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Effect of the Steam Conditioning and Pelleting Process on the Microbiology and Quality of Commercial-Type Poultry Feeds
Effect of the Steam Conditioning and Pelleting Process on the Microbiology and Quality of Commercial-Type Poultry Feeds N. A. COX, D. BURDICK, J. S. BAILEY, and J. E. THOMSON USDA, ARS, Richard B. Russell Agricultural Research Center P.O. Box 5677, Athens, Georgia 30613 (Received for publication July 8, 1985)
1986 Poultry Science 65:704-709
INTRODUCTION In t h e 1950's animal feed was first recognized as a possible source of Salmonella ultim a t e l y affecting t h e h u m a n food supply. Animals (such as p o u l t r y ) could c o n s u m e feed c o n t a m i n a t e d with Salmonella, t h e n could b e c o m e infected with Salmonella, often w i t h o u t exhibiting clinical s y m p t o m s . C o n t a m i n a tion of t h e processing facilities resulted w h e n these animals were processed, and significant n u m b e r s of initially u n c o n t a m i n a t e d carcasses were c o n t a m i n a t e d b y c o n t a c t with e q u i p m e n t a n d o t h e r carcasses in normal processing. This has been d e m o n s t r a t e d b y investigators w h o f o u n d the same serotypes of Salmonella on p o u l t r y farms a n d feed t h a t were also f o u n d o n t h e broiler carcasses from t h e processing plant (MacKenzie and Bains, 1 9 7 6 ; Voeten et al, 1974). Erwin ( 1 9 5 5 ) was t h e first t o recover viable Salmonella from commercial p o u l t r y feed. O t h e r studies since have s h o w n t h a t t h e percentage of p o u l t r y mash samples c o n t a m i n a t e d with Salmonella organisms were 4% (Isa et al, 1963), 5% (Morehouse and W e d m a n , 1 9 6 1 ; Allred et al, 1967), 9% (Hobbs, 1 9 6 1 ) , 2 1 . 5 % (Morris et al, 1 9 6 9 ) , 4 3 . 5 % (MacKenzie a n d Bains, 1976), a n d 6 8 % (Cox et al, 1983). It is u n k n o w n w h e t h e r t h e higher percentages en-
c o u n t e r e d in m o r e recent studies reflected a true worsening of t h e problem o r resulted from i m p r o v e m e n t s in microbiological m e t h o d o l o g y for recovering Salmonella from feeds. Percentages of pelleted p o u l t r y feed f o u n d t o b e cont a m i n a t e d w i t h Salmonella were .7% (Allred et al, 1 9 6 7 ) , 1.7% (Hobbs, 1 9 6 1 ) , 4 . 3 % (Hacking et al, 1 9 7 8 ) , and 2 3 % (Cox et al, 1983). T h e objectives of this s t u d y were t o determine t h e effect of steam conditioning and pelleting of t w o types of p o u l t r y feed [broilerstarter (BS) a n d layer-breeder (LB)] on 1) t h e presence of Salmonella, n u m b e r s of Enterobacteriaceae, total n u m b e r s of bacteria and moisture at various locations in a commercial feed mill; 2) t h e t e m p e r a t u r e of t h e feed after t h e conditioning-pelleting process; and 3) t h e durability of t h e pellets. A small scale commercial feed mill, in which steam pressures for conditioning and feed types could be altered, was used in this s t u d y .
MATERIALS AND METHODS In a small scale commercial-type feed mill (University of Georgia) t w o types of p o u l t r y feed (BS a n d LB) were c o n d i t i o n e d at four different steam pressures [low (100 lb/hr); m e d i u m ( 2 0 0 l b / h r ) ; and high (300 lb/hr), t h e n
704
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ABSTRACT Effects of variations in steam conditioning and pelleting poultry feed to eliminate Salmonella were investigated in a commercial pellet mill. Layer-breeder and broiler-starter rations differing primarily in fat and limestone content were evaluated. Total bacteria counts were reduced only slightly, but Enterobacteriaceae counts were reduced appreciably by steam conditioning; however, pelleting was also necessary to eliminate Enterobacteriaceae consistently. Salmonella were present in about 50% of the feed samples before conditioning and in only about 4% of all samples after conditioning and pelleting. No Salmonella was detected after pelleting with high or very high steam pressure conditioning. Moisture content of the feed remained in an acceptable range regardless of steam pressure used. Temperature of the feed following the conditioning process was 134 to 135 F (57 C), 162 to 169 F (72 to 76 C), and 181 to 187 F (83 to 86 C) with low, medium, and high steam, respectively. The layer-breeder pellets were slightly more durable than the broiler-starter pellets, and overall pellet durability increased with increasing steam pressure. (Key words.- steam, pelleting, Salmonella, Enterobacteriaceae, temperature, feed)
STEAM, PELLETING ON POULTRY FEED
Model 8693-2 indicating Thermocouple Potentiometer equipped with a No. 30 Brown and Sharpe gauge duplex copper-constantan thermocouple. Feed (200 g) was collected in an insulated container; then thermocouples were immediately thrust into three different locations in the feed near the center of the container, and values were averaged. Pellet Durability Determination. The standard method for pellet durability of the American Society of Agricultural Engineers (ASAE, 1982) was used. Samples of whole pellets (500 g) were tumbled in a box for 10 min at 50 rpm, then screened. Pellet durability was expressed as the percentage of whole pellets recovered. This was replicated three times for both feed types and for low, medium, and high steam pressures. Statistical analysis of TPC and ENT were run with the general linear models procedure (SAS, 1985) using preplanned single degree of freedom contrasts to compare TPC and ENT before conditioning with each of the other three conditions. RESULTS AND DISCUSSION
Microbiology. The range of TPC before conditioning was small, only log 10 4.7 to 5.2 (Table 1). Small changes in TPC were observed as a result of the conditioning-pelleting process. The conditioning-pelleting operation is not intended to sterilize the feed; many microorganisms present in the feed, such as gram-positive sporeforming rods, and gram-positive cocci are more resistant to heat than Salmonella or other Enterobacteriaceae. The TPC per gram in the feed was generally logio 4 to 5 after conditioning and pelleting. Furuta et al. (1980) reported logio 4.5 total bacteria/g of mash and logio 1.1 total bacteria/g of pellets. Also, Cover et al. (1984) reported total bacteria counts similar to ours after conditioning and pelleting. We observed a slight increase in average TPC after cooling of the pellets. This may have been the result of blowing air from within the mill over the pellets to cool them. Riley (1969) reported a count of 20 to 200 microorganisms/ft 3 in a dusty feed mill. The ENT of feeds before conditioning ranged from logio 3.5 to 4.3 (Table 2). After conditioning with either low or medium steam pressure, there was little or no reduction of ENT. After high steam pressure conditioning, ENT were reduced to approximately logio 2.0.
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pelleted in a 40-hp California pellet mill with a 6.8-cm (2-2/3 in) die. Samples for microbiological analyses were aseptically taken before conditioning, after conditioning, after pelleting, and after cooling of the pellets. Separate samples were also taken to determine moisture levels, temperature of the feed after conditioning and pelleting, and durability of the pellets. Microbiological Analyses. Fifty grams of each sample were placed in a sterile screw cap jar with 450 ml of sterile buffered peptone (.1%) and vigorously shaken for 1 min. Serial dilutions were made and a total aerobic plate count (TPC) and an Enterobacteriaceae count (ENT) were run from the diluted sample. The pour plate technique with plate count agar (Difco) was used for the TPC and the plates were incubated at 35 to 37 C for 48 hr. From the same diluted samples, an ENT was determined [violet red bile with 1% glucose agar (Mossel et al, 1962)] with the pour plate technique plus an overlay. These plates were incubated at 3 5 C for 24 hr. For Salmonella determination, 50 g of feed were placed in a sterile container with 450 ml of sterile 1% buffered peptone (Juven et al., 1984), agitated for 30 sec with a sterile pipette, and incubated for 24 hr at 35 C. One milliliter was then aseptically transferred to tubes containing 10 ml of tetrathionate broth. These tubes were also incubated 24 hr at 35 C and then were streaked for isolation onto three selective plating media: BG sulfa, bismuth sulfite, and modified lysine iron agar (Rappold and Bolderdijk, 1979). After 24 hr at 35 C, two colonies with characteristics typical of Salmonella were selected from each plate and inoculated into lysine iron agar slants. Slants exhibiting a typical Salmonella reaction after 24 hr incubation at 35 C were streaked to determine purity and to produce isolated colonies on brain-heart infusion agar. Following 24 hr incubation at 35 C, the pure cultures were biochemically tested with Micro-ID (General Diagnostics, Morris Plains, NJ) and serologically tested with Poly O and H antisera to confirm the presence of Salmonella. Moisture Determination. Samples for moisture determination were taken at the same locations as the microbiological samples. Moisture was determined by drying duplicate 2-g samples in a forced draft oven (130 C) for 2 hr, averaging, then calculating weight loss. Temperature Determination. Temperature was measured with a Leeds and Northrup
705
4.4 a
4.5a
4.9 a
Mean
4.9 a 4.5a 4.3a 4.7 a
Mean
1.9a
2.7 D
3.0 b
Mean
1
3.5 1.7 0 2.4
3.7 3.4 1.1 2.7
3.7' 3.7 2.0 2.7
Before conditioner After conditioner After pelleter After cooling
4.3 4.5 0 2.3
3.6C 2.?bc 1.0a 2.6 b
Counts expressed as logarithms (base 10) of number per gram of feed.
2.8 a
Low
Mean
Conditioning steam pressure
' ' c Means within a column or row with different superscripts are significantly different (P = .05).
High
Medium
Low
Broiler-starter
TABLE 2. Enterobacteriaceae counts in broiler-starter and layer-breeder feed in a comme with low, medium, and high steam pressure conditioning
Counts expressed as logarithms (base 10) of number per gram of feed.
Sampling location
1
4.8 a
5.2 5.0 4.7 4.3
Low
Conditioning steam pressure
a ' b Means within a column or row with different superscripts are significantly different (P = .05). i
5.0 4.0 3.8 4.6
4.7 4.8 4.2 4.4
4.8 1 4.8 4.7 5.0
Before conditioner After conditioner After pelleter After cooling
High
Medium
Low
Sampling location
Broiler-starter
TABLE 1. Total plate count in broiler-starter and layer-breeder feed in a commerci with low, medium, and high steam pressure conditioning
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STEAM, PELLETING ON POULTRY FEED
Seven of the 12 samples of LB were positive for Salmonella before conditioning, but Salmonella were not detected in any samples after conditioning, pelleting, or cooling (Table 3). Five of the 12 samples of BS were positive for Salmonella before conditioning, and 1 was positive after conditioning, 1 after pelleting, but none after cooling. Cover et al. (1984) reported similar results in that they encountered an occasional Salmonella-positive sample after conditioning and pelleting. Conditioning with the high steam pressure appeared to give the best results; no Salmonella nor ENT was detected in
TABLE 3. Salmonella in broiler-starter and layer-breeder feed in a commercial feed pelleting mill with low, medium, and high steam pressure conditioning Before conditioner
After conditioner
After pelleter
After cooling
Type of feed
Steam pressure
Broiler-starter
Low
1/41
Medium High
3/4 1/4
1/4 0/4 0/4
0/4 1/4 0/4
0/4 0/4 0/4
5/12
1/12
1/12
0/12
4/4 3/4 0/4
0/4 0/4 0/4
0/4 0/4 0/4
0/4 0/4 0/4
7/12
0/12
0/12
0/12
12/24
1/24
1/24
0/24
Layer-breeder
Low
Medium High Total 1
Number of positive samples/number of samples tested.
TABLE 4. Moisture content (%) of broiler-starter and layer-breeder feed in a commercial feed pelleting mill with low, medium, and high steam pressure conditioning Steam pressure
Sampling location
Broilerstarter
Layerbreeder
Low
Before conditioner After conditioner After pelleter After cooling
12.1 13.2 13.1 11.6
11.6 13.2 13.5 11.9
Medium
Before conditioner After conditioner After pelleter After cooling
11.8 13.5 13.5 11.9
11.6 13.9 13.7 11.9
High
Before conditioner After conditioner After pelleter After cooling
11.9 15.5 14.9 12.8
11.7 13.9 14.1 11.9
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After pelleting, no ENT were found in any of the LB samples regardless of steam pressure. However, ENT were found in BS feed after low and medium but not after high steam pressure conditioning. Differences between BS and LB may have been caused by the higher fat content and thus greater lubricity of BS in the pelleter diet. The LB feed was also higher in limestone, which may have increased friction in the die, thereby increasing temperature. We found ENT in all samples of pellets after cooling; ENT were probably from recontamination by the feed mill equipment and environment.
COX ET AL.
708
any of t h e samples following t h e conditioningpelleting process. A very high s t e a m pressure ( 3 5 0 l b / h r ) conditioning was also tried. N o Salmonella o r E N T was d e t e c t e d in any of t h e samples following conditioning or t h e conditioning-pelleting process; however, t h e pellet mill did n o t o p e r a t e efficiently at this pressure. Within 5 t o 10 min at very high steam pressure, t h e pellet mill would b e c o m e clogged and would n o longer properly pellet t h e feed. Therefore this s t e a m pressure was n o t studied further.
TABLE 5. Temperature of broiler-starter and layer-breeder feed after the conditioner-pelleting process in a commercial feed pelleting mill with low, medium, and high steam pressure conditioning Type of feed Steam pressure
Broilerstarter
Low Medium High
57 72 83
Layerbreeder (°C) 57 77 87
1 Average temperature determinations made at three different locations in the feed sample.
Replication 2 3
Type of feed
Steam pressure
1
Broiler-starter
Low Medium High
52 1 54 60
56 56 62
56 56 63
Layer-breeder
Low Medium High
64 71 77
66 72 79
66 72 78
1
Percent of whole pellets recovered.
ACKNOWLEDGMENTS We t h a n k Mike Ban, Marty French, and Debbie Posey for their very able technical assistance and J o y Cornelius and Sandra Willis for their very able clerical assistance. M e n t i o n of specific b r a n d names does n o t imply e n d o r s e m e n t b y t h e authors or institut i o n s a t w h i c h t h e y are e m p l o y e d t o t h e exclusion of o t h e r p r o d u c t s n o t m e n t i o n e d .
REFERENCES AUred, J. N., J. W. Walker, V. C. Beal, Jr., and F. W. Germaine, 1967. A survey to determine the salmonella contamination rate in livestock and poultry feeds. J. Am. Vet. Med. Assoc. 151: 1857-1860. American Society of Agricultural Engineers, 1982. ASAE Yearbook 1982-1983. ASAE S 269.3. Cover, M. S., J. T. Gary, and S. F. Binder, 1984. Reduction of standard plate counts, total coliform counts and Salmonella by pelletizing animal feed. Pages 221-231 in Proc. Int. Symp. Salmonella, New Orleans, LA. Cox, N. A., J. S. Bailey, and J. E. Thomson, 1983. Comparison of preenrichment to direct enrichment and the effect of pyruvate in media for recovery of salmonellae in feed. Poultry Sci. 62: 947-951. Erwin, L. E., 1955. Examination of prepared poultry feeds for the presence of Salmonella and other enteric organisms. Poultry Sci. 34:215—216. Furuta, K., I. Oku, and S. Morimoto, 1980. Effect of steam temperature in the pelleting process of chicken food on the viability of contaminating bacteria. Lab. Anim. 14:293-296. Hacking, W. C , W. R. Mitchell, and H. C. Carlson, 1978. Salmonella investigation in an Ontario feed mill. Can. J. Comp. Med. 42:400-406. Hobbs, B. C , 1961. Public health significance of Salmonella carriers in livestock and birds. J. Appl. Bacteriol. 24:340-352.
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Moisture. T h e values for moisture of t h e feed r e m a i n e d in an acceptable range regardless of steam pressure (Table 4 ) . Temperature. Feed after t h e conditioningpelleting process was 134 t o 135 F (57 C) with low steam pressure, 162 F (72 t o 76 C) with m e d i u m , and 1 8 1 t o 1 8 7 F (83 t o 8 6 C) w i t h high (Table 5). Mossel et al. ( 1 9 6 7 ) r e p o r t e d a 1 0 3 r e d u c t i o n of ENT in feed pelleted at 51 t o 6 7 C a n d a 1 0 5 r e d u c t i o n at 8 0 t o 83 C. S t o t t et al. ( 1 9 7 5 ) f o u n d a 10 2 to 1 0 3 r e d u c t i o n of ENT/g of feed after heating t o 63 t o 85 C, and coliforms were eliminated from feed w h e n pelleting was performed at over 8 0 C ( F u r u t a et al, 1 9 8 0 ) . Tellet Durability. Durability of t h e pellets was superior at higher steam pressures and LB pellets were m o r e durable t h a n BS pellets, possibly because of a lower percentage of fat in t h e LB pullets (Table 6 ) . F u r t h e r investigations are u n d e r w a y t o d e t e r m i n e t h e effect of pelleting rate and size of openings in t h e die o n survival of Salmonella and o t h e r E N T in various types of p o u l t r y feed.
TABLE 6. Average durability of pellets from broiler-starter and layer-breeder feed obtained from a commercial feed pelleting mill with low, medium, and high steam pressure conditioning
STEAM, PELLETING ON POULTRY FEED
dium for the selective growth and enumeration of Enterobacteriaceae. J. Bacteriol. 84:381. Mossel, D.A.A., M. van Schothorst, and E. H. Kampelmacher, 1967. Comparative study on decontamination of mixed feeds by radicidation and by pelletization. J. Sci. Food Agric. 18:362. Rappold, H., and R. F. Bolderdijk, 1979. Modified lysine iron agar for isolation of Salmonella from food. Appl. Environ. Microbiol. 38:162—163. Riley, P. B., 1969. Salmonella infection: the position of animal food and its manufacturing process. Page 101 in Bacterial Food Poisoning. J. Taylor, ed. R. Soc. Health, London. SAS Institute, Inc., 1985. SAS User's Guide: Statistics. 5th ed. Cary, NC. Stott, J. A„ J. E. Hodgson, and J. C. Chaney, 1975. Incidence of salmonellae in animal feed and the effect of pelleting on content of Enterobacteriaceae. J. Appl. Bacteriol. 39:41-46. Voeten, A. C , D.H.J. Brus, and F.H.J. Jaartsveld, 1974. Distribution of Salmonella within a closed broiler chicken operation. Tydsk. Diergeneeskd. 99:1093-1094.
Downloaded from http://ps.oxfordjournals.org/ at Florida Atlantic University on November 13, 2014
Isa, J. M., B. R. Boycott, and E. Broughton, 1963. A survey of Salmonella contamination in animal feed and feed constituents. Can. Vet. J. 11:41 — 43. Juven, B. J„ N. A. Cox, J. S. Bailey, J. E. Thomson, O. W. Charles, and J. V. Schutze, 1984. Recovery of Salmonella from artificially contaminated poultry feeds in nonselective and selective broth media. J. Food Prot. 47:299-302. MacKenzie, M. A., and B. S. Bains, 1976. Dissemination of Salmonella serotypes from raw feed ingredients to chicken carcasses. Poultry Sci. 55:957— 960. Morehouse, L. G., and E. E. Wedman, 1961. Salmonella and other disease-producing organisms in animal by-products—a survey. J. Am. Vet. Med. Assoc. 139:989-995. Morris, G. K., B. L. McMurray, M. M. Galton, and J. G. Wells, 1969. A study of the dissemination of salmonellosis in a commercial broiler chicken operation. Am. J. Vet. Res. 30:1413-1421. Mossel, D.A.A., W.H.J. Mengerink, and H. H. Schotts, 1962. Use of a modified MacConkey agar me-
709
1986 Poultry Science 65:704-709
INTRODUCTION In t h e 1950's animal feed was first recognized as a possible source of Salmonella ultim a t e l y affecting t h e h u m a n food supply. Animals (such as p o u l t r y ) could c o n s u m e feed c o n t a m i n a t e d with Salmonella, t h e n could b e c o m e infected with Salmonella, often w i t h o u t exhibiting clinical s y m p t o m s . C o n t a m i n a tion of t h e processing facilities resulted w h e n these animals were processed, and significant n u m b e r s of initially u n c o n t a m i n a t e d carcasses were c o n t a m i n a t e d b y c o n t a c t with e q u i p m e n t a n d o t h e r carcasses in normal processing. This has been d e m o n s t r a t e d b y investigators w h o f o u n d the same serotypes of Salmonella on p o u l t r y farms a n d feed t h a t were also f o u n d o n t h e broiler carcasses from t h e processing plant (MacKenzie and Bains, 1 9 7 6 ; Voeten et al, 1974). Erwin ( 1 9 5 5 ) was t h e first t o recover viable Salmonella from commercial p o u l t r y feed. O t h e r studies since have s h o w n t h a t t h e percentage of p o u l t r y mash samples c o n t a m i n a t e d with Salmonella organisms were 4% (Isa et al, 1963), 5% (Morehouse and W e d m a n , 1 9 6 1 ; Allred et al, 1967), 9% (Hobbs, 1 9 6 1 ) , 2 1 . 5 % (Morris et al, 1 9 6 9 ) , 4 3 . 5 % (MacKenzie a n d Bains, 1976), a n d 6 8 % (Cox et al, 1983). It is u n k n o w n w h e t h e r t h e higher percentages en-
c o u n t e r e d in m o r e recent studies reflected a true worsening of t h e problem o r resulted from i m p r o v e m e n t s in microbiological m e t h o d o l o g y for recovering Salmonella from feeds. Percentages of pelleted p o u l t r y feed f o u n d t o b e cont a m i n a t e d w i t h Salmonella were .7% (Allred et al, 1 9 6 7 ) , 1.7% (Hobbs, 1 9 6 1 ) , 4 . 3 % (Hacking et al, 1 9 7 8 ) , and 2 3 % (Cox et al, 1983). T h e objectives of this s t u d y were t o determine t h e effect of steam conditioning and pelleting of t w o types of p o u l t r y feed [broilerstarter (BS) a n d layer-breeder (LB)] on 1) t h e presence of Salmonella, n u m b e r s of Enterobacteriaceae, total n u m b e r s of bacteria and moisture at various locations in a commercial feed mill; 2) t h e t e m p e r a t u r e of t h e feed after t h e conditioning-pelleting process; and 3) t h e durability of t h e pellets. A small scale commercial feed mill, in which steam pressures for conditioning and feed types could be altered, was used in this s t u d y .
MATERIALS AND METHODS In a small scale commercial-type feed mill (University of Georgia) t w o types of p o u l t r y feed (BS a n d LB) were c o n d i t i o n e d at four different steam pressures [low (100 lb/hr); m e d i u m ( 2 0 0 l b / h r ) ; and high (300 lb/hr), t h e n
704
Downloaded from http://ps.oxfordjournals.org/ at Florida Atlantic University on November 13, 2014
ABSTRACT Effects of variations in steam conditioning and pelleting poultry feed to eliminate Salmonella were investigated in a commercial pellet mill. Layer-breeder and broiler-starter rations differing primarily in fat and limestone content were evaluated. Total bacteria counts were reduced only slightly, but Enterobacteriaceae counts were reduced appreciably by steam conditioning; however, pelleting was also necessary to eliminate Enterobacteriaceae consistently. Salmonella were present in about 50% of the feed samples before conditioning and in only about 4% of all samples after conditioning and pelleting. No Salmonella was detected after pelleting with high or very high steam pressure conditioning. Moisture content of the feed remained in an acceptable range regardless of steam pressure used. Temperature of the feed following the conditioning process was 134 to 135 F (57 C), 162 to 169 F (72 to 76 C), and 181 to 187 F (83 to 86 C) with low, medium, and high steam, respectively. The layer-breeder pellets were slightly more durable than the broiler-starter pellets, and overall pellet durability increased with increasing steam pressure. (Key words.- steam, pelleting, Salmonella, Enterobacteriaceae, temperature, feed)
STEAM, PELLETING ON POULTRY FEED
Model 8693-2 indicating Thermocouple Potentiometer equipped with a No. 30 Brown and Sharpe gauge duplex copper-constantan thermocouple. Feed (200 g) was collected in an insulated container; then thermocouples were immediately thrust into three different locations in the feed near the center of the container, and values were averaged. Pellet Durability Determination. The standard method for pellet durability of the American Society of Agricultural Engineers (ASAE, 1982) was used. Samples of whole pellets (500 g) were tumbled in a box for 10 min at 50 rpm, then screened. Pellet durability was expressed as the percentage of whole pellets recovered. This was replicated three times for both feed types and for low, medium, and high steam pressures. Statistical analysis of TPC and ENT were run with the general linear models procedure (SAS, 1985) using preplanned single degree of freedom contrasts to compare TPC and ENT before conditioning with each of the other three conditions. RESULTS AND DISCUSSION
Microbiology. The range of TPC before conditioning was small, only log 10 4.7 to 5.2 (Table 1). Small changes in TPC were observed as a result of the conditioning-pelleting process. The conditioning-pelleting operation is not intended to sterilize the feed; many microorganisms present in the feed, such as gram-positive sporeforming rods, and gram-positive cocci are more resistant to heat than Salmonella or other Enterobacteriaceae. The TPC per gram in the feed was generally logio 4 to 5 after conditioning and pelleting. Furuta et al. (1980) reported logio 4.5 total bacteria/g of mash and logio 1.1 total bacteria/g of pellets. Also, Cover et al. (1984) reported total bacteria counts similar to ours after conditioning and pelleting. We observed a slight increase in average TPC after cooling of the pellets. This may have been the result of blowing air from within the mill over the pellets to cool them. Riley (1969) reported a count of 20 to 200 microorganisms/ft 3 in a dusty feed mill. The ENT of feeds before conditioning ranged from logio 3.5 to 4.3 (Table 2). After conditioning with either low or medium steam pressure, there was little or no reduction of ENT. After high steam pressure conditioning, ENT were reduced to approximately logio 2.0.
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pelleted in a 40-hp California pellet mill with a 6.8-cm (2-2/3 in) die. Samples for microbiological analyses were aseptically taken before conditioning, after conditioning, after pelleting, and after cooling of the pellets. Separate samples were also taken to determine moisture levels, temperature of the feed after conditioning and pelleting, and durability of the pellets. Microbiological Analyses. Fifty grams of each sample were placed in a sterile screw cap jar with 450 ml of sterile buffered peptone (.1%) and vigorously shaken for 1 min. Serial dilutions were made and a total aerobic plate count (TPC) and an Enterobacteriaceae count (ENT) were run from the diluted sample. The pour plate technique with plate count agar (Difco) was used for the TPC and the plates were incubated at 35 to 37 C for 48 hr. From the same diluted samples, an ENT was determined [violet red bile with 1% glucose agar (Mossel et al, 1962)] with the pour plate technique plus an overlay. These plates were incubated at 3 5 C for 24 hr. For Salmonella determination, 50 g of feed were placed in a sterile container with 450 ml of sterile 1% buffered peptone (Juven et al., 1984), agitated for 30 sec with a sterile pipette, and incubated for 24 hr at 35 C. One milliliter was then aseptically transferred to tubes containing 10 ml of tetrathionate broth. These tubes were also incubated 24 hr at 35 C and then were streaked for isolation onto three selective plating media: BG sulfa, bismuth sulfite, and modified lysine iron agar (Rappold and Bolderdijk, 1979). After 24 hr at 35 C, two colonies with characteristics typical of Salmonella were selected from each plate and inoculated into lysine iron agar slants. Slants exhibiting a typical Salmonella reaction after 24 hr incubation at 35 C were streaked to determine purity and to produce isolated colonies on brain-heart infusion agar. Following 24 hr incubation at 35 C, the pure cultures were biochemically tested with Micro-ID (General Diagnostics, Morris Plains, NJ) and serologically tested with Poly O and H antisera to confirm the presence of Salmonella. Moisture Determination. Samples for moisture determination were taken at the same locations as the microbiological samples. Moisture was determined by drying duplicate 2-g samples in a forced draft oven (130 C) for 2 hr, averaging, then calculating weight loss. Temperature Determination. Temperature was measured with a Leeds and Northrup
705
4.4 a
4.5a
4.9 a
Mean
4.9 a 4.5a 4.3a 4.7 a
Mean
1.9a
2.7 D
3.0 b
Mean
1
3.5 1.7 0 2.4
3.7 3.4 1.1 2.7
3.7' 3.7 2.0 2.7
Before conditioner After conditioner After pelleter After cooling
4.3 4.5 0 2.3
3.6C 2.?bc 1.0a 2.6 b
Counts expressed as logarithms (base 10) of number per gram of feed.
2.8 a
Low
Mean
Conditioning steam pressure
' ' c Means within a column or row with different superscripts are significantly different (P = .05).
High
Medium
Low
Broiler-starter
TABLE 2. Enterobacteriaceae counts in broiler-starter and layer-breeder feed in a comme with low, medium, and high steam pressure conditioning
Counts expressed as logarithms (base 10) of number per gram of feed.
Sampling location
1
4.8 a
5.2 5.0 4.7 4.3
Low
Conditioning steam pressure
a ' b Means within a column or row with different superscripts are significantly different (P = .05). i
5.0 4.0 3.8 4.6
4.7 4.8 4.2 4.4
4.8 1 4.8 4.7 5.0
Before conditioner After conditioner After pelleter After cooling
High
Medium
Low
Sampling location
Broiler-starter
TABLE 1. Total plate count in broiler-starter and layer-breeder feed in a commerci with low, medium, and high steam pressure conditioning
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STEAM, PELLETING ON POULTRY FEED
Seven of the 12 samples of LB were positive for Salmonella before conditioning, but Salmonella were not detected in any samples after conditioning, pelleting, or cooling (Table 3). Five of the 12 samples of BS were positive for Salmonella before conditioning, and 1 was positive after conditioning, 1 after pelleting, but none after cooling. Cover et al. (1984) reported similar results in that they encountered an occasional Salmonella-positive sample after conditioning and pelleting. Conditioning with the high steam pressure appeared to give the best results; no Salmonella nor ENT was detected in
TABLE 3. Salmonella in broiler-starter and layer-breeder feed in a commercial feed pelleting mill with low, medium, and high steam pressure conditioning Before conditioner
After conditioner
After pelleter
After cooling
Type of feed
Steam pressure
Broiler-starter
Low
1/41
Medium High
3/4 1/4
1/4 0/4 0/4
0/4 1/4 0/4
0/4 0/4 0/4
5/12
1/12
1/12
0/12
4/4 3/4 0/4
0/4 0/4 0/4
0/4 0/4 0/4
0/4 0/4 0/4
7/12
0/12
0/12
0/12
12/24
1/24
1/24
0/24
Layer-breeder
Low
Medium High Total 1
Number of positive samples/number of samples tested.
TABLE 4. Moisture content (%) of broiler-starter and layer-breeder feed in a commercial feed pelleting mill with low, medium, and high steam pressure conditioning Steam pressure
Sampling location
Broilerstarter
Layerbreeder
Low
Before conditioner After conditioner After pelleter After cooling
12.1 13.2 13.1 11.6
11.6 13.2 13.5 11.9
Medium
Before conditioner After conditioner After pelleter After cooling
11.8 13.5 13.5 11.9
11.6 13.9 13.7 11.9
High
Before conditioner After conditioner After pelleter After cooling
11.9 15.5 14.9 12.8
11.7 13.9 14.1 11.9
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After pelleting, no ENT were found in any of the LB samples regardless of steam pressure. However, ENT were found in BS feed after low and medium but not after high steam pressure conditioning. Differences between BS and LB may have been caused by the higher fat content and thus greater lubricity of BS in the pelleter diet. The LB feed was also higher in limestone, which may have increased friction in the die, thereby increasing temperature. We found ENT in all samples of pellets after cooling; ENT were probably from recontamination by the feed mill equipment and environment.
COX ET AL.
708
any of t h e samples following t h e conditioningpelleting process. A very high s t e a m pressure ( 3 5 0 l b / h r ) conditioning was also tried. N o Salmonella o r E N T was d e t e c t e d in any of t h e samples following conditioning or t h e conditioning-pelleting process; however, t h e pellet mill did n o t o p e r a t e efficiently at this pressure. Within 5 t o 10 min at very high steam pressure, t h e pellet mill would b e c o m e clogged and would n o longer properly pellet t h e feed. Therefore this s t e a m pressure was n o t studied further.
TABLE 5. Temperature of broiler-starter and layer-breeder feed after the conditioner-pelleting process in a commercial feed pelleting mill with low, medium, and high steam pressure conditioning Type of feed Steam pressure
Broilerstarter
Low Medium High
57 72 83
Layerbreeder (°C) 57 77 87
1 Average temperature determinations made at three different locations in the feed sample.
Replication 2 3
Type of feed
Steam pressure
1
Broiler-starter
Low Medium High
52 1 54 60
56 56 62
56 56 63
Layer-breeder
Low Medium High
64 71 77
66 72 79
66 72 78
1
Percent of whole pellets recovered.
ACKNOWLEDGMENTS We t h a n k Mike Ban, Marty French, and Debbie Posey for their very able technical assistance and J o y Cornelius and Sandra Willis for their very able clerical assistance. M e n t i o n of specific b r a n d names does n o t imply e n d o r s e m e n t b y t h e authors or institut i o n s a t w h i c h t h e y are e m p l o y e d t o t h e exclusion of o t h e r p r o d u c t s n o t m e n t i o n e d .
REFERENCES AUred, J. N., J. W. Walker, V. C. Beal, Jr., and F. W. Germaine, 1967. A survey to determine the salmonella contamination rate in livestock and poultry feeds. J. Am. Vet. Med. Assoc. 151: 1857-1860. American Society of Agricultural Engineers, 1982. ASAE Yearbook 1982-1983. ASAE S 269.3. Cover, M. S., J. T. Gary, and S. F. Binder, 1984. Reduction of standard plate counts, total coliform counts and Salmonella by pelletizing animal feed. Pages 221-231 in Proc. Int. Symp. Salmonella, New Orleans, LA. Cox, N. A., J. S. Bailey, and J. E. Thomson, 1983. Comparison of preenrichment to direct enrichment and the effect of pyruvate in media for recovery of salmonellae in feed. Poultry Sci. 62: 947-951. Erwin, L. E., 1955. Examination of prepared poultry feeds for the presence of Salmonella and other enteric organisms. Poultry Sci. 34:215—216. Furuta, K., I. Oku, and S. Morimoto, 1980. Effect of steam temperature in the pelleting process of chicken food on the viability of contaminating bacteria. Lab. Anim. 14:293-296. Hacking, W. C , W. R. Mitchell, and H. C. Carlson, 1978. Salmonella investigation in an Ontario feed mill. Can. J. Comp. Med. 42:400-406. Hobbs, B. C , 1961. Public health significance of Salmonella carriers in livestock and birds. J. Appl. Bacteriol. 24:340-352.
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Moisture. T h e values for moisture of t h e feed r e m a i n e d in an acceptable range regardless of steam pressure (Table 4 ) . Temperature. Feed after t h e conditioningpelleting process was 134 t o 135 F (57 C) with low steam pressure, 162 F (72 t o 76 C) with m e d i u m , and 1 8 1 t o 1 8 7 F (83 t o 8 6 C) w i t h high (Table 5). Mossel et al. ( 1 9 6 7 ) r e p o r t e d a 1 0 3 r e d u c t i o n of ENT in feed pelleted at 51 t o 6 7 C a n d a 1 0 5 r e d u c t i o n at 8 0 t o 83 C. S t o t t et al. ( 1 9 7 5 ) f o u n d a 10 2 to 1 0 3 r e d u c t i o n of ENT/g of feed after heating t o 63 t o 85 C, and coliforms were eliminated from feed w h e n pelleting was performed at over 8 0 C ( F u r u t a et al, 1 9 8 0 ) . Tellet Durability. Durability of t h e pellets was superior at higher steam pressures and LB pellets were m o r e durable t h a n BS pellets, possibly because of a lower percentage of fat in t h e LB pullets (Table 6 ) . F u r t h e r investigations are u n d e r w a y t o d e t e r m i n e t h e effect of pelleting rate and size of openings in t h e die o n survival of Salmonella and o t h e r E N T in various types of p o u l t r y feed.
TABLE 6. Average durability of pellets from broiler-starter and layer-breeder feed obtained from a commercial feed pelleting mill with low, medium, and high steam pressure conditioning
STEAM, PELLETING ON POULTRY FEED
dium for the selective growth and enumeration of Enterobacteriaceae. J. Bacteriol. 84:381. Mossel, D.A.A., M. van Schothorst, and E. H. Kampelmacher, 1967. Comparative study on decontamination of mixed feeds by radicidation and by pelletization. J. Sci. Food Agric. 18:362. Rappold, H., and R. F. Bolderdijk, 1979. Modified lysine iron agar for isolation of Salmonella from food. Appl. Environ. Microbiol. 38:162—163. Riley, P. B., 1969. Salmonella infection: the position of animal food and its manufacturing process. Page 101 in Bacterial Food Poisoning. J. Taylor, ed. R. Soc. Health, London. SAS Institute, Inc., 1985. SAS User's Guide: Statistics. 5th ed. Cary, NC. Stott, J. A„ J. E. Hodgson, and J. C. Chaney, 1975. Incidence of salmonellae in animal feed and the effect of pelleting on content of Enterobacteriaceae. J. Appl. Bacteriol. 39:41-46. Voeten, A. C , D.H.J. Brus, and F.H.J. Jaartsveld, 1974. Distribution of Salmonella within a closed broiler chicken operation. Tydsk. Diergeneeskd. 99:1093-1094.
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Isa, J. M., B. R. Boycott, and E. Broughton, 1963. A survey of Salmonella contamination in animal feed and feed constituents. Can. Vet. J. 11:41 — 43. Juven, B. J„ N. A. Cox, J. S. Bailey, J. E. Thomson, O. W. Charles, and J. V. Schutze, 1984. Recovery of Salmonella from artificially contaminated poultry feeds in nonselective and selective broth media. J. Food Prot. 47:299-302. MacKenzie, M. A., and B. S. Bains, 1976. Dissemination of Salmonella serotypes from raw feed ingredients to chicken carcasses. Poultry Sci. 55:957— 960. Morehouse, L. G., and E. E. Wedman, 1961. Salmonella and other disease-producing organisms in animal by-products—a survey. J. Am. Vet. Med. Assoc. 139:989-995. Morris, G. K., B. L. McMurray, M. M. Galton, and J. G. Wells, 1969. A study of the dissemination of salmonellosis in a commercial broiler chicken operation. Am. J. Vet. Res. 30:1413-1421. Mossel, D.A.A., W.H.J. Mengerink, and H. H. Schotts, 1962. Use of a modified MacConkey agar me-
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