High-Pressure Processing Revolutionizes Food And Pharmaceutical Industries

By Dr. Chinta SidharthanReviewed by Lily Ramsey, LLMJul 1 2024

The pharmaceutical and food industries routinely use high-pressure processing to create emulsions, homogenize gels and suspensions, extend product shelf life, inactivate microbial growth, and open and extract meat from molluscs and crustaceans.

However, high pressure is known to impact the structure of biomolecules such as proteins. In a recent study published in Food Chemistry Advances, researchers discussed how high pressure impacts protein structure, unfolding, refolding, and crystallization.

​​​​​​​Study: Effect of high-pressure on protein structure, refolding, and crystallization. Image Credit: Eaum M/Shutterstock.com

High-Pressure Processing

The approval of high-pressure processing as a reliable option for non-thermal pasteurization has led to widespread acceptance and application of this technology in the food and pharmaceutical industries.

The property of high pressure to inactivate microbial growth and prevent spoilage is used extensively to increase the shelf life of consumables products.

Seafood, meats, fruits, and dairy are the most common products processed using high pressure. However, pharmaceutical products such as medicines can be sterilized using high-pressure processing devices such as hydraulic-driven boosters, air-driven air pressure amplifiers, homogenizers, oxygen gas boosters, etc.

Although the process has numerous advantages, such as homogeneity, minimal flavor change, and efficient inactivation of bacteria, viruses, and molds, among others, one of the major drawbacks is the need for expensive equipment and pressure-safe materials.

High pressure can also alter the molecular structure of various biomolecules and compounds, which can be advantageous or disadvantageous.

In the present study, the researchers discussed the impact of high-pressure processing on the structure, unfolding, refolding, and crystallization of proteins to determine whether this sterilization and preservation process should continue for protein-rich foods.

Impact on Protein Structure

Proteins are composed of amino acids joined together through polypeptide bonds, which undergo various types of folding to form secondary, tertiary, and quaternary structures. Even minute changes, such as one amino acid, can alter the protein structure and function.

The exposure of protein to high pressure can result in reversible or non-reversible alterations in the inter- and intra-molecular interactions. Pressure below 200 megapascals (MPa) often has a reversible effect, such as polymeric structures getting dissociated into various subunits. Pressures above 200 MPa, however, can denature the protein and cause enzyme inactivation.

High pressure breaks down the non-covalent and hydrogen bonds and the hydrophobic and electronic interactions that hold together proteins' secondary, tertiary, and quaternary structures.

These changes also impact the stability of the protein. However, disulfide bonds also play an important role in the folding and stabilization of proteins, and high pressure has been found to form new sulfide bonds in some cases.

The researchers discussed how the variables in high-pressure processing, such as holding time and pressure levels, impact the extent of denaturation and protein stability. Eventually, the change in protein structure is dependent on variables in the high-pressure processing variables and product variables.

The study also presented how product variables impacted proteins such as β-lactoglobulin, ovalbumin, lysozyme, peroxidase and polyphenol oxidase enzymes, myofibrillar protein, and milk enzymes.

Additionally, the researchers discussed methods to optimize the high-pressure processing methods to minimize protein structure damage.

Impact on Protein Refolding

Protein misfolding has been linked to serious human diseases such as Alzheimer's disease and cystic fibrosis. The folding of the protein determines not only its stability but also its function.

Cell-based expression is a method that allows biologically active compounds to be produced affordably at a large scale, and most of the recombinant proteins produced are non-native, inactive biopolymers.

These proteins need to be refolded to form biologically active forms of proteins, and high-pressure processing can impact the folding and refolding of these proteins to differing degrees.

For example, in the case of bovine serum albumin, high pressure causes protein aggregation, while high pressure causes the unfolding and denaturation of myofibrillar protein.

The study discussed the various parameters, such as dilution rate, redox conditions, and pH, that impact the refolding of proteins. The researchers also examined how high hydrostatic pressure could be applied to fold, unfold, and refold proteins.

Impact on Protein Crystallization

Proteins are enantiomeric; they exist in two forms: non-superimposable and mirror images of each other.

Therefore, they cannot form prismatic or polyhedral crystals and can be damaged easily due to radiation or temperature. However, proteins are less prone to denaturation and more stable in a crystalline lattice form.

The researchers presented a comprehensive summary of how proteins crystallize and the factors that might stimulate or improve the protein crystallisation process. They also discussed the impact of high pressure on protein crystallization, which often depends on the protein type. Proteins such as lysozyme become more soluble under high pressure and do not form crystals, while glucose isomerase forms tetragonal crystals under increasing pressure.

Conclusions

The study presented a detailed overview of high-pressure processing and its applications in the pharmaceutical and food industry.

The researchers also examined how high pressure impacts the structure, refolding, and crystallization of different types of proteins.

The findings indicated that given that different proteins show highly variable stability, refolding, and crystallizing behavior under high pressure, it is difficult to make generalizable conclusions about the impact of high pressure on proteins.

Therefore, high-pressure processing must be applied based on the proteins constituting the product and after examining the stability of the protein under the processing conditions.