Rice husk ash as a potential carrier for the immobilization of lipases applied in the enzymatic production of biodiesel

Latest Trends in Lipase-Catalyzed Synthesis of Ester Carbohydrate Surfactants: From Key Parameters to Opportunities and Future Development

Carbohydrate-based surfactants are amphiphilic compounds containing hydrophilic moieties linked to hydrophobic aglycones. More specifically, carbohydrate esters are biosourced and biocompatible surfactants derived from inexpensive renewable raw materials (sugars and fatty acids). Their unique properties allow them to be used in various areas, such as the cosmetic, food, and medicine industries. These multi-applications have created a worldwide market for biobased surfactants and consequently expectations for their production. Biobased surfactants can be obtained from various processes, such as chemical synthesis or microorganism culture and surfactant purification. In accordance with the need for more sustainable and greener processes, the synthesis of these molecules by enzymatic pathways is an opportunity. This work presents a state-of-the-art lipase action mode, with a focus on the active sites of these proteins, and then on four essential parameters for optimizing the reaction: type of lipase, reaction medium, temperature, and ratio of substrates. Finally, this review discusses the latest trends and recent developments, showing the unlimited potential for optimization of such enzymatic syntheses.

Renewable, sustainable, and natural lignocellulosic carriers for lipase immobilization: A review

It is well-known that enzymes are molecules particularly susceptible to pH and temperature variations. Immobilization techniques may overcome this weakness besides improving the reusability of the biocatalysts. Given the strong push toward a circular economy, the use of natural lignocellulosic wastes as supports for enzyme immobilization has been increasingly attractive in recent years. This fact is mainly due to their high availability, low costs, and the possibility of reducing the environmental impact that can occur when they are improperly stored. In addition, they have physical and chemical characteristics suitable for enzyme immobilization (large surface area, high rigidity, porosity, reactive functional groups, etc.). This review aims to guide readers and provide them with the tools necessary to select the most suitable methodology for lipase immobilization on lignocellulosic wastes. The importance and the characteristics of an increasingly interesting enzyme, such as lipase, and the advantages and disadvantages of the different immobilization methods will be discussed. The various kinds of lignocellulosic wastes and the processing required to make them suitable as carriers will be also reported.

Agro-Industrial Food Waste as a Low-Cost Substrate for Sustainable Production of Industrial Enzymes: A Critical Review

The grave environmental, social, and economic concerns over the unprecedented exploitation of non-renewable energy resources have drawn the attention of policy makers and research organizations towards the sustainable use of agro-industrial food and crop wastes. Enzymes are versatile biocatalysts with immense potential to transform the food industry and lignocellulosic biorefineries. Microbial enzymes offer cleaner and greener solutions to produce fine chemicals and compounds. The production of industrially important enzymes from abundantly present agro-industrial food waste offers economic solutions for the commercial production of value-added chemicals. The recent developments in biocatalytic systems are designed to either increase the catalytic capability of the commercial enzymes or create new enzymes with distinctive properties. The limitations of low catalytic efficiency and enzyme denaturation in ambient conditions can be mitigated by employing diverse and inexpensive immobilization carriers, such as agro-food based materials, biopolymers, and nanomaterials. Moreover, revolutionary protein engineering tools help in designing and constructing tailored enzymes with improved substrate specificity, catalytic activity, stability, and reaction product inhibition. This review discusses the recent developments in the production of essential industrial enzymes from agro-industrial food trash and the application of low-cost immobilization and enzyme engineering approaches for sustainable development.

Lignocellulosic residues as supports for enzyme immobilization, and biocatalysts with potential applications

Growing demand for agricultural production means a higher quantity of residues produced. The reuse and recycling of agro-industrial wastes reduce worldwide greenhouse emissions. New opportunities are derived from this kind of residuals in the biotechnological field generating valuable products in growing sectors such as transportation, bioenergy, food, and feedstock. The use of natural macromolecules towards biocatalysts offers numerous advantages over free enzymes and friendliness with the environment. Enzyme immobilization improves enzyme properties (stability and reusability), and three types of supports are discussed: inorganic, organic, and hybrid. Several examples of agro-industrial wastes such as coconut wastes, rice husks, corn residues and brewers spent grains (BSG), their properties and potential as supports for enzyme immobilization are described in this work. Before the immobilization, biological and non-biological pretreatments could be performed to enhance the waste potential as a carrier. Additionally, immobilization methods such as covalent binding, adsorption, cross-linking and entrapment are compared to provide high efficiency. Enzymes and biocatalysts for industrial applications offer advantages over traditional chemical processes with respect to sustainability and process efficiency in food, energy, and bioremediation fields. The wastes reviewed in this work demonstrated a high affinity for lipases and laccases and might be used in biodiesel production and textile wastewater treatment, among other applications.

Sustainable biodiesel generation through catalytic transesterification of waste sources: a literature review and bibliometric survey

Sustainable renewable energy production is being intensely disputed worldwide because fossil fuel resources are declining gradually. One solution is biodiesel production via the transesterification process, which is environmentally feasible due to its low-emission diesel substitute. Significant issues arising with biodiesel production are the cost of the processes, which has stuck its sustainability and the applicability of different resources. In this article, the common biodiesel feedstock such as edible and non-edible vegetable oils, waste oil and animal fats and their advantages and disadvantages were reviewed according to the Web of Science (WOS) database over the timeframe of 1970-2020. The biodiesel feedstock has water or free fatty acid, but it will produce soap by reacting free fatty acids with an alkali catalyst when they present in high portion. This reaction is unfavourable and decreases the biodiesel product yield. This issue can be solved by designing multiple transesterification stages or by employing acidic catalysts to prevent saponification. The second solution is cheaper than the first one and even more applicable because of the abundant source of catalytic materials from a waste product such as rice husk ash, chicken eggshells, fly ash, red mud, steel slag, and coconut shell and lime mud. The overview of the advantages and disadvantages of different homogeneous and heterogeneous catalysts is summarized, and the catalyst promoters and prospects of biodiesel production are also suggested. This research provides beneficial ideas for catalyst synthesis from waste for the transesterification process economically, environmentally and industrially.

Constitutive Expression in Komagataella phaffii of Mature Rhizopus oryzae Lipase Jointly with Its Truncated Prosequence Improves Production and the Biocatalyst Operational Stability

Rhizopus oryzae lipase (ROL) containing 28 C-terminal amino acids of the prosequence fused to the N-terminal mature sequence in ROL (proROL) was successfully expressed in the methylotrophic yeast Komagataella phaffii (Pichia pastoris) under the constitutive glyceraldehyde-3-phosphate dehydrogenase promoter (PGAP). Although the sequence encoding the mature lipase (rROL) was also transformed, no clones were obtained after three transformation cycles, which highlights the importance of the truncated prosequence to obtain viable transformed clones. Batch cultures of the K. phaffii strain constitutively expressing proROL scarcely influenced growth rate and exhibited a final activity and volumetric productivity more than six times higher than those obtained with proROL from K. phaffii under the methanol-inducible alcohol oxidase 1 promoter (PAOX1). The previous differences were less marked in fed-batch cultures. N-terminal analysis confirmed the presence of the 28 amino acids in proROL. In addition, immobilized proROL exhibited increased tolerance of organic solvents and an operational stability 0.25 and 3 times higher than that of immobilized rROL in biodiesel and ethyl butyrate production, respectively. Therefore, the truncated prosequence enables constitutive proROL production, boosts bioprocess performance and provides a more stable biocatalyst in two reactions in which lipases are mostly used at industrial level, esterification (ethyl butyrate) and transesterification (biodiesel).

Progress in Enzymatic Biodiesel Production and Commercialization

Enzymatic biodiesel production has attracted tremendous interest due to its well-recognized advantages. However, high enzyme costs limit the application of enzymatic processes in industrial production. In the past decade, great improvements have been achieved in the lab and the industrial scale, and the production cost of the enzymatic process has been reduced significantly, which has led to it being economically competitive compared to the chemical process. This paper summarizes the progress achieved in enzymatic biodiesel research and commercialization, including reducing enzyme cost, expanding low-quality raw materials, and novel reactor designs. The advantages and disadvantages of different enzymatic processes are also compared.

Rhizopus oryzae Lipase, a Promising Industrial Enzyme: Biochemical Characteristics, Production and Biocatalytic Applications

Lipases are biocatalysts with a significant potential to enable a shift from current pollutant manufacturing processes to environmentally sustainable approaches. The main reason of this prospect is their catalytic versatility as they carry out several industrially relevant reactions as hydrolysis of fats in water/lipid interface and synthesis reactions in solvent-free or non-aqueous media such as transesterification, interesterification and esterification. Because of the outstanding traits of Rhizopus oryzae lipase (ROL), 1,3-specificity, high enantioselectivity and stability in organic media, its application in energy, food and pharmaceutical industrial sector has been widely studied. Significant advances have been made in the biochemical characterisation of ROL particularly in how its activity and stability are affected by the presence of its prosequence. In addition, native and heterologous production of ROL, the latter in cell factories like Escherichia coli, Saccharomyces cerevisiae and Komagataella phaffii (Pichia pastoris), have been thoroughly described. Therefore, in this review, we summarise the current knowledge about R. oryzae lipase (i) biochemical characteristics, (ii) production strategies and (iii) potential industrial applications.

Environmental impact of lignocellulosic wastes and their effective exploitation as smart carriers - A drive towards greener and eco-friendlier biocatalytic systems

In recent years, lignocellulosic wastes have gathered much attention due to increasing economic, social, environmental apprehensions, global climate change and depleted fossil fuel reserves. The unsuitable management of lignocellulosic materials and related organic wastes poses serious environmental burden and causes pollution. On the other hand, lignocellulosic wastes hold significant economic potential and can be employed as promising catalytic supports because of impressing traits such as surface area, porous structure, and occurrence of many chemical moieties (i.e., carboxyl, amino, thiol, hydroxyl, and phosphate groups). In the current literature, scarce information is available on this important and highly valuable aspect of lignocellulosic wastes as smart carriers for immobilization. Thus, to fulfill this literature gap, herein, an effort has been made to signify the value generation aspects of lignocellulosic wastes. Literature assessment spotlighted that all these waste materials display high potential for immobilizing enzyme because of their low cost, bio-renewable, and sustainable nature. Enzyme immobilization has gained recognition as a highly useful technology to improve enzyme properties such as catalytic stability, performance, and repeatability. The application of carrier-supported biocatalysts has been a theme of considerable research, for the past three decades, in the bio-catalysis field. Nonetheless, the type of support matrix plays a key role in the immobilization process due to its influential impact on the physicochemical characteristics of the as-synthesized biocatalytic system. In the past, an array of various organic, inorganic, and composite materials has been used as carriers to formulate efficient and stable biocatalysts. This review is envisioned to provide recent progress and development on the use of different agricultural wastes (such as coconut fiber, sugarcane bagasse, corn and rice wastes, and Brewers' spent grain) as support materials for enzyme immobilization. In summary, the effective utilization of lignocellulosic wastes to develop multi-functional biocatalysts is not only economical but also reduce environmental problems of unsuitable management of organic wastes and drive up the application of biocatalytic technology in the industry.

Agro-industrial wastes as potential carriers for enzyme immobilization: A review

This review provides a general overview of the suitability of different agro-industrial wastes for enzyme immobilization. For the purposes of this literary study, the support materials are divided into two main groups, called lignocellulosic (coconut fiber, corn cob, spent grain, spent coffee, husk, husk ash, and straw rice, soybean and wheat bran) and not lignocellulosic by-products (eggshell and eggshell membranes). The study pointed out that all of these wastes are materials of great potentiality for enzyme immobilization even if coconut fiber is preferred. This result is of significant interest due to the low cost and great availability of such wastes, which actually are underused and cause significant environmental problems for improper storage. In addition, the development of economic biocatalysts more sustainable, besides reduce environmental impacts, improve the application of enzymatic technology in industry. Therefore, the enzyme immobilization reaction and the application of biocatalysts are reviewed and discussed.

Enzymatic Production of Biodiesel Using Immobilized Lipase on Core-Shell Structured Fe3O4@MIL-100(Fe) Composites

In this research, core–shell structured Fe3O4@MIL-100(Fe) composites were prepared by coating Fe3O4 magnetite with porous MIL-100(Fe) metal-organic framework (MOF) material, which were then utilized as magnetic supports for the covalent immobilization of the lipase from Candida rugosa through amide linkages. By using the carbodiimide/hydroxysulfosuccinimide (EDC/NHS) activation strategy, the lipase immobilization efficiency could reach 83.1%, with an activity recovery of 63.5%. The magnetic Fe3O4@MIL-100(Fe) composite and immobilized lipase were characterized by several techniques. The characterization results showed that the Fe3O4 core was coated with MIL-100(Fe) shell with the formation of perfect core–shell structured composites, and moreover, the lipase was covalently tethered on the magnetic carrier. The immobilized lipase displayed a strong magnetic response and could be facilely separated by an external magnetic field. With this magnetic biocatalyst, the maximum biodiesel conversion attained 92.3% at a methanol/oil molar ratio of 4:1, with a three-step methanol addition manner, and a reaction temperature of 40 °C. Moreover, the biocatalyst prepared in the present study was recycled easily by magnetic separation without significant mass loss, and displayed 83.6% of its initial activity as it was reused for five runs, thus allowing its potential application for the cleaner production of biodiesel.

Recent advances on pollutants removal by rice husk as a bio-based adsorbent: A critical review

Rice husk is an attractive bio-based adsorbent material for pollutant removal since it is one of the low-cost and renewable resources. The objective of this review is to give a summary of the key scientific features related to pollutants removal using rice husk, with a specific emphasis on the effect of factors on adsorption capacity of rice husk. According to the results, rice husk has the removal potential of various pollutants and it can be more used in the wastewater treatment. On the other hand, untreated bio-based adsorbent in large-scale application can usually cause some difficulties and selection of appropriate pretreatment method for rice husk is also one of the major challenges. Therefore, this review studies different pretreatment methods as well as regeneration of adsorbent and the fate of adsorbed contaminants. According to the literature, pretreatment methods increase the rice husk capability and adsorption capacity and the chemical treatments have been more used than thermal treatments. Also, regeneration of rice husk adsorbent and adsorbed contaminants is applicable. Finally, examples of some applications and possibility of biocatalyst immobilization on the rice husk as a promising approach are presented. Results confirmed that rice husk has an excellent prospective potential for biocatalysts immobilization.

Cost analysis of oil cake-to-biodiesel production in packed-bed micro-flow reactors with immobilized lipases

Biodiesel production depends to a great extent on the use of cheap raw materials, since biodiesel itself is a mass product, not a high-value product. New processing methods, such as micro-flow continuous processing combined with enzymatic catalysis, open doors to the latter. As reported here, the window of opportunity in enzyme-catalyzed biodiesel production is the conversion of waste cooking oil. The main technological challenge for this is to obtain efficient immobilization of the lipase catalyst on beads. The beads can be filled into tubular reactors where designed packed-bed provide porous channels, forming micro-flow. It turns out, that in this way, the immobilization costs become the decisive economic factor. This paper reports a solution to that issue. The use of oil cake enables economic viability, which is not given by any of the commercial polymeric substrates used so far for enzyme immobilization. The costs of immobilization are mirrored in the earnings and cash flow of the new biotechnological process.