INFLUENCE OF REFRIGERATED STORAGE ON DYE REDUCTION TIME OF MILKS

1952 ◽  
Vol 15 (1) ◽  
pp. 8-12 ◽  
Author(s):  
C. K. Johns
Keyword(s):  
Methylene Blue ◽  
Close Agreement ◽  
Raw Milk ◽  
Refrigerated Storage ◽  
Methylene Blue Reduction ◽  
Dye Reduction ◽  
Standard Plate ◽  
Plate Counts ◽  
The Difference ◽  
Better Than

Working with 100 weigh-can samples from 5 dairies it was found that icing for even 2 hours slightly retarded reduction of methylene blue; after 23 hours the effect was somewhat greater when the dye was present, but not when it was added just before incubation. With resazurin, on the other hand, there was better agreement when the dye was present during overnight storage. In no instance was the difference statistically significant. Methylene blue reduction times were in surprisingly close agreement with standard plate counts on the raw milk, while the correlation between reduction times (raw) and plate counts after laboratory pasteurization was better than was expected.

SOME FACTORS AFFECTING THE CORRELATION OF METHYLENE BLUE REDUCTION TIMES AND STANDARD PLATE COUNTS OF RAW MILK

1966 ◽  
Vol 29 (8) ◽  
pp. 255-259
Author(s):  
A. Richard Brazis ◽  
L. A. Black
Keyword(s):  
Methylene Blue ◽  
Standard Procedure ◽  
Raw Milk ◽  
Bacterial Counts ◽  
Factors Affecting ◽  
Methylene Blue Reduction ◽  
Standard Plate ◽  
Plate Counts

Summary Standard plate and psychrophilic bacterial counts, on 312 samples of milk collected from farm bulk tanks and milk cans, were compared with methylene blue reduction times using the standard procedure or preliminary incubation of samples at 55 F for 18 hr prior to testing. When psychrophilic bacterial counts were less than 100,000/ml, according to standard plate counts a high proportion of methylene blue reduction times were properly classified. However, psychrophilic bacterial counts greater than 100,000/ml did not significantly decrease reduction times, thus a high proportion of such milks was not properly classified by methylene blue reduction times. The proportion of misclassification of samples having standard plate counts in excess of 200,000/ml and methylene blue reduction times of 5 and 6 hr was determined.

386. Variations in morphology of Streptococcus lactis when grown in raw and heated milk

1949 ◽  
Vol 16 (2) ◽  
pp. 161-166 ◽  
Author(s):  
C. S. Morris ◽  
M. A. Edwards
Keyword(s):  
Methylene Blue ◽  
Incubation Period ◽  
Incubation Time ◽  
Raw Milk ◽  
Morphological Characters ◽  
Streptococcus Lactis ◽  
Heated Milk ◽  
Methylene Blue Reduction ◽  
The Difference ◽  
By Products

1. Streptococcus lactis cultures were found to vary considerably in their morphological characters when grown in raw and heated milk.2. This variation in morphology was found to be the main cause for the difference in colony counts between inoculated raw milk and milk heated to 70° C. for 1 hr. over a 6 hr. incubation period at 37° C.3. Similar T.M.C.'S on inoculated raw and heated milk during incubation at 37° C. explained why the methylene-blue reduction times were the same.4. It is thought that denaturation of protein may be responsible for the production of short chains in heated milk.5. The by-products of growth of Str. lactis are responsible for the production of short chains in raw milk after a long incubation time at 37° C.

Assessment of different selective agar media for enumeration and isolation ofListeriafrom dairy products

1988 ◽  
Vol 55 (4) ◽  
pp. 579-583 ◽  
Author(s):  
Lucas Dominguez ◽  
José Francisco Fernández ◽  
Victor Briones ◽  
José Luis Blanco ◽  
Guillermo Suárez
Keyword(s):  
Dairy Products ◽  
Agar Medium ◽  
Raw Milk ◽  
Superior Performance ◽  
Direct Plating ◽  
Selective Agar ◽  
Natural Microflora ◽  
Agar Media ◽  
The Difference ◽  
Better Than

SummaryDifferent selective agar media were compared for the recovery and isolation of five species ofListeriafrom raw milk and cheese. The selective media examined were Beerens medium, MacBride medium and that described by Dominguezet al.(1984) with 6 mg/1 acriflavine, listeria selective agar medium (LSAM), and LSAM with 12 mg/1 acriflavine (LSAM × 2A); a non-selective yeast glucose Lemco agar was included for comparison. When the difference between listeria and the natural microflora of raw milk and cheese was 102cfu/ml, listeria could be isolated by direct plating on all media tested. When it was lower than 103–104cfu/ml, listeria were isolated by direct plating only on LSAM and LSAM × 2A. When the difference was greater than 104cfu/ml, a previous enrichment was necessary to isolate them. LSAM and LSAM × 2A media performed better than the other media tested for isolating listeria by direct plating and improved their isolation from dairy products. This superior performance was evaluated by the ability of these media to support colony formation of different species ofListeriatested, the easy recognition of these colonies from those formed by other microorganisms and by their capacity to inhibit the natural microflora of these foods.

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.

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.

scholarly journals A Cheap and Efficient Medium for the Plate Count of Milk

1942 ◽  
Vol 42 (2) ◽  
pp. 218-223
Author(s):  
H. Barkworth ◽  
J. G. Davis
Keyword(s):  
Methylene Blue ◽  
Bacterial Count ◽  
Colony Count ◽  
Considerable Importance ◽  
Plate Count ◽  
Pasteurized Milk ◽  
Inadequate Information ◽  
Dye Reduction ◽  
Plate Counts ◽  
Official Recognition

The plate count is no longer considered the only test for the bacterial count of milk. There has recently been a tendency for the methylene-blue, or even the recently developed resazurin test, to displace the colony count as a measure of hygienic quality. Many workers, however, after experience with the dye reduction tests, have returned to the plate count, especially for advisory work, and consider that the new simple tests give inadequate information. Moreover, the plate count is still considered the best test for pasteurized milk. The questions of cost and availability of medium constituents, therefore, assume considerable importance in wartime.Two media (Min. Health, 1937; Min. Agric. 1934) have received official recognition in England for routine plate counts of milk. Both media (yeastrel agar and milk agar) contain 0·5% peptone, so that a considerable amount can be used if a large number of samples is tested. A shortage of peptone has already been experienced and the price has increased by over 100%. Experiments were therefore undertaken to find an alternative satisfactory medium containing less peptone.

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.

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