Microbial Spoilage Mechanisms in Dairy Products
Summary
Microbial spoilage in dairy products arises from the growth and metabolic activity of indigenous and contaminating microorganisms, notably psychrotrophic bacteria, which thrive at refrigeration temperatures. These organisms secrete extracellular heat-resistant enzymes, including proteases, lipases and phospholipases, that persist through processing steps such as pasteurisation or ultra-high temperature (UHT) treatment. Proteolytic enzymes cleave casein and whey proteins, leading to gelation, sedimentation and off-flavours, while lipolytic activity liberates free fatty acids that impart rancid or bitter notes. Phospholipolysis compromises membrane lipid integrity, promoting emulsion destabilisation and textural defects. In mixed microbial communities, interspecies interactions and biofilm formation on equipment surfaces further enhance enzyme production and resistance to sanitising regimens. Advances in high-throughput sequencing and metabolomic profiling have revealed dynamic shifts in community composition during cold storage and along the cold chain, with opportunistic genera such as Pseudomonas and Acinetobacter frequently dominating. Spoilage mechanisms vary with product type: raw milk quality is undermined by psychrotroph-derived thermostable enzymes, whereas UHT-treated milks exhibit protein aggregation and creaming induced by residual enzyme activity over shelf life. Cheese, yoghurt and other fermented dairy matrices may also suffer textural and sensorial defects through similar pathways. Understanding these mechanisms underpins the development of targeted control strategies, encompassing improved hygienic practices, rapid detection methods and innovative preservation techniques that inhibit enzyme producers without compromising product safety or nutritional value.
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Microbial Spoilage Mechanisms in Dairy Products publication trend
The graph below shows the total number of articles in microbial spoilage mechanisms in dairy products across all publications each year (not limited to Nature Index journals).
Technical terms
Psychrotrophic bacteria: Microorganisms capable of growth and enzyme production at low (refrigeration) temperatures.
Extracellular heat-resistant enzymes: Proteases, lipases or phospholipases secreted by microbes that retain activity after heat treatments.
Proteolysis: Enzymatic cleavage of proteins into peptides or amino acids, leading to destabilisation and off-flavours.
Lipolysis: Enzymatic hydrolysis of triglycerides into free fatty acids, causing rancidity and textural defects.
Phospholipolysis: Hydrolysis of phospholipids, undermining emulsion stability and contributing to creaming and sedimentation.
Biofilm: A structured community of microorganisms adhered to surfaces, encased in a self-produced matrix, enhancing resistance to cleaning.
UHT sterilisation: Ultra-high temperature process that rapidly heats milk to eliminate vegetative microbes while preserving shelf life.
References
- Effect of Thermostable Enzymes Produced by Psychrotrophic Bacteria in Raw Milk on the Quality of Ultra-High Temperature Sterilized Milk. Foods (2023).
- Single Molecule Real-Time Sequencing and Traditional Cultivation Techniques Reveal Complex Community Structures and Regional Variations of Psychrotrophic Bacteria in Raw Milk. Frontiers in Microbiology (2022).
- A Milk Foodomics Investigation into the Effect of Pseudomonas fluorescens Growth under Cold Chain Conditions. Foods (2021).
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