- Email: [email protected]
Some microbiological assays of ground beef blended with hydrogenated soybean oil
Meat Science 28 {1990) 245-249
Some Microbiological Assays of Ground Beef Blended with Hydrogenated Soybean Oil I. M. Tibin Department of Animal Husbandry, Institute of Animal Production, University of Khartoum, PO Box 32, Khartoum North, Sudan
& C. C. Melton Department of Food Technology and Science, PO Box 1071, University of Tennessee, Knoxville, Tennessee, 37901, USA (Received 11 May 1989; revised version received 8 December 1989; accepted 13 December 1989)
A BSTRA CT Ground beef patties were formulated from beef lean, beef fat and hydrogenated soybean oil. Using the Pearson Square Method, the patties were formed to contain three total fat levels (16, 20 and 24%). A t each level, vegetable fat was substituted for O, 25 or 50% of total fat to end up with nine different blends. Aerobic psychrotrophs andmesophiles of the blends were investigated at 0-, 3- and 6-day intervals. A split-split plot design with two replications was used to differentiate significant and non-significant attributes of the main effect and the corresponding interactions. Results obtained show that total fat level, percentage vegetable fat or replication did not have a significant effect on bacterial numbers of ground beef extended with hydrogenated soybean oil of 70 iodine value. However, the days of storage significantly (P < 0"001) affected both the Standard Plate Count (SPC) and Psychrotrophic Plate Count ( PPC ). The log number of bacteria in both S PC and P PC continued to increase with length of storage. In all the cases studied PPC was found to be higher than SPC, which indicates that the predominant microflora in raw beef products is psychrotrophic in nature. 245
Meat Science 0309-1740/90/$03.50 © 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain
246
L ~l,[. Tibin, C. C. Melton
INTRODUCTION Ground beef is one of the most economical and popular choices of meat products that offers consumers variety and convenience. However, it provides an excellent environment for microbial growth and becomes contaminated as a result of grinding and mixing during the fabrication process (Emswiler et al., 1976). The overall bacteriological quality of ground beef depends upon the bacterial population of beef trimmings, sanitation during processing, type of packaging and time and temperature of storage. Recently many vegetable proteins have been blended with different meat products. However, many research workers (Stansbury, 1975; Keeton, 1977; Harrison et al., 1981) have reported that bacterial numbers increased with the increase of percentage vegetable proteins in blended meat products. This research was conducted to investigate the effect of vegetable fat on the microbial flora of blended ground beef products.
MATERIALS A N D METHODS
Source of material for ground beef blends Beef fat and beef lean used in this study were purchased from a local packing company, the beef being USDA Standard Grade. Short plates were used as the source of beef fat. The plates were boned and then ground through a coarse 0.6cm mincing plate. The beef lean was trimmed to a minimum amount of fat and ground through a 0-6cm mincing plate. Following the initial grinding the beef lean and beef fat were mixed separately for about 2 min each in a mechanical mixer. Random samples were taken for fat content determinations according to the Babcock procedure (AOAC, 1975). Hydrogenated soybean oil with 70 iodine value was supplied by a local company, cut with a knife into smaller pieces, and ground through a 0.6 cm mincing plate. Using the Pearson Square Method (Pearson & Tauber, 1984) ground lean, ground fat and hydrogenated soybean oil were formulated to contain three total fat levels (16, 20 and 24%). At each level vegetable fat was substituted for 0, 25 or 50% of the total fat, as shown in Table 1, to make patties of nine different blends. Each blend was thoroughly hand-mixed, ground through a 0.3 cm mincing plate and then three 150-g portions of each blend were placed in separate plastic trays and loosely wrapped with plastic wrap. The samples were stored at 4°C. At the end of 0, 3 and 6 days one portion of each blend was removed from storage and assayed for aerobic psychrotrophs and mesophiles as follows: 25 g were removed from each portion and blended with 225mi of distilled autoclaved water in the
Microbiology of ground beef-soybean oil blends
247
TABLE l General Design for Ground Beef Blends
Blends
I 2 3 (Control) a 5 6 IControl) 7 8 9 IControl)
Total
Animal
~t
~t
~getable
~t
(%)
(%)
~%)
16 16 16 20 20 20 24 24 24
8 12 16 10 15 20 12 18 24
8 (50) 4 (25) 0 10) 10 (50) 5 (25) 0 (0) 12 (50) 6 (25) 0 (0)
Stomacher Lab. Blender 400 (model No. BA 6021 Serial No. 6023) for 2 min. Sterilized ready-made bags were used to hold the samples during blending. Serial dilutions from 10-t to 10-7 were plated on Standard Plate Count (SPC) agar and incubated at 32°C for 48 h for aerobic mesophiles. The same SPC agar and 10 -1 to 10 -7 dilutions were used for the aerobic psychrotrophs and incubated at 4°C for 10days. Total bacterial numbers were determined on a Quebec Colony Counter according to the guidelines suggested in Standard Methods (APHA, 1972) and reported as log number of bacteria per gram of sample. Two replications were performed, each consisting of the nine blends (Table 1).
Statistical analysis A split-split plot design with two replications and random samplings were utilized to study the effects of total fat level (16, 20 and 24%), percentage vegetable fat (0, 25 and 50%), time (days of storage), and replication (two different lots of ground beef) on microbial numbers of ground beef with vegetable fat added. Analysis of variance was used to differentiate significant and non-significant attributes of the main effect and the corresponding interactions.
RESULTS A N D DISCUSSION Analysis of variance for the log number of bacteria per gram of ground beef extended with hydrogenated soybean oil is shown in Table 2. There was no significant difference (P > 0-05) among total fat levels, percentage vegetable
248
!. M. Tibin, C. C. Melton
TABLE
2
Analysis of Variance for Log Number of Bacteria Per G r a m of Meat Source
Total Fat Level (TFL) Replication Replication x TFL (Error A) Percentage Vegetable Fat (PVF) T F L x PVF Error B b Days of Storage" Linear Quadratic T F L x Days of Storage PVF x Days of Storage T F L x PVF x Days of Storage Error C a
Mean squares DF
SPC °
"~ 1 2 2 4 6 2 I 1 4 4 8 18
2.11 0.04 1-90 0-85 0'56 0.85 40.48"** 80.55*** 0-41 * 1.41"** 0"62* 0-14 0.14
PPC
1.09 0-05 0-78 0-51 0.13 0.22 39"91 *** 78.62*** 1-21" 0.19 0.28 0.04 0.07
° Standard plate count. h Represents Replication x PVF and Replication x T F L x PVF. c0, 3 and 6 days at 4-5~C. Represents Replication x Days of Storage + TFI x Replication x Days of Storage + PVF x Days of Storage x Replication + T F L × PVF x Days of Storage x Replication. *** P < 0.001. * P < 0-05.
fat or replication. These results indicate that neither kind nor amount of fat has significant effects on the number of bacteria, as is the case with textured vegetable protein (Stansbury, 1975; Keeton, 1977; Harrison et aL, 1981). The days of storage significantly affected (P < 0.001) both the Standard Plate Count (SPC) and the Psychrotropic Plate Count (PPC). The log number of bacteria (Table 3) increased with days ofstorage for both the SPC and PPC. When the sum of squares was partitioned by orthogonal polynomials, a linear effect was found for SPC but both linear and quadratic effects were found for PPC (Table 2). In all samples, the log numbers of PPC were higher than SPC (Table 3). These results agree with those reported in the literature (Rogers & McClesky, 1956; Duitschaever et al., 1973; Foster et al., 1978). This indicates that the predominant microflora in raw beef products is psychrotrophic in nature and that the current inoculation temperatures (i.e. 30, 32 and 35°C) for testing raw meat products without consideration of the psychrotrophic plate count should be re-evaluated. The same suggestion was given by Draughon (1980), who considered that psychrotropic and mesophilic
Microbiology' of ground beef-soybean oil blends
249
TABLE 3
Least Square Means for the Effectof Total Fat Level(%), Percentage Vegetable Fat, Days of Storage and Replication on the Log Numbers of Bacteria Per Gram of Meat
Treatment Total fat level (%) 16 20 24 Percentage vegetable fat 0 25 50 Days of storage 0 3 6 Replication 1
2
S PC {log nos)
PPC (log nos)
6.6 6.97 6-29
7.16 7.43 6.94
6.39 6.79 6-73
7.00 7.20 7-33
5.20 6.52 8.20
5.81 6.96 8.76
6-61 6-66
7.21 7.15
plate counts should be used in testing raw meat products and that a time temperature standard should be established so that results can be compared.
REFERENCES AOAC (1975). Official Methods of Analysis, 12th edn. Association of Official Analytical Chemists, Washington, DC. APHA (1972). Standard Methods for the Examination of Dairy Products, ed. William J. Hausle, Jr. American Public Health Association, Washington DC. Draughon, F. A. (1980). Food Technol., 34, 69. Duitschaever, C. L., Arnott, D. R. & Bullock, D. H. (1973). J. Milk Food Technol., 36, 375. Emswiler, B. S., Pierson, C. J. & Kotula, A. W. (1976). AppL Environ. Microbiol., 31, 826. Foster, J. F., Hunderfund, R. C., Fowler, J. L., Fruin, J. T. & Guthertz, L. S. (1978). J. Food Prot., 41,961. Harrison, M. A., Melton, C. C. & Draughton, F. A. (1981). J. Food Sci., 46, 1088. Keeton, J. T. (1977). PhD Dissertation, University of Tennessee, Knoxville. Pearson, A. M. & Tauber, F. W. (1984). Processed Meats, 2nd edn. AVI Publishing Co., West Port, CT. Rogers, R. E. & McCieskey, C. S. (1956). Food Technol., 11, 319. Stansbury, J. B. (1975). PhD Dissertation, University of Tennessee, Knoxville.
Some Microbiological Assays of Ground Beef Blended with Hydrogenated Soybean Oil I. M. Tibin Department of Animal Husbandry, Institute of Animal Production, University of Khartoum, PO Box 32, Khartoum North, Sudan
& C. C. Melton Department of Food Technology and Science, PO Box 1071, University of Tennessee, Knoxville, Tennessee, 37901, USA (Received 11 May 1989; revised version received 8 December 1989; accepted 13 December 1989)
A BSTRA CT Ground beef patties were formulated from beef lean, beef fat and hydrogenated soybean oil. Using the Pearson Square Method, the patties were formed to contain three total fat levels (16, 20 and 24%). A t each level, vegetable fat was substituted for O, 25 or 50% of total fat to end up with nine different blends. Aerobic psychrotrophs andmesophiles of the blends were investigated at 0-, 3- and 6-day intervals. A split-split plot design with two replications was used to differentiate significant and non-significant attributes of the main effect and the corresponding interactions. Results obtained show that total fat level, percentage vegetable fat or replication did not have a significant effect on bacterial numbers of ground beef extended with hydrogenated soybean oil of 70 iodine value. However, the days of storage significantly (P < 0"001) affected both the Standard Plate Count (SPC) and Psychrotrophic Plate Count ( PPC ). The log number of bacteria in both S PC and P PC continued to increase with length of storage. In all the cases studied PPC was found to be higher than SPC, which indicates that the predominant microflora in raw beef products is psychrotrophic in nature. 245
Meat Science 0309-1740/90/$03.50 © 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain
246
L ~l,[. Tibin, C. C. Melton
INTRODUCTION Ground beef is one of the most economical and popular choices of meat products that offers consumers variety and convenience. However, it provides an excellent environment for microbial growth and becomes contaminated as a result of grinding and mixing during the fabrication process (Emswiler et al., 1976). The overall bacteriological quality of ground beef depends upon the bacterial population of beef trimmings, sanitation during processing, type of packaging and time and temperature of storage. Recently many vegetable proteins have been blended with different meat products. However, many research workers (Stansbury, 1975; Keeton, 1977; Harrison et al., 1981) have reported that bacterial numbers increased with the increase of percentage vegetable proteins in blended meat products. This research was conducted to investigate the effect of vegetable fat on the microbial flora of blended ground beef products.
MATERIALS A N D METHODS
Source of material for ground beef blends Beef fat and beef lean used in this study were purchased from a local packing company, the beef being USDA Standard Grade. Short plates were used as the source of beef fat. The plates were boned and then ground through a coarse 0.6cm mincing plate. The beef lean was trimmed to a minimum amount of fat and ground through a 0-6cm mincing plate. Following the initial grinding the beef lean and beef fat were mixed separately for about 2 min each in a mechanical mixer. Random samples were taken for fat content determinations according to the Babcock procedure (AOAC, 1975). Hydrogenated soybean oil with 70 iodine value was supplied by a local company, cut with a knife into smaller pieces, and ground through a 0.6 cm mincing plate. Using the Pearson Square Method (Pearson & Tauber, 1984) ground lean, ground fat and hydrogenated soybean oil were formulated to contain three total fat levels (16, 20 and 24%). At each level vegetable fat was substituted for 0, 25 or 50% of the total fat, as shown in Table 1, to make patties of nine different blends. Each blend was thoroughly hand-mixed, ground through a 0.3 cm mincing plate and then three 150-g portions of each blend were placed in separate plastic trays and loosely wrapped with plastic wrap. The samples were stored at 4°C. At the end of 0, 3 and 6 days one portion of each blend was removed from storage and assayed for aerobic psychrotrophs and mesophiles as follows: 25 g were removed from each portion and blended with 225mi of distilled autoclaved water in the
Microbiology of ground beef-soybean oil blends
247
TABLE l General Design for Ground Beef Blends
Blends
I 2 3 (Control) a 5 6 IControl) 7 8 9 IControl)
Total
Animal
~t
~t
~getable
~t
(%)
(%)
~%)
16 16 16 20 20 20 24 24 24
8 12 16 10 15 20 12 18 24
8 (50) 4 (25) 0 10) 10 (50) 5 (25) 0 (0) 12 (50) 6 (25) 0 (0)
Stomacher Lab. Blender 400 (model No. BA 6021 Serial No. 6023) for 2 min. Sterilized ready-made bags were used to hold the samples during blending. Serial dilutions from 10-t to 10-7 were plated on Standard Plate Count (SPC) agar and incubated at 32°C for 48 h for aerobic mesophiles. The same SPC agar and 10 -1 to 10 -7 dilutions were used for the aerobic psychrotrophs and incubated at 4°C for 10days. Total bacterial numbers were determined on a Quebec Colony Counter according to the guidelines suggested in Standard Methods (APHA, 1972) and reported as log number of bacteria per gram of sample. Two replications were performed, each consisting of the nine blends (Table 1).
Statistical analysis A split-split plot design with two replications and random samplings were utilized to study the effects of total fat level (16, 20 and 24%), percentage vegetable fat (0, 25 and 50%), time (days of storage), and replication (two different lots of ground beef) on microbial numbers of ground beef with vegetable fat added. Analysis of variance was used to differentiate significant and non-significant attributes of the main effect and the corresponding interactions.
RESULTS A N D DISCUSSION Analysis of variance for the log number of bacteria per gram of ground beef extended with hydrogenated soybean oil is shown in Table 2. There was no significant difference (P > 0-05) among total fat levels, percentage vegetable
248
!. M. Tibin, C. C. Melton
TABLE
2
Analysis of Variance for Log Number of Bacteria Per G r a m of Meat Source
Total Fat Level (TFL) Replication Replication x TFL (Error A) Percentage Vegetable Fat (PVF) T F L x PVF Error B b Days of Storage" Linear Quadratic T F L x Days of Storage PVF x Days of Storage T F L x PVF x Days of Storage Error C a
Mean squares DF
SPC °
"~ 1 2 2 4 6 2 I 1 4 4 8 18
2.11 0.04 1-90 0-85 0'56 0.85 40.48"** 80.55*** 0-41 * 1.41"** 0"62* 0-14 0.14
PPC
1.09 0-05 0-78 0-51 0.13 0.22 39"91 *** 78.62*** 1-21" 0.19 0.28 0.04 0.07
° Standard plate count. h Represents Replication x PVF and Replication x T F L x PVF. c0, 3 and 6 days at 4-5~C. Represents Replication x Days of Storage + TFI x Replication x Days of Storage + PVF x Days of Storage x Replication + T F L × PVF x Days of Storage x Replication. *** P < 0.001. * P < 0-05.
fat or replication. These results indicate that neither kind nor amount of fat has significant effects on the number of bacteria, as is the case with textured vegetable protein (Stansbury, 1975; Keeton, 1977; Harrison et aL, 1981). The days of storage significantly affected (P < 0.001) both the Standard Plate Count (SPC) and the Psychrotropic Plate Count (PPC). The log number of bacteria (Table 3) increased with days ofstorage for both the SPC and PPC. When the sum of squares was partitioned by orthogonal polynomials, a linear effect was found for SPC but both linear and quadratic effects were found for PPC (Table 2). In all samples, the log numbers of PPC were higher than SPC (Table 3). These results agree with those reported in the literature (Rogers & McClesky, 1956; Duitschaever et al., 1973; Foster et al., 1978). This indicates that the predominant microflora in raw beef products is psychrotrophic in nature and that the current inoculation temperatures (i.e. 30, 32 and 35°C) for testing raw meat products without consideration of the psychrotrophic plate count should be re-evaluated. The same suggestion was given by Draughon (1980), who considered that psychrotropic and mesophilic
Microbiology' of ground beef-soybean oil blends
249
TABLE 3
Least Square Means for the Effectof Total Fat Level(%), Percentage Vegetable Fat, Days of Storage and Replication on the Log Numbers of Bacteria Per Gram of Meat
Treatment Total fat level (%) 16 20 24 Percentage vegetable fat 0 25 50 Days of storage 0 3 6 Replication 1
2
S PC {log nos)
PPC (log nos)
6.6 6.97 6-29
7.16 7.43 6.94
6.39 6.79 6-73
7.00 7.20 7-33
5.20 6.52 8.20
5.81 6.96 8.76
6-61 6-66
7.21 7.15
plate counts should be used in testing raw meat products and that a time temperature standard should be established so that results can be compared.
REFERENCES AOAC (1975). Official Methods of Analysis, 12th edn. Association of Official Analytical Chemists, Washington, DC. APHA (1972). Standard Methods for the Examination of Dairy Products, ed. William J. Hausle, Jr. American Public Health Association, Washington DC. Draughon, F. A. (1980). Food Technol., 34, 69. Duitschaever, C. L., Arnott, D. R. & Bullock, D. H. (1973). J. Milk Food Technol., 36, 375. Emswiler, B. S., Pierson, C. J. & Kotula, A. W. (1976). AppL Environ. Microbiol., 31, 826. Foster, J. F., Hunderfund, R. C., Fowler, J. L., Fruin, J. T. & Guthertz, L. S. (1978). J. Food Prot., 41,961. Harrison, M. A., Melton, C. C. & Draughton, F. A. (1981). J. Food Sci., 46, 1088. Keeton, J. T. (1977). PhD Dissertation, University of Tennessee, Knoxville. Pearson, A. M. & Tauber, F. W. (1984). Processed Meats, 2nd edn. AVI Publishing Co., West Port, CT. Rogers, R. E. & McCieskey, C. S. (1956). Food Technol., 11, 319. Stansbury, J. B. (1975). PhD Dissertation, University of Tennessee, Knoxville.