Use of Nanomaterials-Based Enzymes in the Food Industry

Natural enzymes, exquisite biocatalysts mediating every biological process in living organisms, are able to accelerate the rate of chemical reactions up to 10(19) times for specific substrates and reactions. However, the practical application of enzymes is often hampered by their intrinsic drawbacks, such as low operational stability, sensitivity of catalytic activity to environmental conditions, and high costs in preparation and purification. Therefore, the discovery and development of artificial enzymes is highly desired. Recently, the merging of nanotechnology with biology has ignited extensive research efforts for designing functional nanomaterials that exhibit various properties intrinsic to enzymes. As a promising candidate for artificial enzymes, catalytically active nanomaterials (nanozymes) show several advantages over natural enzymes, such as controlled synthesis in low cost, tunability in catalytic activities, as well as high stability against stringent conditions. In this Account, we focus on our recent progress in exploring and constructing such nanoparticulate artificial enzymes, including graphene oxide, graphene-hemin nanocomposites, carbon nanotubes, carbon nanodots, mesoporous silica-encapsulated gold nanoparticles, gold nanoclusters, and nanoceria. According to their structural characteristics, these enzyme mimics are categorized into three classes: carbon-, metal-, and metal-oxide-based nanomaterials. We aim to highlight the important role of catalytic nanomaterials in the fields of biomimetics. First, we provide a practical introduction to the identification of these nanozymes, the source of the enzyme-like activities, and the enhancement of activities via rational design and engineering. Then we briefly describe new or enhanced applications of certain nanozymes in biomedical diagnosis, environmental monitoring, and therapeutics. For instance, we have successfully used these biomimetic catalysts as colorimetric probes for the detection of cancer cells, nucleic acids, proteins, metal ions, and other small molecules. In addition, we also introduce three exciting advances in the use of efficient modulators on artificial enzyme systems to improve the catalytic performance of existing nanozymes. For example, we report that graphene oxide could serve as a modulator to greatly improve the catalytic activity of lysozyme-stabilized gold nanoclusters at neutral pH, which will have great potential for applications in biological systems. We show that, through the incorporation of modulator into artificial enzymes, we can offer a facile but highly effective way to improve their overall catalytic performance or realize the catalytic reactions that were not possible in the past. We expect that nanozymes with unique properties and functions will attract increasing research interest and lead to new opportunities in various fields of research.

This critical review provides an overview of current research on carbon-based nanostructured materials and their composites for use as supercapacitor electrodes. Particular emphasis has been directed towards basic principles of supercapacitors and various factors affecting their performance. The focus of the review is the detailed discussion regarding the performance and stability of carbon-based materials and their composites. Pseudo-active species, such as, conducting polymer/metal oxide have been found to exhibit pseudo-capacitive behavior and carbon-based materials demonstrate electrical double layer capacitance. Carbon-based materials, such as, graphene, carbon nanotubes, and carbon nanofibers, provide high surface area for the deposition of conducting polymer/metal oxide that facilitates the efficient ion diffusion phenomenon and contribute towards higher specific capacitance of the carbon based composite materials with excellent cyclic stability. However, further scope of research still exists from the view point of developing high energy supercapacitor devices in a cost effective and simple way. This review will be of value to researchers and emerging scientists dealing with or interested in carbon chemistry.

The bactericide is one of the major objective consequences related to healthcare in the world. Natural enzymes have been broadly utilized in various applications such as biomedical areas due to their broad catalytic activities and substrate particularity. While anticipating, it has drawbacks like higher cost, low stability, and troubles in reprocessing. Additionally, artificial enzymes (nanozymes) have favors above natural enzymes, for example, the effortless yield on a big scale, low costs, and high stability in coarse surrounds. The amount of antibiotic repellent microorganisms has activated big concern in the growth of stuff with essential bactericide potentials such as metal or metal oxide nanoparticles, cationic polymeric compounds, graphene oxide, and other carbon materials that can be used as antibacterial agents by altering cell morphology. In this report, we have summarized catalytic antibacterial strategies by natural enzymes, artificial enzymes, or photocatalytic activity. Furthermore, the demands and hereafter contents about catalytic antibacterial strategies are supposed in this report.

Natural enzymes play vital roles in biological reactions in living systems. However, some intrinsic drawbacks, such as ease of denaturation, laborious preparation, high cost, and difficulty of recycling, have limited their practical applications. To tackle these problems, intensive efforts have been devoted to developing natural enzymes’ alternatives called “artificial enzymes.” As an emerging research area of artificial enzymes, nanozymes, the catalytic nanomaterials with enzyme-like characteristics, have attracted researchers’ enormous attentions. In this chapter, after the brief description of the history of nanozymes research in the course of natural enzymes and artificial enzymes research, a comparison between nanozymes and natural enzymes as well as artificial enzymes is made. Such a comparison highlights the unique characteristics of nanozymes, such as their size-(shape-, structure-, composition-)tunable catalytic activities, large surface area for modification and bioconjugation, multiple functions besides catalysis, smart response to external stimuli, etc.

5 - Current and future uses of enzymes in food processing

Enzyme mimics or artificial enzymes are a class of catalysts that have been actively pursued for decades and have heralded much interest as potentially viable alternatives to natural enzymes. Aside from having catalytic activities similar to their natural counterparts, enzyme mimics have the desired advantages of tunable structures and catalytic efficiencies, excellent tolerance to experimental conditions, lower cost, and purely synthetic routes to their preparation. Although still in the midst of development, impressive advances have already been made. Enzyme mimics have shown immense potential in the catalysis of a wide range of chemical and biological reactions, the development of chemical and biological sensing and anti-biofouling systems, and the production of pharmaceuticals and clean fuels. This Review concerns the development of various types of enzyme mimics, namely polymeric and dendrimeric, supramolecular, nanoparticulate and proteinic enzyme mimics, with an emphasis on their synthesis, catalytic properties and technical applications. It provides an introduction to enzyme mimics and a comprehensive summary of the advances and current standings of their applications, and seeks to inspire researchers to perfect the design and synthesis of enzyme mimics and to tailor their functionality for a much wider range of applications.

Review: 301 refs.

Simple Design of an Enzyme-Inspired Supported Catalyst Based on a Catalytic Triad

Advanced nanostructured carbon-based materials for rechargeable lithium-sulfur batteries

Bacterial infection continues to be a growing global health problem with the most widely accepted treatment paradigms restricted to antibiotics. However, antibiotics overuse and misuse have triggered increased multidrug resistance, frustrating the therapeutic outcomes and leading to higher mortalities. Even worse, the tendency of bacteria to form biofilms on living and nonliving surfaces further increases the difficulty in confronting bacteria because the extracellular matrix can act as a robust barrier to prevent the penetration of antibiotics and resist environmental stress. As a result, the inability to completely eliminate bacteria and biofilms often leads to persistent infection, implant failure, and device damage. Therefore, it is of paramount importance to develop alternative antimicrobial agents while avoiding the generation of bacterial resistance. Taking lessons from natural enzymes for destroying cellular structural integrity or interfering with metabolisms such as proliferation, quorum sensing, and programmed death, the construction of artificial enzymes to mimic the enzyme functions will provide unprecedented opportunities for combating bacteria. Moreover, compared to natural enzymes, artificial enzymes possess much higher stability against stringent conditions, easier tunable catalytic activity, and large-scale production for practical use. In this Account, we will focus on our recent progress in the design and synthesis of artificial enzymes as a new generation of "antibiotics", which have been demonstrated as promising applications in planktonic bacteria inactivation, wound/lung disinfection, as well as biofilm inhibition and dispersion. First, we will introduce direct utilization of the intrinsic catalytic activities of artificial enzymes without dangerous chemical auxiliaries for killing bacteria under mild conditions. Second, to avoid the toxicity caused by overdose of H2O2 in conventional disinfections, we leveraged artificial enzymes with peroxidase-mimic activities to catalyze the generation of hydroxyl radicals at low H2O2 levels while achieving efficient antibacterial outcomes. Importantly, the feasibility of these artificial enzymes was further demonstrated in vivo by mitigating mice wound and lung disinfection. Third, by combining artificial enzymes with stimuli-responsive materials, smart on-demand therapeutic modalities were constructed for thwarting bacteria in a controllable manner. For instance, a photoswitchable "Band-Aid"-like hydrogel doped with artificial enzymes was developed for efficiently killing bacteria without compromising mammal cell proliferation, which was promising for accelerating wound healing. Lastly, regarding the key roles that extracellular DNAs (eDNAs) play in maintaining biofilm integrity, we further designed a multinuclear metal complex-based DNase-mimetic artificial enzyme toward cleaving the eDNA for inhibiting biofilm formation and dispersing the established biofilms. We expect that our rational designs would boost the development of artificial enzymes with different formulations as novel antibacterial agents for clinical and industrial applications.

Fungi and bacteria cause foodborne diseases and affect food security, which remains the main challenge of the global food industry. Nanomaterials-based enzyme (NMB) technologies play an important role in improving food security issues. This is possible since they can act quickly and efficiently on food substrates when used as biosensors to monitor and control the quality and shelf life of food. This chapter deals primarily with the applications of NMB in the food industry. The production, properties, and applications of nano-enzymes of carbon, zinc oxide, magnetite, copper, and some noble metals in the food industry were discussed. It was suggested that the material could mimic catalytic activities and compete with other naturally occurring enzymes, such as hydrolase and oxidoreductase in foods. It is hoped that this chapter will provide key insights into NMB technologies applied in the food industry.

Tuning the enzyme-like activity and studying the interaction between biologically relevant species and nano-enzymes may facilitate the applications of nanostructures in mimicking natural enzymes. In this work, AuPt alloy nanoparticles (NPs) with varying compositions were prepared through a facile method by co-reduction of Au3+ and Pt2+ in aqueous solutions. The composition could be tuned easily by adjusting the molar ratios of added Pt2+ to Au3+. It was found that both peroxidase-like and oxidase-like activity of AuPt alloy NPs were highly dependent on the alloy compositions, which thus suggesting an effective way to tailor their catalytic properties. By investigating the inhibitory effects of HS− on the enzyme-like activity of AuPt alloy NPs and natural enzyme, we have developed a method for colorimetric detection of HS− and evaluation of the inhibiting effects of inhibitors on natural and artificial enzymes. In addition, the responsive ability of this method was influenced largely by the composition: AuPt alloy NPs show much lower limit of detection for HS− than Pt NPs while Pt NPs show wider linear range than AuPt alloy NPs. This study suggests the facile way not only for synthesis of alloy nanostructures, but also for tuning their catalytic activities and for use in bioanalysis.

The use of enzymes such as rennet in cheese making and barley amylases in brewing is as old as the food and beverage industry itself. However, the production of the amylase represents the first example of the industrial production of an enzyme for use in the food industry. The quantity and variety of enzymes used in the food and beverage industry has increased dramatically in the past decade. (Godfrey and Reichelt, 1983; Peppler and Reed, 1987). More than 20 different enzymes are regularly used in the food and beverage industry at the present time. Some of those are shown in Table 8.1. The conversion of starch to different commercial products, such as glucose and maltose syrups and dextrin preparations, represents the major application of food enzymes (Fig. 8.1) having a market value in excess of $100 million in 1988 (West, 1988). The use of enzymes in the dairy industry for cheese making and for the production of low lactose dairy products is the second largest market at $65 million.

Enzymes are proteins that facilitate or accelerate biochemical reactions. While enzymes can be produced from animals, plants or microbes, most of the enzymes used in industry at commercial scale are produced from microbial fermentation due to the ease of multiplication of these microbes and their handling. The two fermentation technologies used in production of enzymes are solid substrate fermentation and submerged fermentation. In solid substrate fermentations, microorganisms are cultivated on a solid substrate whereas in submerged fermentation, they are cultivated in a liquid medium containing nutrients. Post fermentation, enzymes are recovered using downstream processing. Downstream processing constitutes of basic processes such as enzyme separation from cells, it's purification, concentration, and formulation. Enzymes have been used in food industry since pre-historic times. With the increased demand to find sustainable alternatives that enable higher efficiency and increased yields, there has been a rise in application of enzymes in industry. Enzymes are employed in various food processing sectors including baking, starch processing, brewing, dairy industry and many more. The safety assessment of enzymes is the key consideration while evaluating its application in industry. The global organizations that are in safety evaluation are IPCS and JECFA. JECFA uses the guideline “Environmental Health Criteria 240” in safety assessment of enzymes. Some of the specific safety concerns identified by JECFA are allergenicity, safety of enzymes derived from genetically modified microorganisms, toxicological considerations, dietary exposure. JECFA has also classified enzymes as type I and Type II depending on safety of their sources. Global regulatory framework with respect of usage of enzymes in food industry is very diverse and still evolving. The enzymes that are used as food additives are listed in Codex standard of food additives whereas the enzymes that are used as processing aids are governed by Codex guidelines on substances used as processing aids. India also follows a similar approach in regulating enzymes depending on their use, i.e. whether they are used an additive or as a processing aid.

Natural enzymes, such as biocatalysts, are widely used in biosensors, medicine and health, the environmental field, and other fields. However, it is easy for natural enzymes to lose catalytic activity due to their intrinsic shortcomings including a high purification cost, insufficient stability, and difficulties of recycling, which limit their practical applications. The unexpected discovery of the Fe3O4 nanozyme in 2007 has given rise to tremendous efforts for developing natural enzyme substitutes. Nanozymes, which are nanomaterials with enzyme-mimetic catalytic activity, can serve as ideal candidates for artificial mimic enzymes. Nanozymes possess superiorities due to their low cost, high stability, and easy preparation. Although great progress has been made in the development of nanozymes, the catalytic efficiency of existing nanozymes is relatively low compared with natural enzymes. It is still a challenging task to develop nanozymes with a precise regulation of catalytic activity. This review summarizes the classification and various strategies for modulating the activity as well as research progress in the different application fields of nanozymes. Typical examples of the recent research process of nanozymes will be presented and critically discussed.