ml. or 1.0 ml aliquots of the undiluted suspensions were plated directly. Drumsticks were pasteurized b y condensing vapors from solvents introduced into a 12-liter, round bottomed, 3-neck Pyrex flask, heated on its lower surface by the lower heating element of a 2-element hemispherical electrical heating mantle controlled through a variable voltage transformer (Figure 1). T h e central neck was used interchangeably, either to insert a thermometer to record the condensing temperature of the liquid system, or to introduce and suspend the drumstick b y a wire hook in the vapor phase above the boiling liquid. A thermometer well was
Downloaded from http://ps.oxfordjournals.org/ at Oakland University on June 7, 2015
FIG. 1. Flask used for pasteurization of drumsticks.
507
POULTRY SURFACE PASTEURIZATION
RESULTS AND DISCUSSION
The first liquids tested were mixtures of acetone and water, which produced substantial reductions in total bacterial count and extensions of chilled shelf life (Table 1). The use of acetone was not considered
TABLE 1.—Pasteurizing effect of condensing vapors (70°C.) from 25% acetone—75% water solution on chicken drumsticks Exposure to Total bacterial Shelf life at 3 ° C , condensing vapor count per ml. beyond exposure (minutes) of diluent (days) 0 0 S 10
8X10 7 1X10 8 6X10 3 6X10 1
<4 <4 15 21
promising, however, because of the extreme difficulty of removing the last organoleptically detectable trace of the solvent from the meat. Tests of isopropyl alcohol on drumsticks resulted in almost complete elimination of surface bacterial contamination within 4 minutes, and 16 days extension of shelf life (Table 2). An azeotropic mixture of trichloroethylene and water (Table 3) condensing at a much lower temperature (73°C.) than isopropyl alcohol, gave substantial bacterial kills within 4 to 8 minutes. Attempts to remove the last organoleptically detectable traces of these solvents from the drumsticks met with only limited success (Table 4). Soaking the drumsticks treated with isopropyl alcohol for 4 minutes in 3°C. water for as long as 6 hours left definite traces of isopropyl alcohol odor in the freshly roasted drumsticks, and even 24 hours' soaking left a faint trace. Vacuum treatment of trichloroethylene samples reduced the solvent level to a point where an odor panel was unable to distinguish solvent treated samples from controls in triangle comparisons. This difference in ease of removal is reasonable since while isopropyl alcohol is infinitely soluble in water, trichloroethylene is soluble only to the extent of 0.1% at 25° C. Pasteurization of chicken drumsticks was next attempted with condensing vapors from water boiling under reduced pressure in the range of 70 to 76°C. (Table
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inserted into one of the outer necks to measure the temperature of the boiling liquid. A tap water-cooled reflux condenser was attached to the other outer neck. For experiments at reduced pressure, the upper end of the condenser was connected to a mercury manometer and through a Cartesian manostat to a mechanical vacuum pump. About one kilogram of liquid was introduced into the flask, the heat input was adjusted to give vigorous boiling and refluxing of the liquid, short of flooding the condenser. Vapors of the boiling liquid were allowed to displace the air in the upper space of the flask before samples were introduced. In the use of water at reduced pressure, approximately two minutes were required to reduce the pressure in the flask to the value required for boiling in the 70 to 75°C. range. After the selected exposure to condensing liquid was completed, the drumstick was removed from the flask while suspended on a wire hook, the solvent was allowed to drain from the surface for one minute, and then the drumstick was placed in a plastic bag either for 3°C. storage, for frozen storage prior to tests for detection of residual liquids in the roasted meat, or for bacteriological assay as described above. There were from two to four replications of each pasteurizing condition within an experiment. For pasteurization of whole ready-to-cook fryers, a 5-gallon Pyrex reaction flask, equipped with a 5-neck hemispherical cover and heated by an electric mantle, was used, Reflux condenser, thermometer well, and suspension device were inserted in three of the necks.
508
A. A. KLOSE AND H. G. BAYNE TABLE 2.—Pasteurizing effect of condensing vapors from isopropyl alcohol boiling at 82°C. on chilled chicken drumsticks
Exposure to vapor (minutes)
none
Replications Average 3X105] 1X106 5X10* 1.2X10"J
Reduction factor for count
Shelf life at 3°C. Extension of shelf life over (days) 1 controls (days) Replications Average
1
—
—
0.5
9X102] 1.2X103 1.4X103 2.0X103J
4X102
1 >
1
1.4X102] 1.0X10H3X102 7.oxio2J
2X10S
!«>
2
lj}3
2X108
1J}»
12
22\ 2 2
16
3
J}1.5
3X106
4
2}<*
>SX106
2ir 2 23
1 2 2 I 2f "
6
10
16
Shelf life does not include 3-4 days from slaughter to retail market.
5). Almost complete elimination of surface bacteria was accomplished within 8 minutes and a substantial reduction (5 X
10s) within 4 minutes. All of the above results were obtained with drumsticks having the surface bac-
TABLE 3.—Pasteurizing effect of condensing vapors from trichloroethylene-water (condensing at 73^C.) on chilled chicken drumsticks Exposure to condensing vapor Total bacterial count per ml. of diluent (minutes)
Reduction factor for count
Extension of Shelf /life , at %3°C. shelf life over taaysj controls (days) Replications Average
Replications Average 1.8X106) 7X105 2.1X10* 1.6X10 3 5 1.1X10 6 3X10 2.1X10 6 4.3X10 6 1.7X10 5 1.1X104] 8.4X10 3 1X10 4 1.2X104J
30
2.0
2.3X105 9.4X10»\SX10, 1.7X10 8 / x
60
4.0
<10 7.5X10n6xl{)1 4.5X10 1 / x
5X10 3
^12 13/"
>3X10 4
17\19 21/ly
1.0
8.0
<101 <10 <10 <10j
n7 7/' 9/lu U
13
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1
Total bacterial count per ml. of diluent
509
POULTRY SURFACE PASTEURIZATION TABIJS 4.—Removal of organoleptically detectable traces of solvent from meat
Detection by odor triangle panel in freshly roasted meat Number of judgments: Correct/Total
Liquid-vapor treatment
Exposure (minute)
9 3 % Trichloroethylene' 7% Water 73°C.
1 2 4 8
Vacuum Vacuum Vacuum Vacuum
Isopropyl alcohol 82°C.
4 4 4
3°C. water soak-40 minutes 3°C. water soak-6 hours Warm air blast-1 minute plus 3°C. water soak-24 hours.
Method of removal
nonsignificant nonsignificant nonsignificant nonsignificant
16/18 significant 0 . 1 % 13/16 significant 0 . 1 % Solvent faintly detectable by single observer only. No panel evaluation.
the skin surface naturally rapidly acquires the temperature of the condensing liquid and the under surface approaches this temperature as the treatment continues. An illustration of this for the case of drumsticks treated with trichloroethylenewater condensing at 73°C. is given in Figure 2. Temperatures around and above 60°C. result in partial cooking of the outer layers; this would have an effect on flavor stability and the extent and significance of this cooking effect would have to be evaluated. These studies are of an exploratory na-
TABLE 5.—Pasteurizing effect of condensing vapors from water boiling at 76°C. on chilled chicken drumsticks , ^S°-SUre ^ " ™ S ^ 1r (minutes)
r
Total bacterial count per ml. of diluent Replications Average 2.6X10 5 ] SXlOHlXlOs 8X10^
Reduction factor for count
—
Shelf life at 3°C. (days)
?*f f en .?t 0n °L controls (days)
Replications Average 55) 7
L
—
7J 1.5X10 2 ! 1.3X104lXl02 2X10*J 5X10'1 4 2X10 1 2X10^
16
103
9/9
3
5X10 3
12\13 13/ 1 , s
7
17J 1 '
11
1 9 \ 1l y9 19f
13
?}1.5
7X10 4
°- 5 ^0 25
4X10 5
1 & pressure come-down time of 2 minutes was allowed before pressure required for 76°C. boiling point was reached and exposure time counted.
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terial contamination present in the retail packaged state. Additional tests on drumsticks and whole ready-to-cook fryers were carried out after inoculating the retail product with S. typhimurium as described under General Procedures. Results as summarized in Table 6 indicate substantial kills on drumsticks with isopropyl alcohol in 4 minutes, and 75°C. water in 8 minutes, with trichloroethyllene on whole fryers in 12 minutes, and a marginal reduction with trichloroethylene on drumsticks in 4 minutes. During the course of these treatments,
4/8 7/16 3/8 9/16
5 minutes 10 minutes 20 minutes 30 minutes
510
A. A, KLOSE AND H. G. BAYNK
Table 6.—Pasteurizing effect of condensing vapors on samples inoculated with Salmonella
Sample Drumsticks
Isopropyl alcohol B.P. 82°C.
Drumsticks
Water, B.P. 75°C.
Ready-to-cook fryer
— >10 2 >10*
•— —
3X10 5
— —
2X10
—2
10 SX10 2
6
—
— —
3X10 2 >2X10 5
— —
10
1.3X10*
—2
w
1
Samples dipped in inoculum containing 5 X10 6 S. typhimurium per ml., drained and held at 3°C. for one hour prior to pasteurization treatment.
ture. The overall reductions in bacteria are no doubt a summation of heating, rinsing, and bactericidal effects of the solvents; how much each effect contributes is not known. Potential advantages of the condensing vapor approach over a liquid dip at the same temperature include avoidance of a common bath, availability of the high latent heat of condensation given off at every point accessible to the vapors, and the possible greater penetrating power of the vapors into contaminated follicles and crevices in the outer and inner surface structure of the ready-to-cook carcass. Practical applications, in so far as organic solvents such as isopropyl alcohol or trichloroethylene are concerned, would first require complete evaluation of the hazards involved, both to the processing plant operator and to the consumer.
idly heating skin surfaces by the use of condensing vapors from boiling liquids. Chicken fryer drumsticks and whole fryers were used in small scale tests. Evaluation was based on reduction in bacterial numbers, shelf-life at 3°C. as indicated by absence of spoilage odor, and the completeness of removal of organic liquids as judged by odor of the meat after oven roasting to 85°C. Samples with natural flora and some inoculated with Salmonella typhimurium were studied. Acetone-water at 70°C. and isopropyl alcohol at 82°C. yielded 10,000- to
-
,,„,„»»»
60
"""'
^
^
^
^
"
UNDER SKIN
40
SUMMARY Bacterial food poisoning attributed to poultry has at times been traced to cross contamination between raw poultry surfaces and other foods not subsequently cooked. Since bactericidal agents such as chlorine solutions have proven inadequate for pasteurization, studies were made of the potential pasteurizing value of rap-
20
1
I
1
1
1
I
r
I
i
TIME (MINUTES)
FIG. 2. Temperature history of skin surface and point just under skin for drumstick exposed to 73°C. condensing vapors from trichloroethylene-water.
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Trichloroethylene-water (condensing at 73°C.)
Reduction factor for count
4X10 4
0 2 4 0 2 4 0 4 8 0 8 12
Trichloroethylene-water (condensing at 73°C.)
Drumsticks
Total bacterial count/ml. for controls
Exposure to vapor (minutes)
Type of condensing vapor
typhimurium1
POULTRY SURFACE PASTEURIZATION
REFERENCES Bryan, F. L., 1965. Factors associated with the dissemination of salmonellae in turkey products and processing plants. Thesis, Iowa State University of Science and Technology, Ames, Iowa.
Dawson, L. E., W. L. Mallmann, D. G. Bigbee, R. Walker and M. E. Zabik, 1963. Influence of surface pasteurization and chlorotetracycline on bacterial incidence on fryers. Food Technol. 17: 218-221. Sadler, W. W., and R. E. Corstvet, 1965. Second survey of market poultry for Salmonella infection. Appl. Microbiol. 13:348-351. Thomson, J. E., G. J. Barnwart, D. H. Sanders and A. J. Mercuri, 1967. Effect of chlorine, antibiotics, /3-propiolactone, acids, and washing on Salmonella typhimurium on eviscerated fryer chickens. Poultry Sci. 46: 146-151. Wabeck, C. J., D. V. Schwall, G. M. Evancho, J. G. Heck and A. B. Rogers, 1968. Salmonella and total count reduction in poultry treated with sodium hypochlorite solutions. Poultry Sci. 47; 1090-1094. Wilkinson, R. J., W. L. Mallmann, L. E. Dawson, T. F. Irmiter and J. A. Davidson, 1965. Effective heat processing for the destruction of pathogenic bacteria in turkey rolls. Poultry Sci. 44: 131-136. U.S. Department of Health, Education, and Welfare. Public Health Service, Bureau of Disease Prevention and Environmental Control, National Communicable Disease Center, Salmonella Surveillance Annual Summary, 1967.
Infectivity of Infectious Bursal Disease Virus for Embryonating Eggs S. B . HlTCHNER Department oj Avian Diseases, New York State Veterinary College, Cornell University, Ithaca, New York 14850 (Received for publication October 23, 1969)
T
HE disease that Cosgrove (1962) reported as avian nephrosis has since been referred to as infectious bursal disease. Early attempts to propagate the infectious bursal disease virus (IBDV) by serial passage in embryonating eggs frequently resulted in failure to maintain the virus. Landgraf et al. (1967) reported a typical experience that has been observed by other workers. Infective tissue suspensions killed all inoculated embryos on first passage. Materials from embryos of the first passage killed 30% of those in-
oculated on the second passage, and on the third passage there was no embryo mortality. In some of the initial studies with IBDV it was observed that eggs from certain supply flocks would not support the growth of the virus, suggesting that parental antibodies from immune dams may have inhibited the virus. However, this did not provide the full explanation for failures to maintain the virus since serial passage failed even when eggs from known susceptible flocks were used. The following
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100,000-fold bacterial reductions in 4minute exposures, but trace amounts of these liquids were difficult to remove from the cooked product. Trichloroethylenewater vapor at 73°C. and water under reduced pressure at 76° C. gave the same order of reduction after 8-minute exposures; trichloroethylene was less of a trace-removal problem than the other organic solvents. Shelf-life extensions over controls correlated roughly with bacterial reductions and exceeded 15 days in many cases. Practical applications would require complete evaluation of the acceptability and storage stability of the product, and of the potential hazards of any organic solvent used, both to processing plant operator and to the consumer.
511