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Heat-Resistant Psychrotrophic Bacteria Isolated from Pasteurized Milk 1
C J Washam1, H C Olson1, E R Vedamuthu1
1Department of Dairy Science, Oklahoma State University, Stillwater, Oklahoma 74074.
Journal of Food Protection
|February 9, 2019
Summary
Psychrotrophic bacteria, capable of growth at low temperatures, were found in pasteurized milk with extended shelf life. Many isolates survived pasteurization temperatures and could grow in refrigerated milk, impacting dairy product quality.
Area of Science:
- Food Microbiology
- Dairy Science
- Bacteriology
Background:
- Psychrotrophic bacteria are microorganisms that can grow at low temperatures (refrigeration).
- Their presence in pasteurized milk can lead to spoilage and reduced shelf life, despite processing.
- Understanding these bacteria is crucial for maintaining dairy product quality and safety.
Purpose of the Study:
- To isolate and identify psychrotrophic bacteria from pasteurized milk with extended shelf life.
- To assess the thermal resistance and growth characteristics of these bacteria at refrigeration temperatures.
- To determine the impact of these bacteria on refrigerated milk quality.
Main Methods:
- Isolation of bacteria from 227 pasteurized milk samples.
- Heat resistance testing at 72°C for 16 seconds.
- Growth studies at 7.2°C.
- Identification of bacterial isolates to the genus level.
Main Results:
- 135 out of 700 isolated cultures were heat-resistant and could grow at 7.2°C.
- The most frequent spore-forming genus identified was Bacillus.
- Non-sporing bacteria belonged to the genera Arthrobacter, Microbacterium, Streptococcus, and Corynebacterium.
Conclusions:
- Psychrotrophic bacteria, including Bacillus, Arthrobacter, Microbacterium, Streptococcus, and Corynebacterium, can survive pasteurization and grow in refrigerated milk.
- These resilient bacteria pose a challenge to achieving extended shelf life in dairy products.
- Further research is needed to develop effective control strategies against these psychrotrophic contaminants.
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