Comparing Three Methods for Counting Raw-Milk Pour Plates1

1979 ◽  
Vol 42 (9) ◽  
pp. 729-731
Author(s):  
J. A. WESLEY ◽  
B. E. LANGLOIS ◽  
J. O'LEARY
Keyword(s):  
Raw Milk ◽  
Regression Equations ◽  
Standard Methods ◽  
Manual Count ◽  
Milk Samples ◽  
Plate Counts ◽  
Electronic Probe ◽  
The Difference ◽  
Incubation Temperatures ◽  
Colony Counter

Six hundred Grade A raw milk samples were plated on Standard Methods agar and the pour-plate counts compared using three methods. Counts of each sample were determined after incubation at 26, 30 and 32 C for 72 h with an automatic colony counter (ACC). Quebec colony counter and hand tally (HT) and Quebec colony counter and electronic probe with digital register (DT). No significant differences were found between the counts obtained with the HT and the DT for any of the three incubation temperatures. The ACC counts were lower (P < .01) than the manual counts at each temperature. The ACC counts were .39, .35 and .31 log counts lower than the manual count at 26, 30 and 32 C, respectively. The ACC counts at 72 h were higher (P < .01) than the ACC counts at 48 h for all temperatures. The difference was about .41 log counts. The two manual counts were totally correlated, while the correlation between the ACC counts and the manual count; was 97. Regression equations were formulated for predicting the 72 h HT count from either the 48 or 72 h ACC count.

Effect of Five Surface Area-to-Sample Volume Ratios During Preliminary Incubation on The Bacterial Count of Raw Milk1,2

1979 ◽  
Vol 42 (12) ◽  
pp. 968-970
Author(s):  
J. A. RITTER ◽  
B. E. LANGLOIS ◽  
J. O'LEARY
Keyword(s):  
Surface Area ◽  
Incubation Temperature ◽  
Bacterial Count ◽  
Raw Milk ◽  
Sample Volume ◽  
Bacterial Counts ◽  
Milk Samples ◽  
Standard Plate ◽  
Plate Counts ◽  
Incubation Temperatures

Effects of ratio of surface area to volume of sample during preliminary incubation (PI) and of different plate incubation temperatures on bacterial counts of raw milk samples were studied. One hundred and twenty Grade A raw milk samples collected during a 10-month period were divided into five 100-ml aliquots and allotted to one of five surface area to volume ratios. The ratios during PI ranged from 0 cm2/100 ml to 149.74 cm2/100 ml. Following PI, pour plates of each treatment were incubated at 26, 30 and 32 C for 72 h. The Standard Plate Counts (SPC) ranged from 89 × 101 to 20 × 108/ml, with the SPC of 73.6% of the samples being less than 1 × 105/ml. Counts after PI tended to be higher as the plate incubation temperature decreased from 32 to 26 C and as the ratio of surface area to volume of sample increased. None of the differences between the counts for the 15 treatment-incubation temperatures was significant. Counts of 61 samples increased less than one log count during PI, while counts of 33 and 16 samples increased one to two log counts and over two log counts, respectively. The greater the SPC, the smaller the increase in count during PI. Of the 81 samples with SPC less than 1 × 105/ml, 29 had counts after PI that exceeded 2 × 105/ml.

INCUBATION TEMPERATURES AND RAW MILK BACTERIAL COUNTS

1968 ◽  
Vol 31 (5) ◽  
pp. 154-160 ◽  
Author(s):  
C. N. Huhtanen
Keyword(s):  
Raw Milk ◽  
The Other ◽  
Bacterial Counts ◽  
Milk Samples ◽  
Significant Difference ◽  
The Difference ◽  
Incubation Temperatures

Raw milk samples were plated and incubated at seven temperatures (2, 10, 20, 27, 30, 33 and 37 C). Lowest counts were obtained at 37 C. Plates at 33 C showed higher counts than at 37 C but were significantly lower than the other temperatures. The 10, 20, 27 and 30 C incubated plates were not statistically different in counts. When 32 C was substituted for 33 C, there was a significant difference (lower) only in the 37 C count. Colonies from 2, 20, 27, 33 and 37 C plates were picked and stabbed into plates subsequently incubated at these temperatures. All colonies developed best at 20 and 27 C. Evidence is presented that psychrophilic counts can be indirectly determined as the difference between counts at 27 C and 37 C.

EFFECTS OF MEDIUM AND INCUBATION TEMPERATURE ON RECOVERY OF MICROORGANISMS FROM MANUFACTURING-GRADE, GRADE-A AND PASTEURIZED MILK1

1969 ◽  
Vol 32 (3) ◽  
pp. 90-93
Author(s):  
J. C. Hartley ◽  
G. W. Reinbold ◽  
E. R. Vedamuthu
Keyword(s):  
Incubation Temperature ◽  
Raw Milk ◽  
Optimum Temperature ◽  
Standard Methods ◽  
Pasteurized Milk ◽  
Milk Samples ◽  
Significant Difference ◽  
The Mean ◽  
Incubation Temperatures ◽  
Temperature Time

Recovery of microorganisms by Standard Methods Agar and Eugonagar was compared at 7, 21, 28, and 32C incubation temperatures for 10, 5, 4, and 2 days, respectively, from manufacturing-grade, grade-A, and pasteurized milk. The incubation temperature made a statistically significant difference in the mean logarithm of the count for all three grades of milk. The highest mean logarithm of the count with manufacturing-grade milk was obtained at 21 C for both agars. With grade-A raw milk, the greatest mean logarithm of the count was obtained at 21 C for Standard Methods Agar and at 28 C for Eugonagar. The highest mean logarithm of the count for pasteurized milk was obtained at 28 C with Standard Methods Agar and at 21 C with Eugonagar. There was a significant difference between means on Standard Methods Agar and Eugonagar on grade-A milk samples only; recovery was highest with Eugonagar. Because of the presence of psychrophilic microorganisms, an incubation temperature lower than 32 C is needed for maximum recovery. Incubation at 28 C for 4 days was the optimum temperature-time combination in this study.

Determination of Viable Bacterial Populations in Raw Milk within 20 Minutes by Using a Direct Epifluorescent Filter Technique

1997 ◽  
Vol 60 (7) ◽  
pp. 874-876 ◽  
Author(s):  
CLAUDE P. CHAMPAGNE ◽  
NANCY J. GARDNER ◽  
JULIE FONTAINE ◽  
JACQUES RICHARD
Keyword(s):  
Raw Milk ◽  
Plate Count ◽  
Bacterial Populations ◽  
Filter Technique ◽  
Milk Samples ◽  
Standard Plate ◽  
Plate Counts ◽  
Direct Epifluorescent Filter Technique ◽  
Triton X

The results from a shortened procedure for the direct epifluorescent filter technique (DEFT) determination of viable bacterial populations in raw milk were compared to standard plate counts. Shortening the prefiltration trypsin-Triton X-100 incubation period from 10 to 3 min enabled the completion of the analysis within 20 min. The short DEFT method results had a correlation coefficient (r) of 0.81 with plate counts. With respect to precision, the average difference between values of duplicate plate count analyses was 0.16 log units; that of the short DEFT was 0.14 log units. The slopes of the regressions equations were less than 1, indicating that a direct correlation is not achieved. Short DEFT values were 0.17 log units higher than those of plate counts on milk samples containing less than 10,000 CFU/ml. For milk samples containing counts over 10,000 CFU/ml, short DEFT values averaged only 0.05 log units above plate count readings. Daily preparation of the stain appears unnecessary since acridine orange solutions stored for up to 2 days at 4°C did not produce results significantly (P > 0.05) different from those obtained with fresh solutions. The short DEFT method has potential for the assessment of the bacteriological quality of raw milk in tanker deliveries.

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.

Temperature Equilibration Times of Plate Count Agar and a Comparison of 50 Versus 45 C for Recovery of Raw-Milk Bacteria1

1975 ◽  
Vol 38 (6) ◽  
pp. 319-322 ◽  
Author(s):  
C. N. HUHTANEN ◽  
A. R. BRAZIS ◽  
W. L. ARLEDGE ◽  
C. B. DONNELLY ◽  
R. E. GINN ◽  
...  
Keyword(s):  
Raw Milk ◽  
Plate Count ◽  
Equilibration Time ◽  
Standard Methods ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Plate Count Agar ◽  
Standard Plate ◽  
Time Required ◽  
Tempering Time

Sixty raw milk samples were plated using “Standard Methods” agar tempered to 45 or 50 ± 1 C. The standard plate count was significantly lower with the agar at 50 C. Tempering time (to 44–46 C) of a flask of agar in a water bath was about 5–10 min longer than that of a comparable flask of water. Time required to reach the desired temperature depended upon the volume of agar in the flasks, the number of flasks, and the volume of the water in the bath. Up to an hour of equilibration time may be necessary for newly autoclaved agar to reach the recommended temperature (44–46 C). Insufficient tempering time might cause an excessively high plating agar temperature which might cause a reduction in bacterial counts, especially of a heat sensitive psychrotrophic bacterium.

THE EFFECT OF PLATE INCUBATION TEMPERATURES ON COUNTS OF SODIUM DESOXYCHOLATE-TOLERANT BACTERIA

1970 ◽  
Vol 33 (10) ◽  
pp. 442-444 ◽  
Author(s):  
G. Blankenagel
Keyword(s):  
Milk Samples ◽  
Bulk Milk ◽  
Standard Plate ◽  
Plate Counts ◽  
Incubation Temperatures

Farm bulk milk samples from 54 producers were analyzed for Standard Plate Counts (SPC), thermoduric counts, and counts of bacteria that can tolerate 0.5% sodium desoxycholate (SDC). For the latter test, plates were incubated at 21, 25, 28, and 32 C for 48 hr. More milk samples had maximum counts at 25 C than at any other temperature used, whereas 32 C yielded the lowest number of colonies per plate. Median counts were 250/ml at 21, 290/ml at 25, 275/ml at 28, and 160/ml at 32 C.

Effect of Agitation on Bacterial Aggregates in Pure Cultures and Raw Milk

1983 ◽  
Vol 46 (8) ◽  
pp. 681-685 ◽  
Author(s):  
ROBYN E. O'CONNOR ◽  
K. N. EWINGS ◽  
NEIL W. HOLLYWOOD
Keyword(s):  
Raw Milk ◽  
Mechanical Agitation ◽  
Filter Technique ◽  
Milk Samples ◽  
Pure Cultures ◽  
Plate Counts ◽  
Bacterial Aggregates ◽  
Direct Epifluorescent Filter Technique ◽  
Clump Size

A comparison of the effects of various mechanical agitation treatments on bacterial aggregates was performed on 8 pure cultures and 27 raw milk samples. Although both syringing and blending produced significant increases in total counts and psychrotroph counts, blending for 2 min gave the greatest increase in count. Use of the direct epifluorescent filter technique (DEFT) confirmed that syringing and blending reduced bacterial clump size to approximately 2 cells. These agitation treatments markedly improved the correlation between DEFT counts and plate counts.

AN EVALUATION OF SIMPLIFIED METHODS FOR DETERMINING VIABLE COUNTS OF RAW MILK

1960 ◽  
Vol 23 (9) ◽  
pp. 275-277 ◽  
Author(s):  
C. B. Donnelly ◽  
L. A. Black ◽  
K. H. Lewis
Keyword(s):  
Rapid Method ◽  
Raw Milk ◽  
Accurate Method ◽  
Bacterial Counts ◽  
Milk Samples ◽  
Standard Plate ◽  
Plate Counts ◽  
Oval Tube

When statistically analyzed, the results of comparative, examinations of raw milk samples revealed that bacterial counts by oval tube and microplate methods were essentially equivalent to standard plate counts. The oval tube provides an economical and accurate method for determining the count of producers' milk and may be used in the laboratory or on the platform. The microplate provides an equally accurate but more rapid method than either the oval tube or standard plate since counts be obtained in 20 hours.

scholarly journals Study on the Level of Aflatoxin M1 Contamination in Raw and Processed Milk Marketed in Kathmandu Valley

2014 ◽  
Vol 7 ◽  
pp. 52-56 ◽  
Author(s):  
Pratap Kafle ◽  
Damodar Sedai ◽  
Krishna Prasad Rai ◽  
Bishow Bandhu Pokharel
Keyword(s):  
Thin Layer ◽  
Thin Layer Chromatography ◽  
Raw Milk ◽  
Aflatoxin M1 ◽  
Kathmandu Valley ◽  
Milk Samples ◽  
Residual Level ◽  
Maximum Tolerance ◽  
The Difference ◽  
Layer Chromatography

Aflatoxin M1 (AFM1) is the principal hydroxylated AFB1 metabolite mainly present in milk. In this study the levels of Aflatoxin M1 (AFM1) in Raw and Pasteurized milk marketed in Kathmandu valley was estimated. Altogether 32 milk samples (Raw 16, Pasteurized 16) obtained from different areas of Kathmandu valley were analysed for AFM1 by Thin Layer Chromatography. The milk samples were analyzed according to the official AOAC methods, which included extraction of toxin using chloroform, clearing by silica gel column chromatography, qualitative analysis by Thin Layer Chromatography and quantification by Visual comparison of the spots. AFM1 was found in 14 (43.75%) of milk samples examined. The levels of AFM1 in 7 (21.87%) samples were higher than the maximum tolerance limit (0.05 µg/l) accepted by some European countries while none of the samples exceeded the prescribed limit of US regulations. The mean concentration of AFM1 was higher in Raw milk (0.030 ± 0.042 µg/l) compared to pasteurized (0.022 ± 0.039) but the difference was not statistically significant (p>0.05). This finding reflects that milk marketed in Kathmandu valley contains residual level of Aflatoxin M1 and pose public health risk. Therefore, milk and milk products have to be screened for AFM1 contamination periodically. DOI: http://dx.doi.org/10.3126/jfstn.v7i0.10598   J. Food Sci. Technol. Nepal, Vol. 7 (52-56), 2012  

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