How Can Ultrasound be Used to Regulate Foods?

By Samudrapom DamReviewed by Susha Cheriyedath, M.Sc.Sep 6 2022

A paper recently published in the journal Trends in Food Science & Technology reviewed the use of ultrasound food processing technology to regulate the food ingredient interactions in protein-based food matrices.

Study: Ultrasound: A reliable method for regulating food component interactions in protein-based food matrices. Image Credit: HOMONSTOCK/Shutterstock.com

Background

Protein-based food matrices are primarily complex systems composed of polyphenols, lipids, polysaccharides, and proteins that supply essential nutrients and energy to the human body.

Proteins are typically found in different shapes and molecular conformations. The interactions of proteins with the other matrix components, such as water and polyphenol, vary depending on the structural conformations of the protein.

These interactions critically influence the properties of the food matrices, specifically the qualitative characteristics, such as digestibility, mouthfeel, and texture, which has increased the importance of regulating the food component interactions.

Traditional methods used to regulate these interactions are often accompanied by heat formation, leading to excessive molecular aggregation and overall degradation of product quality.

Emerging technologies, such as pulsed electric fields, microwave, ultrasound, and high-hydrostatic pressure are considered suitable for modifying different protein-based food characteristics by regulating the food component interactions.

Among them, ultrasound has gained considerable attention as it is an eco-friendly and effective food processing technology that can favorably impact the functionality of various food components.

Although ultrasound is used in the food industry to prepare novel protein-based products with superior properties, more improvements are required before commercialization.

In the last few years, studies have primarily focused on enhancing the physicochemical properties of protein-based food matrices using ultrasonic treatment.

The Study

In this study, researchers reviewed the effects of ultrasound on the non-covalent and covalent interactions between protein and other dietary components present in protein-based food matrices. Researchers also discussed the techniques used to analyze these interactions.

Interaction Patterns after Ultrasound

Non-covalent Interactions

Non-covalent bonding is the most common food-ingredient interaction in protein-based food matrices. Hydrogen bonding, hydrophobic interactions, and electrostatic interactions are the major non-covalent interactions in food matrices.

Ultrasound can effectively improve the strength of electrostatic interactions by increasing the electrostatic contact between protein and other dietary components. For instance, the electrostatic interactions between citrus pectin and soy protein isolate from defatted soybean meal were enhanced using 22 kHz ultrasound treatment at 25 ^oC and 360-720 W for 5-20 min.

Hydrophobic interactions are the driving force behind protein folding. Hydrophobic forces between different dietary ingredients are enhanced when the original protein structure is disrupted by the robust cavitation of ultrasound.

For instance, hydrophobic interactions between lutein and red bean protein from red bean flour were improved when 20 kHz ultrasound was used at 20-30 ^oC and 60−102 W/cm² for 10-20 min.

Hydrogen bonding is crucial for binding proteins to other components in protein-based food matrices. Ultrasonic treatment can increase the hydrogen bonding between dietary components by increasing the available hydrogen bond receptors and donors.

The hydrophobic interactions and hydrogen bonds between baicalein and Myofibrillar protein (MPN) from chicken breast were improved using 20/23 kHz at 4 ^oC and 60−102 W/cm² for 0-8 min.

However, excessive ultrasound treatment can lead to undesired refolding of the protein structure, reducing the strength of non-covalent forces. Thus, selecting the optimal power density and/or frequency is necessary to progressively improve the sensory and physicochemical qualities of food.

Covalent Interactions

Covalent interactions between proteins and other dietary components in protein-based food matrices are considerably stronger compared to non-covalent interactions. Moreover, covalent complexes also demonstrate higher stability and antioxidant capacity than non-covalent samples.

Ultrasound can facilitate and promote covalent interactions by modifying proteins through their specific sonochemical and sonophysical qualities. However, the matrix composition plays a critical role in modulating the influence of ultrasonic treatment on food ingredient interactions.

For instance, the change in covalent bonding between protein and polyphenol was higher after ultrasound treatment compared to covalent bonding between protein and polysaccharide. Maillard reaction (MAR) and phenolic modification are the most common ultrasonication examples in the food matrix.

Factors Influencing Food Ingredient Interactions

Typically, extrinsic factors, such as ionic strength, temperature, pH, and ultrasonic processing parameters, and intrinsic factors, such as the protein structure and matrix composition, primarily impact the interactions between proteins and other dietary components during ultrasound treatment. Among these factors, relevant parameters must be selected carefully before the ultrasonic treatment of protein-based food matrices to optimize the ultrasonic effect.

Food Ingredient Interaction Evaluation Methods

Evaluating the food component interactions after an ultrasonic treatment is considerably challenging owing to the complexity of a protein-based food matrix. Phase diagram method, isothermal titration calorimetry (ITC), molecular dynamics simulation (MDS), mass spectra, large amplitude oscillatory shear (LAOS), and microscopy methods are often used to evaluate the food ingredient interactions.

The phase diagram method is used as a supplement technique to assess the variations in food quality caused by food component interactions after ultrasonic treatment, while the ITC is employed to effectively determine the thermodynamic interactions between proteins and other dietary components after the ultrasound. However, ITC has stringent requirements concerning sample quantity, purity, and stability.

MDS, a method based on classical mechanical theory, is often used to understand the non-covalent interaction strength, free energy, energy transfer distance, and solvent-accessible surface area in protein-based food matrices. However, the method is not the most reliable way to investigate food component interactions as the structures of several proteins and other components in the matrix are not clearly defined. 

The use of mass spectroscopy is necessary to investigate covalent bond changes between proteins and other components in the food matrix after ultrasound treatment. X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy are more advantageous than conventional approaches owing to their non-destructive nature.

LAOS provides additional information about nonlinear behavior, which can improve the accuracy of rheological measurements of food ingredient interactions after the ultrasound. However, the LAOS technique is not used extensively in food science as many food scientists do not have experience with rheology, and professionals performing rheological research are not acquainted with the LAOS mechanism.

Microscopy methods, such as transmission electron microscopy, confocal laser electron microscopy, and atomic force microscopy, are typically used to investigate the distinct microstructure of a protein-based food matrix as they can monitor different polymerization stages and morphologies of the matrix.

Effects of Food Ingredient Interactions on the Food Matrix Properties after Ultrasound Treatment

Protein-Water Interactions

Protein-water interactions are improved following ultrasound treatment, leading to an increase in texture and water-holding capacity of the final products. Ultrasound-assisted freezing can accelerate the freezing process by increasing the number of nucleation sites.

Improvements in protein-water interactions between pork protein and water and sodium chloride after ultrasound treatment improved the texture profile, water-holding capacity, and NaCl diffusion of the food matrix.

Protein–Polyphenol Interactions

Ultrasound treatment on the non-covalent interactions between polyphenols and proteins can accelerate polyphenol embedding, leading to changes in the bioavailability and color of final products. Additionally, ultrasonic treatment-induced covalent bond modifications between food components can influence the textural characteristics and antioxidant properties.

For instance, the increase in the strength of protein-phenolics interactions between MPN from Japanese seerfish and water and gallic acid after 20 kHz ultrasonic treatment at 10 ^oC and 400 W for 10 min improved the gel properties of MPN.

Protein-Polysaccharide Interactions

Changes in non-covalent and covalent interactions between polysaccharides and proteins can improve the food matrix characteristics, specifically conformational stability, emulsification, gelling properties, solubility, antioxidant capacity, and flavor.

For instance, the storage stability of fish was increased after the protein-polysaccharide interactions between fish MPN and soybean oil and xanthan gum were enhanced using 20 kHz ultrasound treatment for 12 min at 0 ^oC and 150−600 W.

Protein–Lipid Interactions

Mild ultrasound treatment improves the hydrophobic interactions between lipids and proteins, leading to improvements in storage stability and emulsifying activity. However, excessive sonication treatment can adversely impact the protein-lipid interactions. Thus, selecting the optimal temperature, time, power density, and frequency is necessary to improve the rheological characteristics and stability of emulsions.

Emerging Applications of Protein-based Food Matrices after Ultrasound Treatment

Artificial meat, three-dimensional (3D) printing and multifunctional gels with antioxidant properties and reduced fat and sodium are the major emerging applications of ultrasound-treated protein-based food matrices.

Conclusion

To summarize, the sonochemical and sonophysical properties of ultrasound treatment can effectively enhance the covalent and non-covalent interactions of proteins with other dietary components in protein-based food matrices, which can improve the properties of the matrices. However, more research is required to assess the impact of the sonochemical activity of ultrasound on the covalent interactions of complex protein matrices. 

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