Bacillus cereus in Refrigerated Milk Submitted to Different Heat Treatments

2009 ◽  
Vol 72 (6) ◽  
pp. 1301-1305 ◽  
Author(s):  
GEORGIANA S. B. AIRES ◽  
EDUARDO H. M. WALTER ◽  
VALÉRIA C. A. JUNQUEIRA ◽  
SALVADOR M. ROIG ◽  
JOSÉ A. F. FARIA
Keyword(s):  
Bacillus Cereus ◽  
Shelf Life ◽  
Storage Period ◽  
Heat Treatments ◽  
Pasteurized Milk ◽  
Standard Plate ◽  
Plate Counts ◽  
Experimental Trials ◽  
Incubation Temperatures

The possibility of the survival, germination, and multiplication of Bacillus cereus in extended-shelf-life milk prompted research into the occurrence of the bacteria in refrigerated milk submitted to different heat treatments. Samples were submitted to ultrapasteurization (138°C for 2 s), “superpasteurization” (96°C for 13 s), and pasteurization (74°C for 15 s) and stored under refrigeration at 4 ± 2°C for up to 6 weeks. The milk was analyzed for its sensory quality and for the quantitative determination of mesophilic and psychrotrophic B. cereus in the vegetative form at incubation temperatures of 7 and 30°C, in addition to standard plate counts and psychrotrophic counts. In the three experimental trials, the psychrotrophic B. cereus counts were below the detection limit of the methodology (<10 CFU/ml) in all of the samples analyzed, independent of the heat treatment and storage period. The count of mesophilic B. cereus was restricted to samples of superpasteurized and pasteurized milk from a single trial, reaching 4.0 × 101 and 7.0 × 105 CFU/ml, respectively. Although the pasteurized milk had higher populations of mesophilic B. cereus after the second week of storage, flavor defects resulting in sensory rejection of the product did not appear before the fourth week of storage. The results of this research indicate that superpasteurization and ultrapasteurization are adequate for maintaining the product at refrigeration temperatures for 6 weeks. Pasteurized milk produced under clean conditions should have a shelf life limited to less than 2 weeks.

Toxin Production by Clostridium botulinum in Pasteurized Milk Treated with Carbon Dioxide

1999 ◽  
Vol 62 (8) ◽  
pp. 872-876 ◽  
Author(s):  
KATHLEEN A. GLASS ◽  
KRISTINE M. KAUFMAN ◽  
ANGELIQUE L. SMITH ◽  
ERIC A. JOHNSON ◽  
JOSEPH H. CHEN ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Shelf Life ◽  
High Density Polyethylene ◽  
Clostridium Botulinum ◽  
Gas Injection ◽  
Toxin Production ◽  
Injection System ◽  
Pasteurized Milk ◽  
Standard Plate ◽  
Plate Counts

The addition of carbon dioxide to milk at levels of <20 mM inhibits the growth of selected spoilage organisms and extends refrigerated shelf life. Our objective was to determine if the addition of CO2 influenced the risk of botulism from milk. Carbon dioxide was added to pasteurized 2% fat milk at approximately 0, 9.1, or 18.2 mM using a commercial gas-injection system. The milk was inoculated with a 10-strain mixture of proteolytic and nonproteolytic Clostridium botulinum spore strains to yield 101 to 102 spores/ml. Milk was stored at 6.1 or 21°C for 60 or 6 days, respectively, in sealed glass jars or high-density polyethylene plastic bottles. Milk stored at 21°C curdled and exhibited a yogurt-like odor at 2 days and was putrid at 4 days. Botulinal toxin was detected in 9.1 mM CO2 milk at 4 days and in all treatments after 6 days of storage at 21°C. All toxic samples were grossly spoiled based on sensory evaluation at the time toxin was detected. Although botulinal toxin appeared earlier in milk treated with 9.1 mM CO2 compared to both the 18.2 mM and untreated milk, gross spoilage would act as a deterrent to consumption of toxic milk. No botulinal toxin was detected in any treatment stored at 6.1°C for 60 days. At 6.1°C, the standard plate counts (SPCs) were generally lower in the CO2-treated samples than in controls, with 18.2 mM CO2 milk having the lowest SPC. These data indicate that the low-level addition of CO2 retards spoilage of pasteurized milk at refrigeration temperatures and does not increase the risk of botulism from treated milk stored at refrigeration or abuse temperatures.

Heterogeneity of Samples as a Problem in Shelf-Life Prediction

1983 ◽  
Vol 46 (6) ◽  
pp. 542-544 ◽  
Author(s):  
R. B. MAXCY ◽  
S. E. WALLEN
Keyword(s):  
Shelf Life ◽  
Common Assumption ◽  
Typical Sample ◽  
Shelf Life Prediction ◽  
Standard Plate ◽  
Plate Counts ◽  
Predicting Behavior ◽  
The Common ◽  
Multiple Samples ◽  
Sample Set

A study of the common assumption that a single package of milk represents the production lot was made. Sensory and microbial observations on shelf-life were of sample sets of sequentially produced cartons of milk from four different commercial operations. Neither spoilage rate nor nature of spoilage was uniform for a typical sample set of ten units. A single package, therefore, provided low probability for predicting behavior of the entire production lot. Observations on individual colonies from standard plate counts at the time of sensory spoilage indicated the microflora to be a pure culture in each spoiled unit. The extreme differences in spoilage rates of individual units within sample sets indicated sensory evaluation of multiple samples to be the most logical, simple criterion for evaluating shelf-life. The size of the sample set to be observed and frequency of sampling awaits further observations and application of statistical techniques to establish the accuracy of estimates desired.

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.

Effect of Delayed Heading on Some Quality Attributes of Penaeus Shrimp1

1979 ◽  
Vol 42 (5) ◽  
pp. 407-409 ◽  
Author(s):  
R. J. ALVAREZ ◽  
J. A. KOBURGER
Keyword(s):  
Panel Data ◽  
Storage Period ◽  
Plate Count ◽  
Sensory Panel ◽  
Bacterial Populations ◽  
Standard Plate Count ◽  
Plate Count Agar ◽  
Pseudomonas Species ◽  
Standard Plate ◽  
Plate Counts

To determine the effect of delayed heading on shrimp quality, shrimp were stored on ice with and without heads for 10 days. Some shrimp were delay-headed after 5 days and returned to ice for the remainder of the storage period. Microbiological studies were conducted at 0, 5 and 10 days of storage. Total aerobic plate counts were done using Standard Plate Count agar with an added 0.5% NaCl. Incubation was at 20 C for 5 days. Analyses indicated similar counts on shrimp tails stored with or without heads and those delayed-headed. Counts ranged from 2.4 × 106 bacteria/gram at 0 day to 1.6 × 109 bacteria/gram on the 10th day. Identification of the flora present revealed that the same major groups of organisms predominated on shrimp tails subjected to the different storage treatments and the head did not alter development of the usual flora. Flavobacterium, Pseudomonas, Planococcus, Moraxella and the Vibrio/Aeromonas group were the major genera encountered. A shift in bacterial populations was observed during storage. Flavobacterium species predominated during the first 5 days of storage; however, after the fifth day Pseudomonas species predominated. Sensory panel data revealed no differences in acceptability between shrimp tails stored with or without heads and those delay-headed.

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.

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 TEMPERATURE AND TIME OF PLATE INCUBATION ON THE ENUMERATION OF PASTEURIZATION-RESISTANT BACTERIA IN MILK1

1963 ◽  
Vol 26 (11) ◽  
pp. 357-363 ◽  
Author(s):  
W. R. Thomas ◽  
G. W. Reinbold ◽  
F. E. Nelson
Keyword(s):  
Incubation Temperature ◽  
Bacterial Count ◽  
Raw Milk ◽  
Effect Of Temperature ◽  
Plate Count ◽  
Resistant Bacteria ◽  
Pasteurized Milk ◽  
Standard Plate Count ◽  
Standard Plate

This study was undertaken to determine the effect of temperature and time of plate incubation upon the count of thermoduric bacteria in milk. Specific types of thermoduric bacteria in pure culture, as well as those present in the mixed flora of commercial milk samples, were enumerated. Plate incubation at 28 C for 4 days was the temperature-time combination that produced the highest thermoduric bacterial count with laboratory-pasteurized milk. Incubation at 21, 32 or 35 C gave lower counts. Thermoduric bacteria subjected to pasteurization were more exacting in their growth temperature requirements than were unheated bacteria. Cultures of Arthrobacter sp., Micrococcus varians and Streptococcus sp. grew over a much wider temperature range before laboratory pasteurization than after the heat treatment. The incubation temperature and time currently recommended for the standard plate count, while presumably adequate for the enumeration of bacteria in raw milk, may not be equally satisfactory for the determination of the maximum viable bacterial population of pasteurized milk.

A Rapid Method for Predicting the Potential Shelf Life of Fresh Broiler Chicken Carcasses

1997 ◽  
Vol 60 (2) ◽  
pp. 148-152 ◽  
Author(s):  
SCOTT M. RUSSELL
Keyword(s):  
Shelf Life ◽  
Pseudomonas Fluorescens ◽  
Linear Correlation ◽  
Broiler Chicken ◽  
Storage Period ◽  
Bacterial Populations ◽  
Standard Methods ◽  
Significant Linear Correlation ◽  
Rapid Enumeration ◽  
Plate Counts

An experiment was conducted to determine if rapid enumeration of populations of Pseudomonas fluorescens by standard methods and by measuring capacitance could be used to predict the potential shelf life of fresh broiler chicken. Fifty whole ready-to-cook broiler chicken carcasses were obtained fresh from the chiller and separated into five groups (10 carcasses each) in three replicate trials. The first 10 carcasses were sampled by rinsing on day 0. Ten carcasses each were sampled by rinsing after holding for 3, 6, 9, or 12 days at 3°C. For each carcass, psychrotrophic plate counts (PPC), P. fluorescens plate counts (PFPC), P. fluorescens detection times (PFDT), and subjective odor evaluations (ODOR) were determined. PPC, PFPC, and ODOR on groups of carcasses significantly increased after 3 days of storage at 3°C and every day thereafter throughout the storage period. The log Pseudomonas fluorescens detection times (LPDT) significantly decreased throughout storage from 0 to 12 days, indicating a significant increase in bacterial populations. Significant linear and quadratic correlations, respectively, were observed between PPC and day of storage (DAY) (R2 = .86 and .84), PFPC and DAY (R2 = .85 and .89), LPDT and DAY (R2 = .86 and .85), ODOR and DAY (R2 = .73 and .86), PPC and ODOR (R2 = .80 and .72), PFPC and ODOR (R2 = .87 and .81), LPDT and ODOR (R2 = .85 and .77), and LPDT and PPC (R2 = .96 and .97). A significant linear correlation was observed between LPDT and PFPC (R2 = .93). Enumeration of P. fluorescens from fresh chicken at day of processing should be beneficial because (i) the potential shelf life of fresh chicken can be determined at day of processing; (ii) processing sanitation hygiene may be determined; and (iii) carcasses exposed to temperature abuse may be identified.

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.

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