Impact of high hydrostatic pressure treatment on physicochemical characteristics, structural characteristics, and functional characteristics of mare milk casein.

Overview

• This study explores how high hydrostatic pressure (HHP) treatment affects the physicochemical, structural, and functional properties of casein protein derived from mare milk.
• The research reveals that HHP can enhance or modify casein’s solubility, structure, and various functional properties differently depending on the pH level.

Background and Objective

• Casein is the main protein in milk that has important structural and functional roles in food products.
• Mare milk casein is less studied compared to cow milk casein, and understanding how to modify its properties can expand its applications.
• High hydrostatic pressure (HHP) is a non-thermal food processing method known to alter protein structures to improve functionality without using heat.
• The objective of this study was to examine the effects of varying pressures of HHP on mare milk casein’s:
• Physicochemical characteristics (e.g., solubility, turbidity, particle size, surface charge)
• Structural characteristics (e.g., protein conformational changes)
• Functional characteristics (e.g., foaming, emulsifying, water-holding capacity, antioxidant activity, enzyme inhibition)
• Studies were performed at two pH levels (7 and 9) since pH influences protein behavior and function.

Physicochemical Changes Induced by HHP

• Solubility: HHP treatment increased the solubility of mare milk casein, making the protein more dispersible in solution.
• Turbidity: Turbidity, a measure of cloudiness due to suspended particles, was reduced, suggesting enhanced clarity and better dispersion.
• Particle Size: Changes in particle size indicate that HHP influenced protein aggregation or dissociation into smaller or differently sized particles.
• Surface Charge: Alterations in zeta potential (surface charge) affect protein-protein interactions and stability in suspension.

Structural Characteristics and Conformational Changes

• Using structural analysis methods (likely spectroscopy), the study found:
• At pH 7, a decrease in β-sheet content, which represents a specific protein secondary structure, indicating unfolding or rearrangement.
• An increase in hydrophobic exposure, meaning previously buried non-polar regions became accessible due to conformational changes.
• Such structural modifications suggest partial protein unfolding or rearrangements allowing new functional properties to emerge.

Functional Changes at Neutral pH (pH 7)

• Foaming Capacity: Enhanced at 400 MPa HHP, indicating better ability to trap and stabilize air bubbles, useful in dairy foamed products.
• Water-Holding Capacity: Improved under the same pressure, meaning the protein matrix can retain water more effectively, important for texture and juiciness.
• Antioxidant Activity: Decreased, suggesting that some antioxidant components or mechanisms were impaired by HHP at this pH.

Functional Changes at Alkaline pH (pH 9)

• Emulsifying Activity: Improved, indicating better ability to stabilize oil-water mixtures, valuable for dairy emulsions and dressings.
• Antioxidant Activity: Increased, which contrasts with pH 7 results and may be due to pH-dependent structural changes revealing antioxidant sites or forming new active compounds.

Enzyme Inhibition (Xanthine Oxidase)

• High pressure treatment at 600 MPa significantly increased casein’s ability to inhibit xanthine oxidase, an enzyme involved in oxidative processes.
• This suggests added functional benefits relevant to oxidative stress and inflammation management in food or nutraceutical applications.

Implications and Applications

• HHP offers a versatile method to tailor mare milk casein properties for specific food applications by selecting pressure levels and pH conditions.
• Improvements in solubility, emulsification, foaming, and water retention highlight potential in dairy products, beverages, and functional foods.
• Antioxidant activity modulation and enzyme inhibition suggest value-added health benefits could be incorporated.
• This research fills a gap by providing detailed insights into mare milk casein modifications, which could be useful for developing novel mare milk-based products.