Evaluation of an 18°C/45-Hour Plate Count Technique for the Enumeration of Psychrotrophic Bacteria in Raw and Pasteurized Milk

1983 ◽  
Vol 46 (6) ◽  
pp. 528-529 ◽  
Author(s):  
HARRY K. OEHLRICH ◽  
ROBIN C. MCKELLAR
Keyword(s):  
Plate Count ◽  
Reliable Estimate ◽  
Additional Test ◽  
Bacterial Counts ◽  
Pasteurized Milk ◽  
Psychrotrophic Bacteria ◽  
Milk Samples

Bacterial counts were done at 7°C for 10 d and at 18°C for 45 h on 93 samples of raw and 185 samples of pasteurized milk. As an additional test, catalase-positive microorganisms were enumerated at 18°C/45 h. Close correlations were obtained between the numbers of microorganisms following 18°C/45-h and 7°C/10-d incubations in raw (r2=0.866) and pasteurized (r2=0.936) milk samples. Similar correlations (r2=0.860 and 0.946) were noted for the 18°C/45-h-catalase and the 7°C/10-d methods for raw and pasteurized milk, respectively. Results suggest that incubation at 18°C for 45 h provides a reliable estimate of the numbers of psychrotrophs in raw and pasteurized milk and that the use of catalase does not improve sensitivity of the test significantly.

Preliminary Incubation Count as an Index of Raw Milk Microbiological Quality During Storage

1984 ◽  
Vol 47 (3) ◽  
pp. 206-208 ◽  
Author(s):  
J. J. RYAN ◽  
R. H. GOUGH ◽  
C. H. WHITE
Keyword(s):  
Microbiological Quality ◽  
Storage Period ◽  
Raw Milk ◽  
Plate Count ◽  
Bacterial Counts ◽  
Sample Group ◽  
Psychrotrophic Bacteria ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Standard Plate

During a 5-month period, 200 raw milk samples were collected from two Louisiana milk plants. Standard Plate Count (SPC), Psychrotrophic Bacteria Count (PBC), and Proteolytic Count (PC) of each sample were initially determined, then monitored daily during a 5-d storage period at 2.2°C. As hypothesized, all bacterial counts increased during the storage period. The magnitude of the increase in bacterial numbers during storage was further investigated by dividing the milk samples into bacteriologically acceptable and unacceptable groups based on SPC or Preliminary Incubation (PI) count. An SPC of 1.0 × 105/ml and PI counts of 1.0 × 105/ml, 1.5 × 105/ml, 2.3 × 105/ml, and 3.0 × 105/ml were used to repeatedly dichotomize the 200 raw milk samples into two groups. Median SPC, PBC, and PC for each acceptable and unacceptable group were then calculated. Dichotomization based on PI counts yielded acceptable sample groups having consistently lower bacterial counts during storage than did the acceptable sample group, which resulted from the dichotomization based on a SPC of 1.0 × 105/ml. The results of this study indicated that the PI count is of considerable value for raw milk quality control.

Heat-Resistant Psychrotrophic Bacteria Isolated from Pasteurized Milk1

1977 ◽  
Vol 40 (2) ◽  
pp. 101-108 ◽  
Author(s):  
C. J. WASHAM ◽  
H. C. OLSON ◽  
E. R. VEDAMUTHU
Keyword(s):  
Thermal Resistance ◽  
Shelf Life ◽  
Detailed Examination ◽  
Genus Bacillus ◽  
Pasteurized Milk ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
Heat Resistant ◽  
Different Types

Psychrotrophic bacteria were isolated from 227 pasteurized milk samples which had a shelf life in excess of 20 days at 7.2 C. Of 700 cultures isolated, 135 were resistant to heating at 72 C for 16 sec and were able to re-establish growth at 7.2 C. Thirty-five cultures, representing 15 different types were subjected to detailed examination to determine their actions on refrigerated milk, growth temperatures, thermal resistance at various temperatures, and their identities. The spore-forming genus Bacillus occured most frequently. The non-sporing types were assigned to the genera Arthrobacter, Microbacterium, Streptococcus, and Corynebacterium.

Comparison between the EC plate count test at 21 °C and an accelerated plate count method for assessing the keeping quality of pasteurized milk

1992 ◽  
Vol 59 (3) ◽  
pp. 431-436 ◽  
Author(s):  
Sarah A. Langford ◽  
Rohan G. Kroll
Keyword(s):  
Plate Count ◽  
Gram Negative ◽  
Rapid Methods ◽  
Pasteurized Milk ◽  
Psychrotrophic Bacteria ◽  
Commercial Interest ◽  
Count Method ◽  
Keeping Quality ◽  
Plate Count Method

The keeping quality of properly refrigerated pasteurized milk and cream is primarily determined by post-pasteurization contamination by Gram-negative psychrotrophic bacteria (Phillips et al. 1981; Schröder et al. 1982). Reliable and rapid methods of assessing the levels of contamination by these organisms are therefore of commercial interest.

BACTERIAL COUNTS OF RAW MILK AND FLAVOR OF THE MILK AFTER PASTEURIZATION AND STORAGE

1972 ◽  
Vol 35 (4) ◽  
pp. 203-206 ◽  
Author(s):  
G. B. Patel ◽  
G. Blankenagel
Keyword(s):  
Raw Milk ◽  
Bacterial Counts ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
Standard Plate ◽  
Plate Counts ◽  
Subsequent Storage ◽  
And Storage ◽  
Common Defect

A total of 216 raw milk samples with a variety of Standard Plate Counts and psychrotrophic bacteria counts were laboratory-pasteurized, stored at 7 C, and then evaluated for flavor after 1 and 2 weeks. Results showed that milk with counts of >1,000,000/ml before heating frequently developed objectionable flavors after pasteurization and subsequent storage. The most common defect was a bitter flavor which appeared within 2 weeks after pasteurization in nearly all samples which as raw milk had counts exceeding 10,000,000/ml. This off-flavor developed in spite of small numbers of organisms in the pasteurized product and in the absence of post-pasteurization contamination.

Rapid Detection of Psychrotrophic Bacteria In Manufacturing Grade Raw Milks

1991 ◽  
Vol 54 (11) ◽  
pp. 861-867 ◽  
Author(s):  
S. R. TATINI ◽  
P. MEKALA ◽  
A. EL-HABAZ ◽  
M. W. GRIFFITHS
Keyword(s):  
Rapid Detection ◽  
Bacterial Count ◽  
Raw Milk ◽  
Plate Count ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
Microscopic Count ◽  
Direct Epifluorescent Filter Technique ◽  
Native Microflora

Methods to rapidly assess the bacteriological quality of raw milk were investigated. Whereas direct microscopic count, modified psychrotrophic plate count, and direct epifluorescent filter technique (DEFT) did not correlate well with initial psychrotrophic bacterial count of raw milk, improvements were obtained after preincubation of the milk samples. The best preincubation conditions were identified as 30°C for 6 h, 21°C for 10 h, 13°C for 15 h, 13°C for 20 h, or 7°C for 37 h. The “square root” equation was applied to the data, and a model was produced for predicting growth of the native microflora of raw milk. Using this equation, a DEFT count after preincubation of the milk at 21°C for 10 h could accurately predict the initial psychrotroph count and the count after storage of the milk at 6°C for 48 h.

Molecular Analysis of Spoilage-Related Bacteria in Pasteurized Milk during Refrigeration by PCR and Denaturing Gradient Gel Electrophoresis

2009 ◽  
Vol 72 (3) ◽  
pp. 572-577 ◽  
Author(s):  
HONGFEI HE ◽  
JIN DONG ◽  
CHIN NYEAN LEE ◽  
YONG LI
Keyword(s):  
Shelf Life ◽  
Gel Electrophoresis ◽  
Denaturing Gradient Gel Electrophoresis ◽  
Plate Count ◽  
Pasteurized Milk ◽  
Milk Samples ◽  
Gradient Gel Electrophoresis ◽  
Aerobic Plate Count ◽  
Species Specific

Bacterial diversity in fluid milk products has been extensively studied in order to improve milk quality. Here, we illustrate the utility of viable counts and PCR–denaturing gradient gel electrophoresis (DGGE) for monitoring the microbial spoilage of pasteurized milk during shelf life. Five pasteurized milk samples stored at 4°C were examined at 10 and 5 days before expiration and on the expiration day. With bacterial DNA extracted directly from the samples, PCR-DGGE analysis indicated that Pseudomonas became dominant in four samples. Meanwhile, the aerobic plate count of these four samples exceeded the regulatory limit of 20,000 CFU/ml at 5 days before expiration, and the rapid psychrotrophic count markedly surpassed the aerobic plate count on the expiration day. Streptococcus and Buttiauxella spp. were detected in several samples. Sequence analysis of DGGE fragments revealed high diversity among Pseudomonas spp. in the milk samples. P. putida and P. migulae grew to high numbers during refrigerated storage. Further identification of Pseudomonas at the species level was facilitated by PCR and multiplex PCR using species-specific primers; consequently, P. fluorescens and P. fragi were observed. These results highlight an important role of Pseudomonas in the shelf life of pasteurized milk.

THE EFFECT ON BACTERIAL COUNTS OF THE GRADUAL WARMING OF MILK SAMPLES

1963 ◽  
Vol 26 (12) ◽  
pp. 389-391
Author(s):  
J. L. Courtney
Keyword(s):  
Room Temperature ◽  
Bacterial Counts ◽  
Pasteurized Milk ◽  
Milk Samples ◽  
Average Maximum ◽  
Standard Plate ◽  
Plate Counts

Summary Samples of retail pasteurized milk were allowed to stand at room temperature for 4 hr during which the temperature of the samples increased 33 F to an average maximum of 81 F. Coliform and standard plate counts were made during this period. Only 2 samples out of 16 showed extensive coliform growth. Increases in standard plate counts were surprisingly small.

scholarly journals Prevalence of Psychrotrophic Bacteria During Frozen Storage of Raw Milk

2021 ◽  
Vol 24 (1) ◽  
pp. 65-76
Author(s):  
S Ahmed ◽  
S MMR Sumon ◽  
MD Hossain ◽  
ABM Rubayet Bostami ◽  
MM Rahman
Keyword(s):  
Management Practices ◽  
Bacterial Load ◽  
Frozen Storage ◽  
Storage Period ◽  
Dairy Farms ◽  
Raw Milk ◽  
Plate Count ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
Large Farms

The study was aimed to enumerate the load of psychrotrophic bacteria in raw milk stored in freezer. Raw milk was collected from 18 different sized dairy farms located in Gazipur and Mymensingh district. From each location equal number (three of each) of small, medium or large farms were randomly selected. The raw milk samples were stored in freezer (-18 to -22 oC) for 28 days and analyzed for psychrotrophic bacterial load at every 7 days interval. For total viable count, bacteria was grown onto plate count agar at 70C for 10 days. Bacteria grown under such conditions referred as psychrotrophs. However, to determine the type of psychrotrophs selected colonies were grown further onto pseudomonas agar base and gram staining, oxidase, catalase and methyl red test for each isolate were perfomed. The psychrotrophic bacterial load in all the samples were low until 14 days of storage. However, from the third week of storage the bacterial load was observed to increase which reached to as high as 1.1 ± 2.3×107 cfu/mL at the end of the storage period (28 days). The milk samples obtained from large farms were lower (1.3×105 to 6.6×106) than that of medium (1.7×105 to 8.8×106) and small (2.0×105 to 1.1×107) type farms. The bacterial load was significantly (P<0.01) varied among the samples suggesting the heterogeneous management practices in dairy farms. All the morphological and biochemical tests confirmed the isolates as pseudomonas. Based on the present findings, it could be suggested that raw milk can store in the freezer maximum for two weeks in terms of psychrotrophic bacterial load. Ann. Bangladesh Agric. (2020) 24(1) : 65-76

scholarly journals Stability of Lactic Acid Bacteria in Pasteurized Cow’s and Goat’s Milk

2019 ◽  
Vol 1 (4) ◽  
pp. 77-82
Author(s):  
Nurfarhana Syed Malik ◽  
Mohd. Nizam Lani ◽  
Fauziah Tufail Ahmad
Keyword(s):  
Lactic Acid ◽  
Lactic Acid Bacteria ◽  
Viable Count ◽  
Plate Count ◽  
Pasteurized Milk ◽  
Milk Samples ◽  
Goat’S Milk ◽  
Different Types ◽  
Goat's Milk ◽  
The Stability

This study was done to determine the effect of pasteurization on the stability of lactic acid bacteria (LAB) and its enzyme in raw and pasteurized cow’s and goat’s milk. The total viable count for plate count of the bacterial growth concentration was higher in both pasteurized cow’s and goat’s milk at 2.48 log CFU/ml. This is followed by raw cow’s milk (1.59 log CFU/ml) and raw goat’s milk (0.65 log CFU/ml). Lactic acid bacteria (LAB) was found to be similar in both raw cow’s and goat’s milk (p>0.05), and pasteurized milk of both animals also contained the same amount of LAB (p>0.05). LAB was still detected in pasteurized milk (p<0.05), indicating the stability of LAB against the pasteurization temperature. Interestingly, based on API ZYM assay kit results, there were nine different enzymes detected in all samples, which were leucinearylamidase, valinearylamidase,cystinearylamidase, trypsin, α-chymotrypsin, naphthol-AS-BI-phosphohydrolase, α-glucosidase, β-glucosidaseand acid phosphatise. The results revealed that different types of lactic acid bacteria were detected in treated and non-treated milk samples produced by different animals, indicating the different stability levels of LAB against pasteurization.

EFFECT OF PIPETTE TYPE AND SAMPLE SIZE ON PLATE COUNT RESULTS

1965 ◽  
Vol 28 (10) ◽  
pp. 314-319 ◽  
Author(s):  
E. H. Marth ◽  
J. F. Proctor ◽  
R. V. Hussong
Keyword(s):  
Statistical Analysis ◽  
Standard Deviation ◽  
Sample Size ◽  
Raw Milk ◽  
Plate Count ◽  
Test Results ◽  
Pasteurized Milk ◽  
Milk Samples ◽  
Large Numbers ◽  
Points Of View

Summary Raw and pasteurized milk samples were plated by seven analysts using 0.1- and 1.0-ml quantities (of appropriate dilutions) dispensed by 0.1-ml glass, 1.1-ml plastic and 1.1- and 2.2-ml glass pipettes. Incubation was at 32 C for 48 hr. Data were subjected to an analysis of variance and the standard deviation as a ratio was calculated. The procedures were compared from two points of view, first to determine if biases existed between the different methods and second if the techniques differed in their random error. No appreciable differences were found between types of pipettes when pasteurized milk was plated. The quantity used, however, was important. Use of a 0.1-ml sample size was associated with more variable results which averaged 10% higher than when a 1.0-ml quantity was plated. Statistical analysis of test results obtained with pasteurized milk suggests: (a) when 0.1-ml samples were used least variation was encountered with the 0.1-ml glass pipette and most variation with the 1.1-ml glass pipette, and (b) when 1.0-ml samples were used very little difference appeared between pipettes although the 1.1-ml plastic pipette tended toward less variation. When raw milk contained large numbers of bacteria, the plastic pipette tended to give higher results than glass pipettes when the 1.0-ml quantity was used; however, these differences with raw milk were not found to be statistically significant. Standard deviations as a ratio revealed: (a) greatest variation with the 2.2-ml glass pipette and least with a 0.1-ml glass or 1.1-ml plastic pipette when a 0.1-ml quantity was used, and (b) greatest variation with a 1.1-ml plastic pipette and least with a 2.2-ml glass pipette when a 1.0-ml sample size was used.

Sign in / Sign up

Export Citation Format

Share Document