Enzyme_Metal-Organic Framework Composites as Novel Approach for Microplastic Degradation

Plastic pollution is one of the main worldwide environmental concerns. Our lifestyle involves persistent plastic consumption, aggravating the low efficiency of wastewater treatment plants in its removal. Nano/microplastics are accumulated in living beings, pushing to identify new water remediation strategies to avoid their harmful effects. Enzymes (e. g., Candida rugosa-CrL) are known natural plastic degraders as catalysts in depolymerization reactions. However, their practical use is limited by their stability, recyclability, and economical concerns. Here, enzyme immobilization in metal-organic frameworks (CrL_MOFs) is originally presented as a new plastic degradation approach to achieve a boosted plastic decomposition in aqueous systems while allowing the catalyst cyclability. Bis-(hydroxyethyl)terephthalate (BHET) was selected as model substrate for decontamination experiments for being the main polyethylene terephthalate (PET) degradation product. Once in contaminated water, CrL_MOFs can eliminate BHET (37 %, 24 h), following two complementary mechanisms: enzymatic degradation (CrL action) and byproducts adsorption (MOF effect). As a proof-of-concept, the capacity of a selected CrL_MOF composite to eliminate the BHET degradation products and its reusability are also investigated. The potential of these systems is envisioned in terms of improving enzyme cyclability, reducing costs along with feasible co-adsorption of plastic byproducts and other harmful contaminants, to successfully remove them in a single step.

Highly effective enzymes immobilization on ceramics: Requirements for supports and enzymes

Enzyme immobilization is a well-known method for the improvement of enzyme reusability and stability. To achieve very high effectiveness of the enzyme immobilization, not only does the method of attachment need to be optimized, but the appropriate support must be chosen. The essential necessities addressed to the support applied for enzyme immobilization can be focused on the material features as well as on the stability and resistances in certain conditions. Ceramic membranes and nanoparticles are the most widespread supports for enzyme immobilization. Hence, the immobilization of enzymes on ceramic membrane and nanoparticles are summarized and discussed. The important properties of the supports are particle size, pore structure, active surface area, volume to surface ratio, type and number of reactive available groups, as well as thermal, mechanical, and chemical stability. The modifiers and the crosslinkers are crucial to the enzyme loading amount, the chemical and physical stability, and the reusability and catalytical activity of the immobilized enzymes. Therefore, the chemical and physical methods of modification of ceramic materials are presented. The most popular and used modifiers (e.g. APTES, CPTES, VTES) as well as activating agents (GA, gelatin, EDC and/or NHS) applied to the grafting process are discussed. Moreover, functional groups of enzymes are presented and discussed since they play important roles in the enzyme immobilization via covalent bonding. The enhanced physical, chemical, and catalytical properties of immobilized enzymes are discussed revealing the positive balance between the effectiveness of the immobilization process, preservation of high enzyme activity, its good stability, and relatively low cost.

Thermal processing implications on the digestibility of meat, fish and seafood proteins

Thermal processing is an inevitable part of the processing and preparation of meat and meat products for human consumption. However, thermal processing techniques, both commercial and domestic, induce modifications in muscle proteins which can have implications for their digestibility. The nutritive value of muscle proteins is closely related to their digestibility in the gastrointestinal tract and is determined by the end products that it presents in the assimilable form (amino acids and small peptides) for the absorption. The present review examines how different thermal processing techniques, such as sous-vide, microwave, stewing, roasting, boiling, frying, grilling, and steam cooking, affect the digestibility of muscle proteins in the gastrointestinal tract. By altering the functional and structural properties of muscle proteins, thermal processing has the potential to influence the digestibility negatively or positively, depending on the processing conditions. Thermal processes such as sous-vide can induce favourable changes, such as partial unfolding or exposure of cleavage sites, in muscle proteins and improve their digestibility whereas processes such as stewing and roasting can induce unfavourable changes, such as protein aggregation, severe oxidation, cross linking or increased disulfide (S-S) content and decrease the susceptibility of proteins during gastrointestinal digestion. The review examines how the underlying mechanisms of different processing conditions can be translated into higher or lower protein digestibility in detail. This review expands the current understanding of muscle protein digestion and generates knowledge that will be indispensable for optimizing the digestibility of thermally processed muscle foods for maximum nutritional benefits and optimal meal planning.

Immobilization of an amino acid racemase for application in crystallization-based chiral resolutions of asparagine monohydrate

Integration of racemization and a resolution process is an attractive way to overcome yield limitations in the production of pure chiral molecules. Preferential crystallization and other crystallization-based techniques usually produce low enantiomeric excess in solution, which is a constraint for coupling with racemization. We developed an enzymatic fixed bed reactor that can potentially overcome these unfavorable conditions and improve the overall yield of preferential crystallization. Enzyme immobilization strategies were investigated on covalent-binding supports. The amino acid racemase immobilized in Purolite ECR 8309F with a load of 35 mg-enzyme/g-support showed highest specific activity (approx. 500 U/g-support) and no loss in activity in reusability tests. Effects of substrate inhibition observed for the free enzyme were overcome after immobilization. A packed bed reactor with the immobilized racemase showed good performance in steady state operation processing low enantiomeric excess inlet. Kinetic parameters from batch reactor experiments can be successfully used for prediction of packed bed reactor performance. Full conversions could be achieved for residence times above 1.1 min. The results suggest the potential of the prepared racemase reactor to be combined with preferential crystallization to improve resolution of asparagine enantiomers.

Immobilization of Aldoxime Dehydratases and Their Use as Biocatalysts in Aqueous Reaction Media

Immobilization of biocatalysts is a current topic in research enabling the easy recovery of catalysts from the reaction medium after the reaction, and it is often accompanied by a stabilization of the catalysts, which enables recycling. Within our ongoing research on the utilization of aldoxime dehydratases in the cyanide-free synthesis of nitriles through dehydration of readily available aldoximes, a screening of different immobilization methods for free enzymes was performed. The applied immobilization methods are based on covalent binding and hydrophobic interactions of the enzyme with the carrier material and whole-cell immobilization in calcium alginate beads with and without subsequent coating. In our study, we found that the immobilization with purified free aldoxime dehydratases from OxdRE (Rhodococcus erythropolis) and OxdB (Bacillus sp. strain OxB-1) leads to high immobilization efficiencies, but also to a strong loss of activity with a residual activity of <20%, regardless of the carrier material used. However, when using whole cells for immobilization instead of purified enzymes, we could increase the residual activity significantly. Escherichia coli BL21(DE3)-CodonPlus-RIL OxdRE and OxdB whole cells were entrapped in calcium alginate beads and coated with silica using tetraethylorthosilicate (TEOS), leading to immobilized catalysts with up to 75% residual activity and a higher stability compared to the free whole cells. Even after three rounds of recycling, which corresponds to a 3 d reaction time, the immobilized OxdB whole cells showed a residual activity of 85%.

Impact of microwave processing on the secondary structure, in-vitro protein digestibility and allergenicity of shrimp (Litopenaeus vannamei) proteins

This study aimed to evaluate the effects of microwave processing (2.45 GHz, 1000 W, 75-125 °C, and 5-15 min) on the secondary structures, in-vitro protein digestibility, microstructural characteristics, and allergenicity of shrimp. SDS-PAGE analysis showed that the band intensity of tropomyosin reduced with the increase of processing temperatures and durations. The significant reduction in the allergenicity of tropomyosin was up to 75% when treated with microwave at 125 °C for 15 min. A significant reduction by 30-75% in the total soluble protein content, peptide content, and in-vitro protein digestibility of shrimp protein was observed. These changes mentioned above were strongly associated with the modification of the secondary structure of shrimp proteins, including the increase in β-sheets, and the loss in turns. Also, more microscopic holes, fragments, strips in treated samples were observed by scanning electron microscopy. Therefore, high-intensity microwave treatment showed great potential in reducing the allergenicity of shrimp.

Microwave processing: Effects and impacts on food components

As an efficient heating method, microwave processing has attracted attention both in academic research and industry. However, the mechanism of dielectric heating is quite distinct from that of the traditional conduction heating, and is widely applied as polar molecules and charged ions interaction with the alternative electromagnetic fields, resulting in fast and volumetric heating through their friction losses. Such a heating pattern would cause a certain change in microwave treatment, which is an unarguable reality. In this review, we made a retrospect of the essential knowledge about dielectric properties and summarized the concept of microwave heating, and the impact of microwave application on the main components of foods and agricultural products, which are classified as carbohydrates, lipids, proteins, chromatic/flavor substances, and vitamins. Finally, we offered a way to resolve the drawbacks of relevant microwave treatment and outlined the directions for future research.