Microbiological Safety of Cheese Made from Heat-Treated Milk, Part III. Technology, Discussion, Recommendations, Bibliography

1990 ◽  
Vol 53 (7) ◽  
pp. 610-623 ◽  
Author(s):  
ERIC A JOHNSON ◽  
JOHN H. NELSON ◽  
MARK JOHNSON
Keyword(s):  
Heat Treatment ◽  
Whey Protein ◽  
Raw Milk ◽  
Toxin Production ◽  
Ph Control ◽  
Heat Treatments ◽  
Low Risk ◽  
Pasteurized Milk ◽  
Psychrotrophic Bacteria ◽  
Heat Treated

Heat treatment or pasteurization does not adversely affect the cheesemaking process or the resulting physical properties of the cheese. Both types of heat-treatments can correct chemical changes that occur in cold stored raw milk. Thermization on the farm may help control psychrotrophic bacteria in cold stored milk. Some denaturation of whey protein does occur during pasteurization. Heat treatments slightly above current minimum pasteurization requirements can cause body/texture and moisture control problems in cheese. Loss of functionality can adversely affect the marketing of whey protein products. Cheeses made from pasteurized milk ripen more slowly and usually do not exhibit the flavor intensity of cheeses made from raw or heat-treated milk. Swiss and hard Italian type cheese, whose traditional flavor results in part from native milk enzymes and microflora, would also be adversely affected if milk pasteurization for cheesemaking were mandatory. The quality of cheese made from pasteurized milk is consistently better than cheese made from raw milk as evidenced by fewer body and flavor defects consequent to the growth of undesirable bacteria. Either pasteurization or heat-treatment enables improved uniform process control and quality during cheesemaking. Pathogens were prioritized as high, medium, or low risk in cheese. Three organisms, Salmonella, Listeria monocytogenes and enteropathogenic Escherichia coli were judged to be high risk threats to the cheese industry. Staphylococcus aureus was listed as low risk because growth and toxin production is readily suppressed by lactic cultures and acidity (pH) control in cheese. Three actions are recommended:Establish a guideline for minimum heat-treatment of milk for cheesemaking: 64.4°C (148°F) for 16 s or equivalent with adequate process control.Evaluate current safety technology and practices used for cheese manufacture. Support research with primary emphasis on the combined effect of heat-treatment and other current cheese technologies.Evaluate technologies not currently utilized in cheese manufacture for safety potential.

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.

Microbiological Safety of Cheese Made from Heat-Treated Milk, Part II. Microbiology

1990 ◽  
Vol 53 (6) ◽  
pp. 519-540 ◽  
Author(s):  
ERIC A. JOHNSON ◽  
JOHN H. NELSON ◽  
MARK JOHNSON
Keyword(s):  
Escherichia Coli ◽  
Heat Treatment ◽  
Raw Milk ◽  
Causative Factor ◽  
Ph Control ◽  
The United States ◽  
Curing Conditions ◽  
Microbiological Safety ◽  
Heat Treated ◽  
The U.S

A review of epidemiological literature identified six illness outbreaks transmitted via U.S. produced cheese during 40 years, 1948–1988. During these four decades, the United States cheese industry produced over 100 billion pounds of natural cheese (not including cottage and related varieties). The most frequent causative factor in U.S. and Canadian cheese-related outbreaks was post-pasteurization contamination. Faulty pasteurization equipment or procedures were implicated in one outbreak each in the U.S. and Canada. Use of raw milk was a factor in one outbreak in each country. Inadequate time-temperature combinations used for milk heat treatment were not implicated. The epidemiology of cheese-related outbreaks in the U.S., Canada, and Europe demonstrated that soft surface-ripened cheese, e.g. Camembert and Brie, are at significantly greater risk to transmit pathogens than other cheeses. No outbreaks were linked to hard Italian varieties, e.g. Parmesan, Romano, and Provolone. Varieties such as Cheddar and Swiss were infrequently involved. A variety of pathogens have been isolated from raw milk. Some, including Salmonella, Listeria, and enteropathogenic Escherichia coli can survive and grow in some cheeses. In one of the few published studies of milk heat-treatment for cheesemaking, multistrain or species mixtures of pathogens were inoculated into raw milk at levels of 105/ml which was heat-treated in a commercial HTST pasteurizer — mean holding time 17.6 s, minimum 16.2 s. All strains of Yersinia enterocolitica, Campylobactersp., Escherichia coli 0157:H7, and all but one Salmonella species were destroyed at 65°C (149°F). Salmonella senftenberg (rarely isolated from cheese) was inactivated at 69°C (156.2°F). Listeria monocytogenes in naturally contaminated milk at levels of 104 organisms per ml was inactivated at 66°C (150.8°F); laboratory-cultured inoculum at levels of 105 organisms per ml required 69.0°C (156.2°F). A multiplicity of practices other than pasteurization or heat-treatment contribute significantly to the microbiological safety of cheese. Some, such as milk quality management, lactic culture management, pH control, salt addition, and controlled curing conditions are established technologies. Others represent potential opportunities, such as natural inhibitory substances in milk, antibacterial substances, e.g. nisin and lysozyme.

scholarly journals The influence of applied heat treatments on whey protein denaturation

2002 ◽  
Vol 47 (2) ◽  
pp. 205-218
Author(s):  
Safet Fetahagic ◽  
Ognjen Macej ◽  
Jelena Denin-Djurdjevic ◽  
Snezana Jovanovic
Keyword(s):  
Heat Treatment ◽  
Whey Protein ◽  
Protein Denaturation ◽  
Skim Milk ◽  
Heat Treatments ◽  
Matter Content ◽  
90 C 10 ◽  
Milk Samples ◽  
Heat Treated ◽  
Sera Samples

Reconstituted skim milk with 8.01% DM was standardized with 3% skim milk powder and with 3% demineralized whey powder (DWP), respectively. Gained milk samples are named as 8%, 11% and 8%+3%DWP. All samples were heat treated at 85?C/10 min, 90?C/10 min and 95?C/10 min, respectively. Untreated milk was used as control. Milk samples were coagulated by glucono-d-lactone (GDL) at the temperature of 45?C until pH 4.60 was reached. Milk nitrogen matter content decreased during heat treatments, but linear relationship between applied heat treatments and nitrogen matter decreasing was not found. Nitrogen matter content of sera gained from both untreated and heat treated milk increased with the increase of milk dry matter content and with the addition of DWP. The higher temperature of applied heat treatment, the smaller sera nitrogen matter content. Nitrogen matter content in sera obtained from untreated milk were 64.90 mg%, 96.80 mg% and 117.3 mg% for milk 8%, 11% and 8%+3.0% DWP, respectively. Sera samples obtained from milk 8% heat treated at 85?C/10 min, 90?C/10 min and 95?C/10 min had 38.70 mg% 38.30 mg% and 37.20 mg% of nitrogen matter, respectively. Sera samples obtained from milk 11% heat treated at 85?C/10 min, 90?C/10 min and 95?C/10 min had 55.90 mg%, 52.80 mg% and 51.30 mg% of nitrogen matter, respectively. Sera samples obtained from milk 8% heat treated at 85?C/10 min, 90?C/10 min and 95?C/10 min had 69.50 mg%, 66.20 mg% and 66.00 mg% of nitrogen matter respectively. Distribution of nitrogen matter from untreated milk to milk sera were 12.01%, 11.14% and 17.69% for milk 8%, 11% and 8%+3.0% DWP respectively. Distribution of nitrogen matter from milk 8% heat treated at 85?C/10 min, 90?C/10 min and 95?C/10 min to sera samples were 6.99%, 6.72% and 6.59%, respectively. Distribution of nitrogen matter from milk 11% heat treated at 85?C/10 min, 90?C/10 min and 95?C/10 min to sera samples, were 6.02%, 5.32% and 5.21%, respectively. Distribution of nitrogen matter from milk 8%+3%DWP heat treated at 85?C/10 min, 90?C/10 min and 95?C/10 min to sera samples were 9.64%, 8.66% and 8.67%, respectively. Whey protein denaturation increased with increasing of the temperature of the applied heat treatment. Denaturation was the most significant for milk sample 11%.

Inhibition of the Psychrotrophic Bacteria of Raw Milk by Addition of Lactic Acid Bacteria

1990 ◽  
Vol 53 (5) ◽  
pp. 400-403 ◽  
Author(s):  
C. P. CHAMPAGNE ◽  
F. GIRARD ◽  
N. MORIN
Keyword(s):  
Heat Treatment ◽  
Lactic Acid ◽  
Lactic Acid Bacteria ◽  
Pseudomonas Putida ◽  
Inhibitory Activity ◽  
Raw Milk ◽  
Pasteurized Milk ◽  
Psychrotrophic Bacteria

Two commercial cultures of lactic acid bacteria (LAB) were added to raw milk in order to inhibit the development of psychrotrophic bacteria. The effects of inoculation level, pH development, media for culture preparation, and milk heat treatment on the inhibitory activity of LAB were studied. Inoculation levels of 2.5 × 106/mL and less of LAB did not significantly reduce psychrotrophic growth. Maximum inoculation level of LAB studied was 25 × 106/mL and this reduced psychrotrophic development by a factor of 10; however, milk pH was reduced to 6.54 over 48 h of incubation at 7°C with this inoculation level. This acidification was not responsible for the inhibitory activity of LAB on psychrotrophs. The LAB were more effective when psychrotroph populations had high multiplication rates. Initial populations of Pseudomonas putida in pasteurized milk did not influence the activity of the LAB. Pseudomonas putida grew faster in sterile milk than in pasteurized milk, but average inhibition rates of LAB were similar in both media.

Bacteriological Survey of Freshly Formed Cheddar Cheese

1984 ◽  
Vol 47 (7) ◽  
pp. 546-548 ◽  
Author(s):  
MICHAEL H. BRODSKY
Keyword(s):  
Heat Treatment ◽  
Staphylococcus Aureus ◽  
Geometric Mean ◽  
Cheddar Cheese ◽  
Raw Milk ◽  
Fecal Coliforms ◽  
Salmonella Spp ◽  
Pasteurized Milk ◽  
Heat Treated ◽  
Raw Milk Cheese

Two hundred-fifty freshly formed cheese samples produced by 32 provincially inspected cheese plants were analyzed by 7 regional laboratories of the Ontario Ministry of Health. Coliforms were detected in 61 (25.8%) and fecal coliforms confirmed in 46 (19.5%) of the 236 samples tested, with geometric mean counts per g of 133 and 136, respectively. The incidence of coliforms was highest in Cheddar cheeses made from pasteurized milk (29.7%) compared with the incidence of raw milk cheese (22.0%) and cheese made from milk which had been subjected to sub-pasteurization heat treatment (28.2%). Conversely, the incidence of fecal coliforms was lowest in pasteurized milk cheese (17.8%), followed by raw milk cheese (22.0%) and highest in heat-treated milk cheeses (25.6%). Staphylococcus aureus above the screening level of 1000 per g was not found in any of the 237 samples analyzed. Salmonella spp. were not detected in any of the 250 samples. These results suggest that producers of Cheddar cheese should have no difficulty in meeting the microbiological standards adopted by the Health Protection Branch, Health and Welfare Canada.

A survey of the incidence of coagulase-positive staphylococci in market milk and cheese in England and Wales

1965 ◽  
Vol 32 (2) ◽  
pp. 187-192 ◽  
Author(s):  
M. Elisabeth Sharpe ◽  
B. Gillian Fewins ◽  
B. Reiter ◽  
W. A. Cuthbert
Keyword(s):  
Heat Treatment ◽  
Raw Milk ◽  
Heat Treatments ◽  
England And Wales ◽  
Heat Treated ◽  
Cheese Curd ◽  
Coagulase Positive Staphylococci

SummaryThe occurrence of coagulase-positive staphylococci in 954 samples of raw or heat-treated market milk and in 910 samples of cheese of different varieties, taken at 40 cheese factories or farms in England and Wales was determined. Only 9% of the cheeses contained more than 500 000 staphylococci/g, and these were all made from raw milk. All but the mildest of the heat treatments used were effective in greatly reducing the numbers of staphylococci present in milk and usually resulted in cheese virtually free from staphylococci. The effect of sublethal heat treatment on multiplication of these organisms in cheese curd is discussed.

scholarly journals Changes in Native Whey Protein Content, Gel Formation, and Endogenous Enzyme Activities Induced by Flow-Through Heat Treatments of Goat and Sheep Milk

Dairy ◽  
2021 ◽  
Vol 2 (3) ◽  
pp. 410-421
Author(s):  
Golfo Moatsou ◽  
Ekaterini Moschopoulou ◽  
Evangelia Zoidou ◽  
Aggeliki Kamvysi ◽  
Dimitra Liaskou ◽  
...  
Keyword(s):  
Whey Protein ◽  
Enzyme Activities ◽  
Goat Milk ◽  
Raw Milk ◽  
Heat Treatments ◽  
Clotting Time ◽  
Sheep Milk ◽  
Native Whey ◽  
Flow Through ◽  
Water Holding

The aim of the present study was to assess the effects of different flow-through heat treatments—68, 73, 78, 85, 100 °C for 16 s—applied to in-line homogenized goat and sheep milk. Alkaline phosphatase (ALP) activity in raw goat milk was 324.5 ± 47.3 μg phenol/mL, and that of lactoperoxidase (LPO) was 199.3 ± 6.7 U/L. The respective activities in raw sheep milk were 7615 ± 141 μg phenol/mL and 319 ± 38.6 U/L. LPO activity was not detected in both milk kinds treated at 85 °C for 16 s. Residual enzyme activities at 73 °C for 16 s with respect to the initial levels in raw milk were higher in goat than in sheep milk. The whey protein fraction of sheep milk was more heat sensitive compared to goat counterpart. Sheep milk rennet clotting time (RCT) was not affected by the treatments, while curd firmness decreased significantly (p < 0.05) at 100 °C for 16 s. Treatments more intense than 73 °C for 16 s increased the RCT of goat milk significantly but inconsistently and decreased curd firmness significantly, while yoghurt-type gels made from 73 °C or 78 °C for 16 s treated goat milk exhibited the highest water-holding capacity.

scholarly journals Electron Beam Melting of Ti-6Al-4V Lattice Structures; Correlation between Post Heat Treatment and Mechanical Properties

2021 ◽  
Author(s):  
Giuseppe Del Guercio ◽  
Manuela Galati ◽  
Abdollah Saboori
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Computer Aided Design ◽  
Mechanical Performance ◽  
Industrial Applications ◽  
Heat Treatments ◽  
Layer By Layer ◽  
Lattice Structures ◽  
Heat Treated ◽  
Aided Design

Abstract Additive Manufacturing processes are considered advanced manufacturing methods. It would be possible to produce complex shape components from a Computer-Aided Design model in a layer-by-layer manner. Lattice structures as one of the complex geometries could attract lots of attention for both medical and industrial applications. In these structures, besides cell size and cell type, the microstructure of lattice structures can play a key role in these structures' mechanical performance. On the other hand, heat treatment has a significant influence on the mechanical properties of the material. Therefore, in this work, the effect of the heat treatments on the microstructure and mechanical behaviour of Ti-6Al-4V lattice structures manufactured by EBM was analyzed. The main mechanical properties were compared with the Ashby and Gibson model. It is very interesting to notice that a more homogeneous failure mode was found for the heat-treated samples. The structures' relative density was the main factor influencing their mechanical performance of the heat-treated samples. It is also found that the heat treatments were able to preserve the stiffness and the compressive strength of the lattice structures. Besides, an increment of both the elongation at failure and the absorbed energy was obtained after the heat treatments. Microstructure analysis of the heat-treated samples confirms the increment of ductility of the heat-treated samples with respect to the as-built one.

Mechanical Behaviour of Gas Nitrided Ti6Al4V Bars Produced by Selective Laser Melting

2016 ◽  
Vol 704 ◽  
pp. 225-234 ◽  
Author(s):  
Peter Franz ◽  
Aamir Mukhtar ◽  
Warwick Downing ◽  
Graeme Smith ◽  
Ben Jackson
Keyword(s):  
Heat Treatment ◽  
Selective Laser Melting ◽  
Nitrided Layer ◽  
Xrd Analysis ◽  
Compound Layer ◽  
Processing Parameters ◽  
Heat Treatments ◽  
Laser Melting ◽  
Gas Nitriding ◽  
Heat Treated

Gas atomized Ti-6Al-4V (Ti64) alloy powder was used to prepare distinct designed geometries with different properties by selective laser melting (SLM). Several heat treatments were investigated to find suitable processing parameters to strengthen (specially to harden) these parts for different applications. The results showed significant differences between tabulated results for heat treated billet Ti64 and SLM produced Ti64 parts, while certain mechanical properties of SLM Ti64 parts could be improved by different heat treatments using different processing parameters. Most heat treatments performed followed the trends of a reduction in tensile strength while improving ductility compared with untreated SLM Ti64 parts.Gas nitriding [GN] (diffusion-based thermo-chemical treatment) has been combined with a selected heat treatment for interstitial hardening. Heat treatment was performed below β-transus temperature using minimum flow of nitrogen gas with a controlled low pressure. The surface of the SLM produced Ti64 parts after gas nitriding showed TiN and Ti2N phases (“compound layer”, XRD analysis) and α (N) – Ti diffusion zones as well as high values of micro-hardness as compared to untreated SLM produced Ti64 parts. The microhardness profiles on cross section of the gas nitrided SLM produced samples gave information about the i) microhardness behaviour of the material, and ii) thickness of the nitrided layer, which was investigated using energy dispersive spectroscopy (EDS) and x-ray elemental analysis. Tensile properties of the gas nitrided Ti64 bars produced by SLM under different conditions were also reported.

GENETICAL STUDIES ON MUTANTS IN THE PROGENY OF HEAT-TREATED BARLEY

1937 ◽  
Vol 15c (5) ◽  
pp. 217-229 ◽  
Author(s):  
F. H. Peto
Keyword(s):  
Heat Treatment ◽  
Mutation Rate ◽  
Heat Treatments ◽  
Plastid Mutation ◽  
Heat Treated ◽  
Natural Mutation

Heat treatments were applied to barley seeds and 10 different mutant characters were observed in the progeny, viz.; xantha1 and 2, dwarf1,2,3 and 4, virescent1 and 2, chlorina and albino. Typical Mendelian ratios were not obtained in the first segregating generation owing to the small size of the sector affected in the generation of treatment. In the second and third segregating generations, good fits were obtained in all cases to either monohybrid or dihybrid ratios. Both 3:1 and 15:1 ratios were observed in lines segregating for xantha1 and albino characters. The postulation of the duplicate factor hypothesis was necessary to explain this situation. Chlorina and dwarf mutants segregated in all the cases investigated as simple Mendelian recessives. One virescent strain was believed to have arisen through plastid mutation and was maternally inherited.The heat treatment significantly increased the natural mutation rate for the xantha characters but apparently had no effect on the albino mutation rate. Dwarf, virescent and chlorina mutants were observed in the segregating generation after heat treatment, but were not detected in untreated populations.

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