In vitro interactions between probiotic bacteria and milk proteins probed by atomic force microscopy

Area of Science:

• Food Microbiology
• Biochemistry
• Materials Science

Background:

• Microbial cell location in dairy matrices is influenced by interactions with milk proteins.
• Understanding these interactions is crucial for probiotic delivery and product texture.

Purpose of the Study:

• To investigate the interactions between two Lactobacillus rhamnosus strains (GG and GR-1) and different milk proteins (micellar casein, native and denatured whey proteins).
• To characterize bacterial surface properties and their influence on protein binding.
• To determine the specificity of these interactions based on bacterial strain, protein type, and environmental pH.

Main Methods:

• Bacterial surface characterization using X-ray photoelectron spectroscopy (XPS) to analyze surface composition (proteins, polysaccharides, lipids).
• Electrophoretic mobility measurements to determine surface charge of bacteria and proteins across a pH range (3-7).
• Atomic force microscopy (AFM) to visualize and identify the nature of bacterial-protein interactions.

Main Results:

• Atomic force microscopy revealed specific interactions between Lactobacillus rhamnosus strains and whey proteins, contrasting with non-specific interactions with micellar casein.
• The GG strain exhibited more significant specific interactions with whey proteins compared to the GR-1 strain, indicating strain-specific matrix adherence.
• Bacterial surface composition and charge, protein type, and media pH were identified as key factors influencing microbial-dairy matrix interactions.

Conclusions:

• Microbial-dairy matrix interactions are strain-specific, influenced by bacterial surface properties and protein characteristics.
• Specific binding events, particularly with whey proteins, play a significant role in probiotic cell adhesion.
• The findings provide insights into optimizing probiotic survival and distribution in dairy products.