Molecular dynamics simulation of high-pressure CO2 pasteurization reveals the interfacial denaturation of proteins at CO2/water interface

Electrostatic interactions of enzymes in non-aqueous conditions: insights from molecular dynamics simulations

Electrostatic interactions of enzymes and their effects on enzyme activity and stability are poorly understood in non-aqueous conditions. Here, we investigate the contribution of the electrostatic interactions on the stability and activity of enzymes in the non-aqueous environment using molecular dynamics simulations. Lipase was selected as active and lysozyme as inactive model enzymes in non-aqueous media. Hexane was used as a common non-aqueous solvent model. In agreement with the previous experiments, simulations show that lysozyme has more structural instabilities than lipase in hexane. The number of hydrogen bonds and salt bridges of both enzymes is dramatically increased in hexane. In contrast to the other opinions, we show that the increase of the electrostatic interactions in non-aqueous media is not so favorable for enzymatic function and stability. In this condition, the newly formed hydrogen bonds and salt bridges can partially denature the local structure of the enzymes. For lysozyme, the changes in electrostatic interactions occur in all domains including the active site cleft, which leads to enzyme inactivation and destabilization. Interestingly, most of the changes in electrostatic interactions of lipase occur far from the active site regions. Therefore, the active site entrance regions remain functional in hexane. The results of this study reveal how the changes in electrostatic interactions can affect enzyme stability and activity in non-aqueous conditions. Moreover, we show for the first time how some enzymes, such as lipase, remain active in a non-aqueous environment.Communicated by Ramaswamy H. Sarma.

The protein-stabilizing effects of TMAO in aqueous and non-aqueous conditions

We present a new water-dependent molecular mechanism for the widely-used protein stabilizing osmolyte, trimethylamine N-oxide (TMAO), whose mode of action has remained controversial. Classical interpretations, such as osmolyte exclusion from the vicinity of protein, cannot adequately explain the behavior of this osmolyte and were challenged by recent data showing the direct interactions of TMAO with proteins, mainly via hydrophobic binding. Solvent effect theories also fail to propose a straightforward mechanism. To explore the role of water and the hydrophobic association, we disabled osmolyte-protein hydrophobic interactions by replacing water with hexane and using lipase enzyme as an anhydrous-stable protein. Biocatalysis experiments showed that under this non-aqueous condition, TMAO does not act as a stabilizer, but strongly deactivates the enzyme. Molecular dynamics (MD) simulations reveal that TMAO accumulates near the enzyme and makes many hydrogen bonds with it, like denaturing osmolytes. Some TMAO molecules even reach the active site and interact strongly with the catalystic traid. In aqueous solvent, the enzyme functions well: the extent of TMAO interactions is reduced and can be divided into both polar and non-polar terms. Structural analysis shows that in water, some TMAO molecules bind to the enzyme surface like a surfactant. We show that these interactions limit water-protein hydrogen bonds and unfavorable water-hydrophobic surface contacts. Moreover, a more hydrophobic environment is formed in the solvation layer, which reduces water dynamics and subsequently, rigidifies the backbone in aqueous solution. We show that osmolyte amphiphilicity and protein surface heterogeneity can address the weaknesses of exclusion and solvent effect theories about the TMAO mechanism.

A Review on the Extraction and Processing of Natural Source-Derived Proteins through Eco-Innovative Approaches

In addition to their nutritional and physiological role, proteins are recognized as the major compounds responsible for the rheological properties of food products and their stability during manufacture and storage. Furthermore, proteins have been shown to be source of bioactive peptides able to exert beneficial effects on human health. In recent years, scholarly interest has focused on the incorporation of high-quality proteins into the diet. This fact, together with the new trends of consumers directed to avoid the intake of animal proteins, has boosted the search for novel and sustainable protein sources and the development of suitable, cost-affordable, and environmentally friendly technologies to extract high concentrations of valuable proteins incorporated into food products and supplements. In this review, current data on emergent and promising methodologies applied for the extraction of proteins from natural sources are summarized. Moreover, the advantages and disadvantages of these novel methods, compared with conventional methods, are detailed. Additionally, this work describes the combination of these technologies with the enzymatic hydrolysis of extracted proteins as a powerful strategy for releasing bioactive peptides.

Quality and Shelf Life of White Shrimp (Litopenaeus vannamei) Processed with High-Pressure Carbon Dioxide (HPCD) at Subcritical and Supercritical States

Phase changes of carbon dioxide (supercritical or subcritical) depend on its proximity to a pressure of 7.35 MPa and temperature of 31.1°C. Carbon dioxide becomes supercritical and subcritical when it is above and slightly below its critical point, respectively. This study aims to determine the effect of high-pressure CO2 treatments at a pressure of 900 psi, 950 psi (subcritical), and 1100 psi (supercritical) and at holding times of 5, 10, and 15 min on the quality parameters of white shrimp (Litopenaeus vannamei) and to determine the shelf life of white shrimp processed with the best treatment. The results showed that the interaction between pressure and holding time had a significant $\left(p<0.05\right)$ effect on cholesterol, protein, moisture content, and $b\ast$ value, but pressure had a significant effect on carotene content. The best treatment was a supercritical CO2 treatment at 1100 psi for 10 min, which was determined based on a significant reduction in the number of microorganisms and no significant changes in color, texture, and fat content were observed compared with control. The best treatment was applied to process shrimps, which were then stored at 4°C to evaluate the effectiveness of scCO2 treatment on the shelf life. No significant changes were found in PV and lipid in treated and scCO2-treated shrimps during storage, but the treatment significantly affected pH, TVBN, and microbial counts. Among the samples, there was no hedonic difference in all sensory attributes. Supercritical CO2 treatment at 1100 psi for 10 min can be an alternative method for preservation of shrimps.

Kinetics and Mechanism of Solvent Influence on the Lipase-Catalyzed 1,3-Diolein Synthesis

1,3-Diacylglycerol preparation has roused increasing attention in recent years as the 1,3-diacylglycerol-rich oils can suppress the deposition of visceral fat and prevent the body weight increasing. Lipozyme TL IM-mediated esterification of oleic acid with monoolein was effective for 1,3-diacylglycerol production. During the esterification process, the solvent shows obvious influence on the diolein synthesis as well as the 1,3-diolein production. This work investigated the related kinetics and mechanism of the solvent effect on the esterification and Lipozyme TL IM performance. The results indicated that both the esterification rate constant and the acyl migration rate constant positively correlated with the logP of the solvent, while the site specificity of lipase has negative correlation with solvent logP. The acylation toward the 2-position of 1-monoolein was more sensitive to the solvent logP compared to the 1-position of glycerides. Molecular dynamics simulation revealed that solvents with different logP influenced the structure of Lipozyme TL IM including RMSD, hydrogen bond, and radial distribution function to a large extent, which subsequently led to the catalytic activity and selectivity variation of the lipase.

High-Pressure Carbon Dioxide Used for Pasteurization in Food Industry

The demand for safe, high-quality food has greatly increased, in recent times. As traditional thermal pasteurization can significantly impact the nutritional value and the color of fresh food, an increasing number of nonthermal pasteurization technologies have attracted attention. The bactericidal effect of high-pressure carbon dioxide has been known for many years, and its effect on food-related enzymes has been studied. This novel technology has many merits, owing to its use of relatively low pressures and temperatures, which make it a potentially valuable future method for nonthermal pasteurization. For example, the inactivation of polyphenol oxidase can be achieved with relatively low temperature and pressure, and this can contribute to food quality and better preserve nutrients, such as vitamin C. However, this novel technology has yet to be developed on an industrial scale due to insufficient test data. In order to support the further development of this application, on an industrial scale, we have reviewed the existing information on high-pressure carbon dioxide pasteurization technology. We include its bactericidal effects and its influence on food quality. We also pave the way for future studies, by highlighting key areas.