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Safety and Quality Improvement of Milk and Cheese.

Anand, Sanjeev
South Dakota State University
Start date
End date

Objective 1: To study the role of thermoduric bacteria in influencing shelf life of milk products such as cheese.

Objective 2: Reducing the cross contamination in dairy processing environments by controlling bacterial biofilms.

More information

Safety and quality enhancement have always been key words in the management of dairy production and manufacturing systems. The importance has further increased due to ever expanding supply chains and the complexity of operations. The recent signing of Food Safety Modernization Act 2011 (FSMA) puts further emphasis on the safety of the U.S. food supply by shifting the focus of federal regulators from response to prevention of contamination (FDA, 2011). Issues related to the cross contamination of milk at the production level with thermoduric spore formers still remain unresolved. These thermoduric spore-forming bacteria could not only limit the shelf life of milk but can also influence the quality of ripening of cheese. Some of these organisms such as Bacillus cereus are potential pathogens and thus can pose health risks. In addition, the risk posed by the incidence of potential pathogens in raw milk is not clearly understood. Our hypothesis is that it is possible to reduce the cross contamination of milk with bacteria including thermoduric spore formers. This can be accomplished by improving HACCP based management practices, better cleaning strategies especially to prevent bacterial biofilms on contact surfaces, and by combining some non-thermal treatment of milk such as ultrasonication to be able to enhance the effectiveness of pasteurization. It would also be of interest to study the competitive inhibition of thermoduric thermophiles during cheese ripening by the nonstarter lactic acid bacteria.

Study 1: To study the role of thermoduric bacteria in influencing shelf life of milk products such as cheese. Studies will be conducted on incidence, growth and emergence of predominance in thermoduric bacterial counts during the Cheddar cheese making process. Bacterial community specific studies with regard to the spoilage microflora can help us determine and control undesirable biochemical changes occurring in cheese during ripening. During the initial phase of this study, thermoduric and thermophilic sporeformers will be screened at milk reception, holding, and processing steps in a cheese plant. We also plan to take cheese samples with defects and isolate the related spoilage bacteria from these samples. Representative bacterial isolates will be used to manufacture cheese at the lab scale to study the events under controlled conditions. We would also study their interactions with different types of starters that could help control these spoilage bacteria and prevent cheese defects. Studies will also be conducted to evaluate the biochemical activities of these bacteria leading to undesirable changes. Total Nitrogen, Water-soluble Nitrogen, and 12% TCA-soluble Nitrogen will be measured to track the proteolytic changes, while Total free AA levels in pH 4.6-soluble fraction of the cheeses will be determined by the Cd-ninhydrin method. Urea-PAGE of pH 4.6-insoluble fractions of the cheeses during ripening will be conducted to obtain degradation patterns. Free fatty acid analysis will be helpful in monitoring starter esterases, and lipoprotein lipase activities. Study 2: Reducing the cross contamination in dairy processing environments by controlling bacterial biofilms. Our previous studies have revealed the presence of multispecies biofilms on reverse osmosis membranes, many of which were found to be resistant to the current CIP protocols being followed by the industry. Frequent presence of biofilms in dairy processing areas reflects the inadequacy of the currently used CIP protocols. One of the important cleaning steps is the enzyme action that helps to break down the biofilm matrices for better cleaning. We hypothesize that it is possible to identify a cocktail of enzymes that would help clean the biofilms in a more effective manner. We plan to develop in vitro biofilms using resistant bacterial isolates that we have obtained from the membrane biofilm consortia of 2 to 14 months old membrane cartridges from active industrial systems. Such resistant biofilms will be tested against the existing and modified CIP protocols under both static and dynamic conditions in order to identify a better cleaning process. We propose to test enzyme modifications with surfactants and test them against resistant biofilms. Tests will be conducted against the lab grown biofilms that will be developed from the biofilm consortia isolates under both static and dynamic conditions using a biofilm reactor. The cross flow studies will help evaluate the efficacy of the modified process in a simulated environment.

PROGRESS: 2012/10 TO 2013/09
Target Audience: Food and dairy industry. Dairy producers. Researchers. The studies completed under this project generated useful information related to incidence of thermoduric microorganisms during milk production and processing. The results obtained were also shared with the US dairy industry through a national spore symposium organized by the Dairy Research Institute, Chicago. Specific projects taken up in collaboration with dairy plants helped to resolve the microbial quality and spoilage issues due to thermoduric sporeformers during the manufacture of cheese and whey products. Information on the incidence of thermoduric sporeformers and spores in raw milk was shared with the dairy producers around the 1-29 corridor to help improve the microbial quality of raw milk. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? The project has provided several opportunities at both graduate and undergraduate levels of teaching. Two MS students completed their degree programs while working on these projects. Four MS and one Ph.D student is currently working under my advising on research project related to thermodurics and biofilm control. In addition, nine undergraduate research projects were completed under this research program during 2013. How have the results been disseminated to communities of interest? Peer reviewed publications, invited lectures in conferences and national symposia, scientific posters presentations in symposium of American Dairy Science Association, direct interaction with dairy producers, and direct interaction with dairy industry. What do you plan to do during the next reporting period to accomplish the goals? We plan to continue work on the non-thermal applications for inactivating the sporeformers and spores in milk. The studies on the ability of sporeformers to cause corrosion on stainless steel surfaces will also be continued. We have submitted grants in the area of control of biofilms by modifying the milk contact surfaces, and understanding the germination and sporulation mechanisms of thermoduric spores in the dairy environment. If these grants are successful then we will be able to conduct this additional area to achieve the goals as stipulated.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Food Defense and Integrity
Bacterial Pathogens