Rapid Impedimetric Method for Determining the Potential Shelf-Life of Pasteurized Whole Milk

1984 ◽  
Vol 47 (6) ◽  
pp. 471-475 ◽  
Author(s):  
J. R. BISHOP ◽  
C. H. WHITE ◽  
R. FIRSTENBERG-EDEN
Keyword(s):  
Shelf Life ◽  
Correlation Coefficients ◽  
Plate Count ◽  
Impedance Method ◽  
Organoleptic Evaluation ◽  
Evaluation Standard ◽  
Psychrotrophic Bacteria ◽  
Standard Plate Count ◽  
Significant Relationships ◽  
Whole Milk

Potential shelf-life of 100 pasteurized whole milk samples, obtained from retail outlets and from dairy processors, was investigated. Parameters studied were: organoleptic evaluation, Standard Plate Count (SPC), psychrotrophic bacteria count (PBC), modified psychrotrophic bacteria count (mPBC), Moseley test (MSPC), and impedance detection time (IDT) at 18 and 21°C. Correlation coefficients were obtained for all possible data combinations in an attempt to detect significant relationships between the parameters studied and the true shelf-life of the product. None of the direct counts (SPC, PBC, and mPBC) correlated well enough with shelf-life to allow shelf-life prediction. Moseley test (MSPC) appeared to possess an adequate relationship to shelf-life with a correlation coefficient at −0.84. IDT 21°C and IDT 18°C proved to have the most significant relationships to shelf-life with correlation coefficients of 0.88 and 0.87, respectively. Therefore, the impedance method had three advantages over the Moseley test: (a) it was a better predictor of shelf-life, (b) it was less labor intensive, and (c) it required only 1–2 d, as opposed to 7–9 d to complete.

Evaluation of a Rapid Impedimetric Method for Determining the Keeping Quality of Milk

1982 ◽  
Vol 45 (13) ◽  
pp. 1221-1226 ◽  
Author(s):  
S. B. MARTINS ◽  
S. HODAPP ◽  
S. W. DUFOUR ◽  
S. J. KRAEGER
Keyword(s):  
Shelf Life ◽  
Correlation Coefficients ◽  
Sample Volume ◽  
Plate Count ◽  
Impedance Method ◽  
Detection Time ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Standard Plate ◽  
Quality Of Milk

Shelf-life of 151 pasteurized milk samples was recorded and correlation coefficients calculated using various microbiological factors: standard plate count (SPC), psychrotrophic plate count (PPC), coliform count (CC), and the impedance response detection time (DT) with incubation at both 21 and 32°C. These data were obtained for milk samples on the day of pasteurization as well as 4 and 8 d thereafter. Various treatments (media, dilution factors, temperature and sample volume) were compared. Of the SPC, PPC, CC and DT taken on the day of pasteurization, only the DT achieved a significant correlation with shelf-life. A correlation coefficient of 0.55 was obtained for one treatment applied to 61 samples and correlation coefficients of 0.28 to 0.32 were obtained for several other treatments applied to the entire 151 samples. Values as large as these could occur by chance in uncorrelated data with p<0.0005. Thus, of the total 61 samples, 80% were correctly classified by the impedance detection time test. It is concluded that for prediction of shelf-life on the day of pasteurization, the impedance method is superior to the SPC and the PPC. In addition, the impedance method is more rapid, i.e., 14 h vs.2 d for the SPC and 10 d for the PPC.

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.

Estimation of Potential Shelf Life of Cottage Cheese Utilizing Bacterial Numbers and Metabolites

1985 ◽  
Vol 48 (12) ◽  
pp. 1054-1057 ◽  
Author(s):  
J. R. BISHOP ◽  
C. H. WHITE
Keyword(s):  
Shelf Life ◽  
Correlation Coefficients ◽  
Daily Basis ◽  
Prediction Equation ◽  
Detection Methods ◽  
Cottage Cheese ◽  
Plate Count ◽  
Psychrotrophic Bacteria ◽  
Cheese Curd ◽  
Aerobic Plate Count

A study was conducted to investigate the use of bacterial numbers and their metabolites as estimators of the potential shelf life of cottage cheese. Dry cottage cheese curd and cream dressing were obtained on the day of processing. Portions of the cream dressing were inoculated with Pseudomonas fluorescens P27 to result in approximate levels of 0, 1,000 and 100,000 bacteria per g in finished cottage cheese after combining the curd and cream. Samples, stored at 7°C, were sensorially evaluated on a daily basis and analyzed every 7 d for up to 35 d. On days of analysis each sample was subjected to preliminary incubation (PI) as follows: none, 21°C for 7 h, 21°C for 14 h, 13°C for 18 h and 18°C for 18 h. For each PI, samples were enumerated by aerobic plate count, modified psychrotrophic bacteria count and gram-negative (CVT) count. Samples were enumerated for the standard psychrotrophic bacteria count without PI. Samples were also exposed to 18°C for 18 h PI in plate count broth for impedance detection measurements. Endotoxin (lipopolysaccharide) concentration and proteolysis were determined by the Limulus amebocyte lysate assay and the o-phthaldialdehyde method, respectively. Bacterial enumerations proved to be of little estimative value as the highest correlation coefficient obtained was −0.61. Endotoxin, proteolysis and impedance detection methods resulted in high correlation coefficients as related to potential shelf life of cottage cheese, with values of −0.81, −0.87 and −0.90, respectively. A prediction equation was formulated from the data.

Estimation of Potential Shelf-life of Pasteurized Fluid Milk Utilizing a Selective Preliminary Incubation

1989 ◽  
Vol 52 (11) ◽  
pp. 805-807 ◽  
Author(s):  
R. D. BYRNE ◽  
J. R. BISHOP ◽  
J. W. BOLING
Keyword(s):  
Shelf Life ◽  
Benzalkonium Chloride ◽  
Fresh Sample ◽  
Organoleptic Evaluation ◽  
Detection Techniques ◽  
Psychrotrophic Bacteria ◽  
Whole Milk ◽  
Shelf Life Prediction ◽  
Standard Plate ◽  
Fluid Milk

Selective preliminary incubation, followed by bacterial enumerations or detection techniques, was used to indicate potential shelf-life of pasteurized fluid milk. Commercial whole milk samples, stored at 7°C, were analyzed for bacterial and biochemical parameters and potential shelf-life using daily organoleptic evaluation. Prior to analysis, each sample was subjected to the following preliminary incubations: milk alone, milk with benzalkonium chloride, milk and broth, milk and broth with benzalkonium chloride, and milk and a dairy gram-negative broth. The following bacterial enumerations were conducted: Psychrotrophic Bacteria Count, modified Psychrotrophic Bacteria Count (Petrifilm and agar methods), and Moseley Keeping Quality test (Petrifilm and agar methods). Catalase detection (headspace pressure and flotation time) and impedance detection times were also determined. Initial Standard Plate and Coliform counts (Petrifilm and agar methods) were conducted on each fresh sample but were not used for shelf-life prediction. Many of the preliminary incubations, in conjunction with enumeration or detection combinations, (especially modified Psychrotrophic Bacteria Count and impedance microbiology) gave good correlations to shelf-life (−0.89 and 0.91, respectively). Thus, these methods could be used to indicate the potential shelf-life of pasteurized fluid milk.

Evaluation of the 3M Dry Medium Culture Plate (Petrifilm™ SM) Method for Determining Numbers of Bacteria in Raw Milk1

1984 ◽  
Vol 47 (10) ◽  
pp. 753-755 ◽  
Author(s):  
R. E. GINN ◽  
V. S. PACKARD ◽  
T. L. FOX
Keyword(s):  
Cold Water ◽  
Correlation Coefficients ◽  
Raw Milk ◽  
Water Soluble ◽  
Gelling Agent ◽  
Plate Count ◽  
Suitable Alternative ◽  
Standard Plate Count ◽  
Standard Plate ◽  
Indicator Dye

The 3M Company has developed a sample-ready system (Petrifilm ™ SM) for enumerating bacteria in milk and other food products. The testing unit consists of Standard Methods culture medium coated onto a base film and overlaid with a second film coated with a cold-water-soluble gelling agent and tetrazolium indicator dye. As such, the system is ready to accept samples of product. A pipette or 0.001-ml plate loop continuous pipetting syringe can be used for applying samples. In this study, both methods of sample addition were used and results compared with those of the Standard Plate Count (SPC) and standard Plate Loop (PL) methods for determining bacteria numbers in raw milk. In total, 108 samples were analyzed in duplicate by each of the four methods. The correlation coefficients (r) between the 3M-SPC and SPC, 3M-PL and PL, 3M-PL and SPC and PL and SPC were 0.946, 0.935, 0.941, and 0.974, respectively. Repeatability, as measured by mean log10 variance for duplicate determinations, was essentially the same for the four methods, and in all instances less than 0.005. The mean log10 differences between the SPC and 3M-SPC, and SPC and 3M-PL were, respectively, −0.177 and −0.168. The preceding statistical criteria suggest the Petrifilm™ SM method to be a suitable alternative to the SPC or the PL procedure.

The Limulus Amoebocyte Lysate Assay and the Direct Epifluorescent Filter Technique as Estimators of Potential Shelf-life of Pasteurized Fluid Milk

1990 ◽  
Vol 53 (2) ◽  
pp. 151-153 ◽  
Author(s):  
ROBERT D. BYRNE ◽  
J. RUSSELL BISHOP
Keyword(s):  
Shelf Life ◽  
Benzalkonium Chloride ◽  
Detection Techniques ◽  
Filter Technique ◽  
Psychrotrophic Bacteria ◽  
Limulus Amoebocyte Lysate ◽  
Whole Milk ◽  
Before And After ◽  
Direct Epifluorescent Filter Technique ◽  
Fluid Milk

The Limulus Amoebocyte Lysate Assay, Direct Epifluorescent Filter Technique and modified Psychrotrophic Bacteria Count were used to indicate potential shelf-life of pasteurized fluid milk. Commercial whole milk samples, stored at 7°C, were analyzed for bacterial and biochemical parameters, as well as for potential shelf-life by daily sensory evaluation. Each sample was evaluated before and after the following preliminary incubations: milk alone, milk with benzalkonium chloride, milk and broth, and milk and broth with benzalkonium chloride. The Limulus Amoebocyte Lysate Assay, Direct Epifluorescent Filter Technique, and modified Psychrotrophic Bacteria Count in conjunction with the preliminary incubations, produced relatively high correlations to shelf-life (−0.78, −0.85, and −0.86 respectively). Thus, these bacterial detection techniques could be used as rapid methods of shelf-life estimation.

Evaluation of Dry Sheet Medium Culture Plate (Compactdry TC) Method for Determining Numbers of Bacteria in Food Samples

2000 ◽  
Vol 63 (5) ◽  
pp. 665-667 ◽  
Author(s):  
SHINGO MIZUOCHI ◽  
HIDEMASA KODAKA
Keyword(s):  
Cold Water ◽  
Correlation Coefficients ◽  
Food Samples ◽  
Water Soluble ◽  
Gelling Agent ◽  
Plate Count ◽  
Aerobic Bacteria ◽  
Suitable Alternative ◽  
Standard Plate Count ◽  
Standard Plate

The Compactdry, a ready-to-use and self-diffusible dry medium sheet culture system, has been developed by the Nissui Pharmaceutical Co. Ltd. for enumerating bacteria in food. The Compactdry consists of special spread sheet with culture medium that is the same as standard method nutrients, a cold water-soluble gelling agent, and a unique plastic dish. The procedure for bacterial examination in a sample solution (1 ml) is to just inoculate a test solution into the center of the self-diffusible medium and incubate at 35°C for 48 h. The Compactdry TC (CTC) for the enumeration of total aerobic bacteria from 97 food samples was compared with the standard plate count (SPC) method and 3M Petrifilm aerobic count plates (PAC). The correlation coefficients between the CTC and SPC method, the CTC and PAC, and the PAC and SPC method were 0.97, 0.99, and 0.97, respectively. The Compactdry system is useful for the enumeration of total aerobic bacteria in food and may be a possible suitable alternative to the conventional pour-plate or the Petrifilm plate methods.

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.

Subpasteurization Heat Treatment to Inactivate Lipase and Control Bacterial Growth in Raw Milk

1982 ◽  
Vol 45 (6) ◽  
pp. 513-515 ◽  
Author(s):  
G. F. SENYK ◽  
R. R. ZALL ◽  
W. F. SHIPE
Keyword(s):  
Heat Treatment ◽  
Lipase Activity ◽  
Raw Milk ◽  
Heat Treatments ◽  
Plate Count ◽  
Psychrotrophic Bacteria ◽  
Standard Plate Count ◽  
Heat Treated ◽  
Standard Plate ◽  
And Control

Raw milk was heat-treated under subpasteurization and suprapasteurization conditions, cooled and stored for up to 72 h at 4.4 and 6.7°C. Milk lipase activity and bacteria counts were monitored in both unheated and heated milks. Inhibition of milk lipase activity ranged from 42 to 98% for treatments of 57.2°C for 10 sec to 73.9°C for 10 sec, respectively. The logs of Standard Plate Count after 72 h of storage at 6.7°C were 6.56, 4.86, 4.31, 4.00 and 2.82 for unheated and 10-sec heat treatments at 57.2, 65.6, 73.9 and 82.2°C, respectively. Psychrotrophic Bacteria Counts were also lower in the heated milks than in the unheated milk. The logs of Psychrotrophic Bacteria Counts after 72 h of storage at 6.7°C were 6.21, 2.45, 2.27, 1.33 and 1.00 for unheated and 10-sec heat treatments at 57.2, 65.6, 73.9 and 82.2°C, respectively. Heat treatment of raw milk supplies would result in limiting action of the milk lipase system and growth of bacteria.

Collaborative Study of the Impedance Method for Examining Raw Milk Samples

1984 ◽  
Vol 47 (9) ◽  
pp. 707-712 ◽  
Author(s):  
R. FIRSTENBERG-EDEN
Keyword(s):  
Collaborative Study ◽  
Raw Milk ◽  
Plate Count ◽  
Impedance Method ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Automated Method ◽  
Significant Difference ◽  
Standard Plate ◽  
Contamination Levels

The impedance method is a rapid automated method for determining bacteriological contamination levels. A collaborative study was done to establish the reproducibility of the impedance method in predicting counts of raw milk. Frozen and unfrozen raw milk samples, with counts in the range of 9 × 104 to 4 × 107 CFU/ml, were sent to six laboratories to be examined by the standard plate count method (SPC) and by the impedance method which produced Bactometer-predicted counts (BPC). The impedance results showed less variability than SPC among laboratories in all three trials. The variance between split samples was also smaller for the impedance method than for SPC. However, the variance between duplicate plates of the same sample was significantly smaller for SPC than for BPC. In one trial, the means of BPC and SPC were not significantly different, whereas in another trial there was a significant difference of ca. log10 0.27 between the means of the two methods. However, in this trial the extreme differences between laboratories counting the same sample were log10 0.42.

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