Pyruvate as an Indicator of Quality in Grading Nonfat Dry Milk1

1982 ◽  
Vol 45 (6) ◽  
pp. 561-565 ◽  
Author(s):  
R. T. MARSHALL ◽  
Y. H. LEE ◽  
B. L. O'BRIEN ◽  
W. A. MOATS
Keyword(s):  
Geometric Mean ◽  
Regression Line ◽  
Skim Milk ◽  
Plate Count ◽  
Department Of Agriculture ◽  
Standard Plate Count ◽  
Geometric Average ◽  
Dry Milk ◽  
Standard Plate ◽  
Microscopic Count

Samples of skim milk and nonfat dry milk (NDM) made from it were collected, paired and tested for pyruvate concentration, [P], and Direct Microscopic count (DMC). The skim milk was tested for Standard Plate Count (SPC) and Psychrotrophic Plate Count (PPC). The geometric average DMC of skim milk was more than three times higher than that of the paired NDM samples. However, [P] of NDM was not significantly different from that of the skim milk. Although [P] of skim milk was poorly correlated with SPC and PPC, r = .31 and .26, respectively, it was relatively well correlated with DMC, r = .64. Data were widely dispersed around the regression line when [P] was ≤ 4.0 mg/L. However, [P] increased rapidly when DMCs were > 106/ml. A limit of 10 mg/L of [P] in NDM reconstituted 1:9 was chosen to represent the current U.S. Department of Agriculture Standard for DMC in NDM. This limit failed to classify about 10% of the samples correctly, assuming that each geometric mean DMC was correct. However, the probability that samples meeting the DMC standard would be rejected by the pyruvate test was quite low and the probability was moderate that samples which would be acceptable by the pyruvate test would be rejected by the DMC. For the latter, 28% of the samples having DMCs of ≥ 107/ml contained < 10 mg/L of pyruvate. No sample having ≥ 10 mg/L of pyruvate had a DMC of ≤ 107/ml. Pyruvate concentration in NDM did not change during storage at 5 or 32°C for 90 days.

Pyruvate in Producer and Commingled Manufacturing Grade Milk

1982 ◽  
Vol 45 (13) ◽  
pp. 1236-1241 ◽  
Author(s):  
R. T. MARSHALL ◽  
B. L. O'BRIEN ◽  
Y. H. LEE ◽  
W. A. MOATS
Keyword(s):  
False Negative ◽  
Skim Milk ◽  
Plate Count ◽  
Negative Type ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Standard Plate ◽  
Microscopic Count ◽  
Highly Correlated

The automated test for pyruvate concentration, [P], was evaluated as a substitute for the direct microscopic count (DMC) in determining quality of manufacturing grade milk. Samples of manufacturing grade milk from producers and tank trucks as well as skim milk were collected at a large milk drying plant. Each sample was tested immediately for standard plate count (SPC), psychrotrophic plate count (PPC) and DMC. Portions of milk were heated to 85°C for 10 min to stabilize [P] before being returned to the laboratory for analysis of initial pyruvate concentration, [IP]. Unheated samples stored at 4°C were analyzed for [P] and DMC daily for up to 120 h. [IP] was a good indicator of PPC in milk from individual producers (r=0.81). However, [IP] was not highly correlated (r=0.26) with PPC in skim milk samples which were characteristically high in SPC and homogeneous in PPC. With skim milk, [IP] was more highly and significantly correlated with initial DMC (r=0.61) than with initial SPC (r=0.31) or initial PPC (r=0.26). [IP] was a good indicator of [P] in stored fluid samples until counts exceeded about 107/ml. Initial DMC and initial PPC were about equally correlated with [P] determined at 24-h intervals, and the initial DMC was a reasonably good indicator of DMC determined at 24-h intervals. Using 6.5 mg of pyruvate/L to represent bacterial counts of 3 × 106/ml by the three methods tested, the pyruvate test correctly classified 91% of 57 samples of producer milk based on PPC, 88% based on SPC and 82% based on DMC. Most of the error was of the false-negative type in which samples with high counts had less than 6.5 mg of pyruvate/L. This was probably because some bacteria catabolize pyruvate once their numbers exceed 107/ml.

Impedance Measurements in Raw Milk as an Alternative to the Standard Plate Count1

1982 ◽  
Vol 45 (1) ◽  
pp. 4-7 ◽  
Author(s):  
S. GNAN ◽  
L. O. LUEDECKE
Keyword(s):  
Yeast Extract ◽  
Geometric Mean ◽  
Raw Milk ◽  
Plate Count ◽  
Impedance Method ◽  
Microbial Count ◽  
Specific Detection ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Standard Plate

Electrical impedance, using the Bactometer 32, was evaluated as an alternative method to the Standard Plate Count (SPC) to determine the initial microbial count of raw milk samples. The raw milk samples were obtained from farm bulk tanks on commercial dairy farms. Analyses were started within 24–36 h after collection. The impedance method was used to evaluate the samples as raw milk, raw milk plus yeast extract, raw milk given preliminary incubation (18 h at 13 C) or raw milk given preliminary incubation plus yeast extract. The yeast extract (1% final concentration) was added after the milk was placed in the module wells. The geometric mean SPC of each of these four groups was 4.51, 4.37, 4.96 and 5.14, and the corresponding mean detection times with Bactometer 32 were 10.13, 8.80, 8.28 and 6.11 h, respectively. The correlation coefficient of detection time to SPC was −0.77, −0.88, −0.78 and −0.79, respectively, for the four sample groups. When specific detection cut-off times (approximately 7 h) were selected and a maximum SPC of 100,000 CFU/ml was selected, 85.2%, 97.2%, 81.0% and 83.6%ofthe samples in the above four groups were correctly classified.

MANUFACTURING MILK QUALITY: A RE-EVALUATION

1971 ◽  
Vol 34 (5) ◽  
pp. 249-255 ◽  
Author(s):  
William S. LaGrange
Keyword(s):  
Milk Quality ◽  
Plate Count ◽  
Dairy Farmers ◽  
High Count ◽  
Psychrotrophic Bacteria ◽  
Standard Plate Count ◽  
Processing Plants ◽  
Standard Plate ◽  
Plate Counts ◽  
Microscopic Count

The bacteriological quality of manufacturing-grade milk is very similar to that marketed a decade earlier when bulk tanks first came into general use. Milk grading programs usually relied on reduction tests. These tests indicated that most milk supplies were good quality. Based on the Standard Plate Count, data is presented that show approximately one-third of the samples tested, in 1969–70 and in 1957–59, exhibit counts <200,000/ml. Considerable quantities of milk, received at processing plants have plate counts exceeding 1,000,000/ml. Dairy farmers learned they could substitute cooling for cleaning because psychrotrophic bacteria predominated the microflora of most high count bulk milk. These bacteria do not readily reduce resazurin and methylene blue. Psychrotrophs also tend to grow in clumps preventing an accurate evaluation of milk quality using the Direct Microscopic Count (DMC). USDA uses the DMC to test check manufacturing plant's milk supplies. Laboratories are recognizing the value of plating procedures, including the Plate Loop Count, to determine milk quality. Manufacturing-grade milk must be evaluated with a plating procedure before progress can be made in milk quality improvement. One grade of milk is far from being a reality if present levels of manufacturing-grade milk quality are considered.

An Update Survey of Bulk Tank Milk Quality in Vermont

1991 ◽  
Vol 54 (7) ◽  
pp. 549-553 ◽  
Author(s):  
JOHN J. GOLDBERG ◽  
JOSEPH W. PANKEY ◽  
PEGGY A. DRECHSLER ◽  
PATRICIA A. MURDOUGH ◽  
DIANTHA B. HOWARD
Keyword(s):  
Somatic Cell ◽  
Research Laboratory ◽  
Somatic Cell Count ◽  
Geometric Mean ◽  
Arithmetic Mean ◽  
Plate Count ◽  
Bulk Tank Milk ◽  
Standard Plate Count ◽  
Standard Plate ◽  
Bulk Tank

Quality of Vermont bulk tank milk was first surveyed in 1985 as part of a statewide milk quality enhancement program. In a second survey conducted in 1990, bulk tank milk from 1,971 farms was sampled and tested for standard plate count, bacterial type and species distribution, and somatic cell count. Test results from 1,203 duplicate bulk tank milk samples were compared between five Vermont milk processors and the University of Vermont Quality Milk Research Laboratory. Arithmetic mean standard plate count conducted by processors was 2.3 × 104 CFU/ml in 1990 compared with 3.0 × 104 CFU/ml in 1985 (Geometric mean went from 1.3 × 104 CFU/ml in 1985 to 1.1 × 104 CFU/ml in 1990). Trypticase blood-esculin agar was used at the Quality Milk Research Laboratory to determine distribution of bacteria types and species. Comparison of results with a 1985 survey appeared to demonstrate a reduction in the percentage of farms with Streptococcus agalactiae from 47% to 32%. Frequency of other organisms increased with the majority being environmental organisms. Arithmetic mean total raw bacteria count on blood agar was 1.9 × 104 CFU/ml. Correlation between standard plate count and blood agar raw bacteria count was low. Arithmetic mean somatic cell count appeared to decline from 5.4 × 105 cells/ml in 1985 to 3.4 × 105 cells/ml in 1990 (Geometric mean went from 4.1 × 105 cells/ml in 1985 to 2.9 × 105 cells/ml in 1990). Correlation between somatic cell counts conducted by milk processors and the Quality Milk Research Laboratory was high.

Estimation of Potential Shelf-life of Pasteurized Fluid Milk Utilizing Bacterial Numbers and Metabolites

1985 ◽  
Vol 48 (8) ◽  
pp. 663-667 ◽  
Author(s):  
J. R. BISHOP ◽  
C. H. WHITE
Keyword(s):  
Shelf Life ◽  
Skim Milk ◽  
Daily Basis ◽  
Prediction Equation ◽  
Plate Count ◽  
Regression Equations ◽  
Psychrotrophic Bacteria ◽  
Standard Plate Count ◽  
Standard Plate ◽  
Fluid Milk

A study was conducted on use of bacterial numbers and their metabolites, and any possible interaction thereof, as estimators of the potential shelf-life of pasteurized fluid milk. Whole and skim milk samples were obtained on the day of processing. Samples of each milk were inoculated in duplicate with 0, 1,000, or 100,000 bacteria/ml with a pure strain of Pseudomonas fluorescens P27. Samples, stored at 7°C, were analyzed for microbiological and bioichemical parameters every 5 d for up to 20 d, with organoleptic evaluations conducted on a daily basis. On days of analysis, each sample was subjected to various preliminary incubations. Bacterial enumerations conducted were psychrotrophic bacteria count, standard plate count, gram-negative bacteria count, and modified psychrotrophic bacteria count. Lipopolysaccharide (endotoxin) concentrations, degree of proteolysis and impedance detection were also determined. All bacterial enumerations and proteolysis were significantly related to potential shelf-life of pasteurized fluid milk (whole, skim, and combined) but were of little predictive value. Endotoxin concentration and impedance detection were highly significantly related to shelf-life, and provided predictive regression equations. Using combined data from whole and skim milk, impedance detection resulted in the preferred prediction equation suitable for pasteurized fluid milks.

EVALUATION OF PRODUCTION CONDITIONS OF MANUFACTURING-GRADE RAW MILK BY FIELDMEN RATINGS AND BY BACTERIAL TESTS

1971 ◽  
Vol 34 (4) ◽  
pp. 200-203 ◽  
Author(s):  
Roger Dabbah ◽  
W. A. Moats ◽  
J. C. Olson
Keyword(s):  
Correlation Coefficients ◽  
Raw Milk ◽  
Plate Count ◽  
Standard Plate Count ◽  
Reduction Test ◽  
Sanitary Condition ◽  
Methylene Blue Reduction ◽  
Standard Plate ◽  
Microscopic Count ◽  
Production Conditions

Standard microbiological tests, Standard Plate Count, direct microscopic count, methylene blue reduction test, and several variations of the resazurin reduction test were correlated with fieldmen's ratings of sanitary condition of milking area, milk house, and milking utensils. Correlation coefficients were low, in general, approximately 0.2. The effect of different production facilities and practices on these correlations was variable. Results suggest that bacterial tests and fieldmen's inspection be used concurrently since they appear to measure different sanitary factors on the producing farms.

COMPARISON OF METHODS FOR GRADING MILK INTENDED FOR MANUFACTURING PURPOSES1,2

1967 ◽  
Vol 30 (3) ◽  
pp. 71-76 ◽  
Author(s):  
Roger Dabbah ◽  
Sita Ramayya Tatini ◽  
J. C. Olson
Keyword(s):  
Geographical Location ◽  
The United States ◽  
Plate Count ◽  
United States Department ◽  
Department Of Agriculture ◽  
Standard Plate Count ◽  
Class 1 ◽  
Standard Plate ◽  
Bulk Tank ◽  
Level Of Significance

Summary Samples of milk intended for manufacturing purposes were obtained once each season from randomly selected dairy farms in three widely separated geographical locations. Samples (3873) were analyzed by standard plate count (SPC-32 C), direct microscopic clump count (DMCC), methylene blue (MBRT) and resazurin (RRT), (5P 7/4) test. Correlations for SPC vs. DMCC, MBRT, and RRT were r = 0.78, −0.82 and −0.79, respectively; DMCC vs. MBRT, RRT, r = −0.75 and −0.68, respectively; MBRT vs. RRT, r = 0.86. Prediction of DMCC, MBRT, and RRT on the basis of their regressions with SPC Were influenced significantly (99% level of significance) by the geographical source of samples, the type of milk handling on the farm (can or farm bulk tank) and season. On the basis of equivalents (determined by regression) between classifying tests, new standards were developed. The percentage of samples classed the same by the four methods using these new calculated classifications or the classification recommended by the United States Department of Agriculture (USDA) was approximately 50% of all samples. Agreement between the four methods of classifying samples was not close enough to warrant the interchangeable use of the four tests. Results from calculated classifications varied considerably with geographical location and with the method of handling milk on the farm. Although the use of calculated classifications would give better agreement among the four methods when applied to the supplies from which they were derived, multiplicity of tests methods, their application and interpretation would cause much confusion. Use of the RRT with a 5P 7/4 Munsell color end-point with separate procedures, one for can supplies (RRT: > 2 1/2, ≤ 2 1/2, and ≤ 1 1/2 hr for Class 1, 2, and 3, respectively) and one for farm bulk tank supplies (RRT: > 3 1/2, ≤ 3 1/2, and ≤ 2 1/2 for Class 1, 2, and 3, respectively) resulted in grading milk, intended for manufacturing purposes, more uniformly than either use of the four classification methods interchangeably or even use of a single RRT standard based on all samples regardless of type of milk handling on the farm (can or bulk tanks).

Evaluation of the 3M™ Petrifilm™ Rapid Aerobic Count Plate for the Enumeration of Aerobic Bacteria: Collaborative Study, First Action 2015.13

2016 ◽  
Vol 99 (3) ◽  
pp. 664-675
Author(s):  
Patrick Bird ◽  
Jonathan Flannery ◽  
Erin Crowley ◽  
James Agin ◽  
David Goins ◽  
...  
Keyword(s):  
Collaborative Study ◽  
Skim Milk ◽  
Plate Count ◽  
Aerobic Bacteria ◽  
Contamination Level ◽  
Standard Plate Count ◽  
Dual Sensor ◽  
Standard Plate ◽  
Aerobic Plate Count ◽  
Contamination Levels

Abstract The 3M™ Petrifilm™ Rapid Aerobic Count (RAC) Plate is a sample-ready culture medium system containing dual-sensor indicator technology for the rapid quantification of aerobic bacteria in food products. The 3M Petrifilm RAC Plate was compared to the U.S. Food and Drug Administration Bacteriological Analytical Manual (FDA BAM) Chapter 3 (Aerobic Plate Count) for the enumeration of aerobic bacteria in raw easy-peel shrimp and the Standard Methods for the Examination of Dairy Products (SMEDP) Chapter 6 (Standard Plate Count Method) for the enumeration of aerobic bacteria in pasteurized skim milk and instant nonfat dry milk (instant NFDM). The 3M Petrifilm RAC Plate was evaluated using a paired study design in a multilaboratory collaborative study following current AOAC validation guidelines. Three target contamination levels (low, 10–100 CFU/g; medium, 100–1000 CFU/g; and high 1000–10 000 CFU/g) were evaluated for naturally occurring aerobic microflora for each matrix. For raw easy-peel shrimp, duplicate 3M Petrifilm RAC Plates were enumerated after 24 ± 2 h incubation at both 32 and 35°C. Pasteurized skim milk 3M Petrifilm RAC Plates were enumerated after 24 ± 2 h incubation at 32°C, and instant NFDM 3M Petrifilm RAC Plates were enumerated after 48 ± 3 h incubation at 32°C. No statistical difference was observed between 3M Petrifilm RAC Plate and FDA BAM or SMEDP reference methods for each contamination level.

CORRELATION BETWEEN STANDARD PLATE COUNT AND FOUR DIRECT MICROSCOPIC COUNT PROCEDURES FOR MILK

1966 ◽  
Vol 29 (12) ◽  
pp. 366-371 ◽  
Author(s):  
Roger Dabbah ◽  
W. A. Moats
Keyword(s):  
Acetic Acid ◽  
Toluidine Blue ◽  
Periodic Acid ◽  
Plate Count ◽  
Staining Procedure ◽  
Standard Plate Count ◽  
Bisulfite Treatment ◽  
Geometrical Pattern ◽  
Standard Plate ◽  
Microscopic Count

Summary The standard plate count (SPC-32 C) and the direct microscopic count (DMC) of samples of commercially pasteurized milk inoculated with pure cultures of actively growing (18–24 hr growth) bacteria commonly found in milk were compared. Four staining procedures for DMC were used: (a) Levowitz-Weber's methylene blue stain; (b) a modified Levowitz-Weber stain incorporating basic fuchsin; (c) alcoholic-acetic acid fixation followed by periodic acid-bisulfite treatment and staining with pH4 toluidine blue; and (d) alcoholic-acetic acid fixation and staining with pH4 toluidine blue. Counting was standardized by the use of a geometrical pattern. Correlations between SPC and each DMC procedure, or among the DMC procedures were little influenced by the number of microscopic fields counted, their location on the smear or the definition of “clumping” used. Correlations were influenced by the type of bacterial culture inoculated in milk and by the staining procedure. Precision of DMC was shown to be independent from the staining procedure, but varied directly with the number of cells per field and inversely with the square root of the number of fields counted.

Bioluminescence: A Rapid Indicator of Escherichia Coli O157:H7 in Selected Yogurt and Cheese Varieties

1997 ◽  
Vol 60 (8) ◽  
pp. 891-897 ◽  
Author(s):  
L. M. HUDSON ◽  
J. CHEN ◽  
A. R. HILL ◽  
M. W. GRIFFITHS
Keyword(s):  
Escherichia Coli ◽  
Enterohemorrhagic Escherichia Coli ◽  
Cottage Cheese ◽  
Plate Count ◽  
Escherichia Coli O157 ◽  
Potential Hazard ◽  
Growth And Survival ◽  
E Coli ◽  
Standard Plate Count ◽  
Standard Plate

Outbreaks of enterohemorrhagic Escherichia coli O157:H7 have been commonly associated with products derived from ground beef, but recently the organism has been implicated as the causative agent in outbreaks involving yogurt and cheese. This finding has raised concern about the potential for its growth and survival in fermented dairy products. A bioluminescent strain of E. coli O157:H7 was used to determine postprocessing survival in yogurt with live cultures at pH 4.17, 4.39, and 4.47 stored at 4 and 10°C. In addition, survival of E. coli O157:H7 was monitored during the manufacture of Cottage, Colby, Romano, and Feta cheeses. Results indicated survival for 8 and 5 days at 4 and 10°C respectively in yogurt at pH 4.17, 17 and 15 days at 4 and 10°C respectively in yogurt at pH 4.39, and 17days at both 4 and 10°C in yogurt at pH 4.47. E. coli O157:H7 did not survive cooking procedures at 56°C in Cottage cheese. However, the pathogen survived for 27, 30, and 27 days in Colby, Romano, and Feta cheeses respectively. A high correlation of r2 > 0.89 was obtained between counts of bioluminescenct colonies and standard plate count for all yogurt and cheese varieties, indicating that bioluminescence was a sensitive and rapid indicator of cellular viability for E. coli O157:H7. Survival of the pathogen, as indicated by this method, is possible in highly acidic environments even at refrigeration temperatures. This poses a potential hazard should postprocessing contamination occur.

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