Purification and characterization of neutral protease from Aspergillus oryzae Y1 isolated from naturally fermented broad beans

Valorization of agro-industrial residues using Aspergillus heteromorphus URM0269 for protease production: Characterization and purification

This study aimed to produce, characterize and purify a protease from Aspergillus heteromorphus URM0269. After production by solid fermentation of wheat bran performed according to a central composite design, protease was characterized in terms of biochemical, kinetic, and thermodynamic parameters for further purification by chromatography. Proteolytic activity achieved a maximum value of 57.43 U/mL using 7.8 g of wheat bran with 40 % moisture. Protease displayed high stability in the pH and temperature ranges of 5.0-10.0 and 20-30 °C, respectively, and acted optimally at pH 7.0 and 50 °C. The enzyme, characterized as a serine protease, followed Michaelis-Menten kinetics with a maximum reaction rate of 140.0 U/mL and Michaelis constant of 11.6 mg/mL. Thermodynamic activation parameters, namely activation Gibbs free energy (69.79 kJ/mol), enthalpy (5.86 kJ/mol), and entropy (-214.39 J/mol.K) of the hydrolysis reaction, corroborated with kinetic modeling showing high affinity for azocasein. However, thermodynamic parameters suggested a reversible mechanism of unfolding. Purification by chromatography yielded a protease purification factor of 7.2, and SDS-PAGE revealed one protein band with a molecular mass of 14.7 kDa. Circular dichroism demonstrated a secondary structure made up of 45.6 % α-helices. These results show the great potential of this protease for future use in the industrial area.

Starter molds and multi-enzyme catalysis in koji fermentation of soy sauce brewing: A review

Soy sauce is a traditional fermented food produced from soybean and wheat under the action of microorganisms. The soy sauce brewing process mainly involves two steps, namely koji fermentation and moromi fermentation. In the koji fermentation process, enzymes from starter molds, such as protease, aminopeptidase, carboxypeptidase, l-glutaminase, amylase, and cellulase, hydrolyze the protein and starch in the raw ingredients to produce short-chain substances. However, the enzymatic reactions may be diminished after being subjected to moromi fermentation due to its high NaCl concentration. These enzymatically hydrolyzed products are further metabolized by lactic acid bacteria and yeasts during the moromi fermentation process into organic acids and aromatic compounds, giving soy sauce a unique flavor. Thus, the starter molds, such as Aspergillus oryzae, Aspergillus sojae, and Aspergillus niger, and their secreted enzymes play crucial roles in soy sauce brewing. This review comprehensively covers the characteristics of the starter molds mainly used in soy sauce brewing, the enzymes produced by starter molds, and the roles of enzymes in the degradation of raw material. We also enumerate current problems in the production of soy sauce, aiming to offer some directions for the improvement of soy sauce taste.

Statistical versus neural network-embedded swarm intelligence optimization of a metallo-neutral-protease production: activity kinetics and food industry applications

An integrated approach involving response surface methodology (RSM) and artificial neural network-ant-colony hybrid optimization (ANN-ACO) was adopted to develop a bioprocess medium to increase the yield of Bacillus cereus neutral protease under submerged fermentation conditions. The ANN-ACO model was comparatively superior (predicted r2 = 98.5%, mean squared error [MSE] = 0.0353) to RSM model (predicted r2 = 86.4%, MSE = 23.85) in predictive capability arising from its low performance error. The hybrid model recommended a medium containing (gL-1) molasses 45.00, urea 9.81, casein 25.45, Ca2+ 1.23, Zn2+ 0.021, Mn2+ 0.020, and 4.45% (vv-1) inoculum, for a 6.75-fold increase in protease activity from a baseline of 76.63 UmL-1. Yield was further increased in a 5-L bioreactor to a final volumetric productivity of 3.472 mg(Lh)-1. The 10.0-fold purified 46.6-kDa-enzyme had maximum activity at pH 6.5, 45-55 °C, with Km of 6.92 mM, Vmax of 769.23 µmolmL-1 min-1, kcat of 28.49 s-1, and kcat/Km of 4.117 × 103 M-1 s-1, at 45 °C, pH 6.5. The enzyme was stabilized by Ca2+, activated by Zn2+ but inhibited by EDTA suggesting that it was a metallo-protease. The biomolecule significantly clarified orange and pineapple juices indicating its food industry application.

Microbial-derived salt-tolerant proteases and their applications in high-salt traditional soybean fermented foods: a review

Different microorganisms can produce different proteases, which can adapt to different industrial requirements such as pH, temperature, and pressure. Salt-tolerant proteases (STPs) from microorganisms exhibit higher salt tolerance, wider adaptability, and more efficient catalytic ability under extreme conditions compared to conventional proteases. These unique enzymes hold great promise for applications in various industries including food, medicine, environmental protection, agriculture, detergents, dyes, and others. Scientific studies on microbial-derived STPs have been widely reported, but there has been little systematic review of microbial-derived STPs and their application in high-salt conventional soybean fermentable foods. This review presents the STP-producing microbial species and their selection methods, and summarizes and analyzes the salt tolerance mechanisms of the microorganisms. It also outlines various techniques for the isolation and purification of STPs from microorganisms and discusses the salt tolerance mechanisms of STPs. Furthermore, this review demonstrates the contribution of modern biotechnology in the screening of novel microbial-derived STPs and their improvement in salt tolerance. It highlights the potential applications and commercial value of salt-tolerant microorganisms and STPs in high-salt traditional soy fermented foods. The review ends with concluding remarks on the challenges and future directions for microbial-derived STPs. This review provides valuable insights into the separation, purification, performance enhancement, and application of microbial-derived STPs in traditional fermented foods.

The latest advances on soy sauce research in the past decade: Emphasis on the advances in China

As an indispensable soybean-fermented condiment, soy sauce is extensively utilized in catering, daily cooking and food industry in East Asia and Southeast Asia and is becoming popular in the whole world. In the past decade, researchers began to pay great importance to the scientific research of soy sauce, which remarkably promoted the advances on fermentation strains, quality, safety, function and other aspects of soy sauce. Of them, the screening and reconstruction of Aspergillus oryzae with high-yield of salt and acid-tolerant proteases, mechanism of soy sauce flavor formation, improvement of soy sauce quality through the combination of novel physical processing technique and microbial/enzyme, separation and identification of soy sauce functional components are attracting more attention of researchers, and related achievements have been reported continually. Meanwhile, we pointed out the drawbacks of the above research and the future research directions based on published literature and our knowledge. We believe that this review can provide an insightful reference for international related researchers to understand the advances on soy sauce research.

Enhancement of Growth and Synthesis of Extracellular Enzymes of Morchella sextelata Induced by Co-culturing with Trichoderma

Trichoderma is a genus of common filamentous fungi that display a various range of lifestyles and interactions with other fungi. The interaction of Trichoderma with Morchella sextelata was explored in this study. Trichoderma sp. T-002 was isolated from a wild fruiting body of Morchella sextelata M-001 and identified as a closely related species of Trichoderma songyi based on morphological chracteristics and phylogenetic analysis of translation elongation factor1-alpha and inter transcribed spacer of rDNA. Further, we focussed on the influence of dry mycelia of T-002 on the growth and synthesis of extracellular enzymes of M-001. Among different treatments, M-001 showed the highest growth of mycelia with an optimal supplement of 0.33 g/100 mL of T-002. Activities of extracellular enzymes of M-001 were enhanced significantly by the optimal supplement treatment. Overall, T-002, a unique Trichoderma species, had a positive effect on mycelial growth and synthesis of extracellular enzymes of M-001.

The differences between broad bean koji fermented in laboratory and factory conditions by an efficient Aspergillus oryzae

Broad bean paste-meju was fermented by a mixture of broad bean koji and saline; koji fermentation is an essential process for the production of broad bean paste-meju. Aspergillus oryzae was the most widely used in sauce fermentation. The purpose of this study was to research the factory adaptability of the highly efficient A. oryzae PNM003 and further evaluate the effect of fermentation conditions and fermentation strains on koji. A. oryzae PNM003 was compared with the widely used strain HN 3.042 not only in the laboratory but also in factory conditions (large scale). Results showed that the koji made with the same starter in the factory had a greater amount of fungi than that in the laboratory. Bacteria and yeast levels in HN_L koji were higher than in PN_L koji. As for fungi constitution, almost only Aspergillus survived in the end through the microorganism self-purification process during koji fermentation. As for the bacterial constitution, koji was grouped by fermentation conditions instead of fermentation starter. PN koji had higher protease activity and a higher content of total acids, amino acid nitrogen, amino acids, and organic acids in the laboratory conditions. Nevertheless, in factory conditions, PN koji and HN koji had similar indexes. As for volatile flavor compounds, koji made with the two starters in the same condition was grouped together. As for the same starter, there were more flavor compounds metabolized in the factory condition than in the laboratory condition, especially esters and alcohols. The results showed PN was a highly efficient strain to ferment koji, but the advantages were expressed more remarkably in laboratory conditions. In brief, the fermented condition had a greater influence than the fermentation starter for broad bean koji.

Isolation and Purification of Bacillus amyloliquefaciens D1 Protease and Its Application in the Fermentation of Soybean Milk to Produce Large Amounts of Free Amino Acids

In this study, a strain of Bacillus amyloliquefaciens D1, with a notably high production of neutral protease, was isolated from Morchella crassipes. The protease was purified to 10.4-fold with a specific activity of 4542.9 U/mg and 2.7% recovery. The enzyme was purified by 70% (NH₄)₂SO₄ and DEAE-Cellulose-52 column. The estimated molecular mass of the purified protease obtained by SDS-PAGE was approximately 40 kDa. The enzyme was optimally active at pH 6.0 and 50 °C. Furthermore, the maximum hydrolysis rate (Vmax) and apparent Michaelis-Menten constant (Km) values of the purified protease were 8.2 mg/mL and 65.7 µg/(min mL). The enzymatic properties and rapid and efficient purification of Bacillus amyloliquefaciens D1 provide the basis for its potential commercialization and industrial development. Moreover, more essential amino acids, such as isoleucine, leucine, and phenylalanine, would be released when the strain fermented soybean milk, and then a better amino acid profile would be formed in soybean milk. Results suggest that this strain exhibits great potential in fermented soybean milk, and the enzyme could lay a foundation for its industrial application and further research.

Heterologous Expression of Extracellular Proteinase pAsPs of Aspergillus pseudotamarii in Komagataella phaffii

Neutral protease pAsPs gene was obtained by sequence optimization of NpI protease from Aspergillus pseudotamarii. pAsPs was for the first time integrated in the genome of yeast strain Komagataella phaffii T07, and then produced in a 5 L bioreactor with an enzyme yield of 150,800 U/mL of culture liquid towards casein. The specific activity of the pAsPs was 7,657,000 U/mg toward casein, 2320 U/mg toward hemoglobin, and 25,344 U/mg toward azocasein per 1 mg of the protein. The enzyme was found to be inhibited by Cu²⁺. Optimal activity pH was shown in the range of pH 6.5-8.0, and optimal temperature-50-60 °C. The molecular mass of the recombinant protease pAsPs was shown to be 67.5 kDa. Mass-spectrometric analysis confirmed the identity of the amino acid sequence of the obtained pAsPs preparation with the predicted sequence, with 17% coverage and protein score 288. Thus, the novel neutral protease pAsPs is a promising candidate for large-scale use in manufacturing, including the food industry.

Monitoring the effects of fungi isolated from archival document on model albumen silver prints

Fungi are a common problem in the photographic collection, so the aim of this study focused on isolating and molecular identification of fungi from old albumen prints dating to an archive of Dr. Francis and belonging to the Al-Hagar Family and dating back to 1880-1890. The isolated fungi were identified according to their morphological traits and PCR sequencing. The ability of these isolates to cause deterioration was evaluated on model samples (2 × 2 cm) of albumen silver prints. The effect of these fungi on the morphology and structure of the tested samples were examined by SEM, ATR-FTIR, and chromatic alternations. Four fungal species Aspergillus sydowii, A. flavus, Talaromyces atroroseus, and Penicillium chrysogenum were identified. All isolates were able to grow on the surface of the model Albumen silver print and were capable of causing damage to the binder and able to extend their growth to the paper fibers. A. sydowii, A. flavus, and P. chrysogenum caused hydrolysis and oxidation to the albumen prints, while no significant chemical damage to the albumen was detected for the photographic sample infected with T. atroroseus. All the inoculated samples were significantly affected in terms of color change and the high-light areas have become darker. ATR-FTIR spectra showed the degradation of the protein content in Albumen silver prints inoculated with A. sydowii, A. flavus, and P. chrysogenum.

Study of protease activity from Aspergillus awamori INCQS2B.361U2/1 extracellular fraction and modification of culture medium composition to isolate a novel aspartic protease

Aspergillus awamori was cultivated in a modified Breccia medium, and the extracellular fraction was obtained, which presented 260 ± 15 µg of protein/mg and specific protease activity of 3.87 ± 0.52 mM.min^-1.mg of protein^-1 using N_α-p-tosyl-L-arginine methyl ester hydrochloride (_L-TAME) as substrate. This fraction showed major proteins about 104 and 44 kDa and maximal protease activity at pH 5.5, 6.5, and 9.0, suggesting that A. awamori secretes acidic, neutral, and alkaline proteases with expressive thermal stability, however, aspartic protease was the most important activity. When yeast extract was supplemented to a modified Breccia medium, A. awamori protein secretion and protease activity were maximal and the affinity chromatography on pepstatin-agarose was employed to isolate the aspartic protease activity, which was called ASPA, with approximately 75 kDa. ASPA maximal activity was obtained at pH 4.5 and 6.5, and 50 °C. Pepstatin inhibited about 80% of ASPA activity, with IC₅₀ and Ki values of 0.154 and 0.072 μM, respectively. ASPA cleaved protein and peptides substrates with the highest activity against gelatin (95 U/mg) and good peptidase activity with K_M 0.0589 mM and V_max 1.909 mM.min^-1.mg protein^-1, using _L-TAME as substrate. A. awamori extracellular fraction is a source of proteases with important activity, and the supplementation of modified Breccia medium increased the aspartic protease production. This enzyme presented different biochemical characteristics from the previously reported A. awamori aspartic proteases. Therefore, ASPA is an excellent candidate for biotechnological application due to its important activity and thermostability.

Plant associated endophytic fungi as potential bio-factories for extracellular enzymes: Progress, Challenges and Strain improvement with precision approaches

There is an intricate network of relations between endophytic fungi and their hosts that affects the production of various bioactive compounds. Plant-associated endophytic contain industrially important enzymes and have the potential to fulfill their rapid demand in the international market to boost business in technology. Being safe and metabolically active, they have replaced the usage of toxic and harmful chemicals and hold a credible application in biotransformation, bioremediation, and industrial processes. Despite these, there are limited reports on fungal endophytes that can directly cater to the demand and supply of industrially stable enzymes. The underlying reasons include low endogenous production and secretion of enzymes from fungal endophytes which have raised concern for widely accepted applications. Hence it is imperative to augment the biosynthetic and secretory potential of fungal endophytes. Modern state-of-the-art biotechnological technologies aiming at strain improvement using cell factory engineering as well as precise gene editing like Clustered Regularly Interspaced Palindromic Repeats (CRISPR) and its Associated proteins (Cas) systems which can provide a boost in fungal endophyte enzyme production. Additionally, it is vital to characterize optimum conditions to grow one strain with multiple enzymes (OSME). The present review encompasses various plants-derived endophytic fungal enzymes and their applications in various sectors. Further, we postulate the feasibility of new precision approaches with an aim for strain improvement and enhanced enzyme production.

Fungal Proteases as Emerging Biocatalysts to Meet the Current Challenges and Recent Developments in Biomedical Therapies: An Updated Review

With the increasing world population, demand for industrialization has also increased to fulfill humans' living standards. Fungi are considered a source of essential constituents to produce the biocatalytic enzymes, including amylases, proteases, lipases, and cellulases that contain broad-spectrum industrial and emerging applications. The present review discussed the origin, nature, mechanism of action, emerging aspects of genetic engineering for designing novel proteases, genome editing of fungal strains through CRISPR technology, present challenges and future recommendations of fungal proteases. The emerging evidence revealed that fungal proteases show a protective role to many environmental exposures and discovered that an imbalance of protease inhibitors and proteases in the epithelial barriers leads to the protection of chronic eosinophilic airway inflammation. Moreover, mitoproteases recently were found to execute intense proteolytic processes that are crucial for mitochondrial integrity and homeostasis function, including mitochondrial biogenesis, protein synthesis, and apoptosis. The emerging evidence revealed that CRISPR/Cas9 technology had been successfully developed in various filamentous fungi and higher fungi for editing of specific genes. In addition to medical importance, fungal proteases are extensively used in different industries such as foods to prepare butter, fruits, juices, and cheese, and to increase their shelf life. It is concluded that hydrolysis of proteins in industries is one of the most significant applications of fungal enzymes that led to massive usage of proteomics.

Microbial proteases: ubiquitous enzymes with innumerable uses

Proteases are ubiquitous enzymes, having significant physiological roles in both synthesis and degradation. The use of microbial proteases in food fermentation is an age-old process, which is today being successfully employed in other industries with the advent of ‘omics’ era and innovations in genetic and protein engineering approaches. Proteases have found application in industries besides food, like leather, textiles, detergent, waste management, agriculture, animal husbandry, cosmetics, and pharmaceutics. With the rising demands and applications, researchers are exploring various approaches to discover, redesign, or artificially synthesize enzymes with better applicability in the industrial processes. These enzymes offer a sustainable and environmentally safer option, besides possessing economic and commercial value. Various bacterial and fungal proteases are already holding a commercially pivotal role in the industry. The current review summarizes the characteristics and types of proteases, microbial source, their current and prospective applications in various industries, and future challenges. Promoting these biocatalysts will prove significant in betterment of the modern world.

Extracellular neutral protease from Arthrospira platensis: Production, optimization and partial characterization

Proteases are industrially important catalysts. They belong to a complex family of enzymes that perform highly focused proteolysis functions. Given their potential use, there has been renewed interest in the discovery of proteases with novel properties and a constant thrust to optimize the enzyme production. In the present study, a novel extracellular neutral protease produced from Arthrospira platensis was detected and characterized. Its proteolytic activity was strongly activated by β-mercaptoethanol, 5,5-dithio-bis-(2-nitrobenzoic acid) and highly inhibited by Hg²⁺ and Zn²⁺ metal ions which support the fact that the studied protease belongs to the cysteine protease family. Using statistical modelling methodology, the logistic model has been selected to predict A. platensis growth-kinetic values. The optimal culture conditions for neutral protease production were found using Box-Behnken Design. The maximum experimental protease activities (159.79 U/mL) was achieved after 13 days of culture in an optimized Zarrouk medium containing 0.625 g/L NaCl, 0.625 g/L K₂HPO₄ and set on 9.5 initial pH. The extracellular protease of A. platensis can easily be used in the food industry for its important activity at neutral pH and its low production cost since it is a valuation of the residual culture medium after biomass recovery.

Biochemical characterization of a partially purified protease from Aspergillus terreus 7461 and its application as an environmentally friendly dehairing agent for leather industry

Proteases can be used in several biotechnological processes including detergent, food and leather industries. In the leather industry, dehairing is carried out by chemicals, which pollute the environment. Therefore, to make the hair removal process environmentally friendly, a protease produced by Aspergillus terreus has been purified, biochemically characterized and had an efficient ability to remove hair from bovine leather. The protease was produced using 1% wheat bran and was purified 2.3-fold using two chromatographic steps showing a molecular weight of 90 kDa. Optimal temperature and pH were 50 °C and 6.5, respectively. Thermal stability was up to 1 h at 50 °C. Protease was stable to detergents like Tween 80 and to organic solvents. The activity was activated by Ca²⁺ and inhibited by Hg²⁺ and Cu²⁺. The enzyme was classified as serine protease, by the inhibition by PMSF and was stable to reducing agents. It hydrolyzed casein, azocasein, BSA, egg albumin and BTpNA. The Km and Vmax values were 0.65 ± 0.03 mg/mL and 3.66 ± 0.18 μmol/min, respectively. Remarkable properties about temperature, pH, stability to detergents and reducing agents ensure that the protease from A. terreus can be an excellent candidate for industrial applications, particularly in the leather industry.

Lys-Arg mutation improved the thermostability of Bacillus cereus neutral protease through increased residue interactions

Neutral proteases have broad application as additives in modern laundry detergents and therefore, thermostability is an integral parameter for effective production of protein crystals. To improve thermostability, the contribution of individual residues of Bacillus cereus neutral protease was examined by site-directed mutagenesis. The Lys11Arg and Lys211Arg mutants clearly possessed improved thermostabilities (T_m were 63 and 61 °C respectively) compared to the wild-type (T_m was 60 °C). MD simulations further revealed that the mutants had low RMSD and RMSF values compared to wild-type BCN indicating increased stability of the protein structure. Lys11Arg mutant particularly possessed the lowest RMSD values due to increased residue interactions, which resulted in enhanced thermostability. The mutants also displayed strong stability to most inhibitors, organic solvents and surfactants after incubation for 1 h. This study demonstrated Lys-Arg mutation enhanced thermostability of BCN and thus provides insight for engineering stabilizing mutations with improved thermostability for related proteins.

Purification and characterization of a propanol-tolerant neutral protease from Bacillus sp. ZG20

A propanol-tolerant neutral protease was purified and characterized from Bacillus sp. ZG20 in this study. This protease was purified to homogeneity with a specific activity of 26,655 U/mg. The recovery rate and purification fold of the protease were 13.7% and 31.5, respectively. The SDS-PAGE results showed that the molecular weight of the protease was about 29 kDa. The optimal temperature and pH of the protease were 45 °C and 7.0, respectively. The protease exhibited a good thermal- and pH stability, and was tolerant to 50% propanol. Mg²⁺, Zn²⁺, K⁺, Na⁺ and Tween-80 could improve its activity. The calculated K_m and V_max values of the protease towards α-casein were 12.74 mg/mL and 28.57 µg/(min mL), respectively. This study lays a good foundation for the future use of the neutral protease from Bacillus sp. ZG20.

Multidisciplinary involvement and potential of thermophiles

The full biotechnological exploitation of thermostable enzymes in industrial processes is necessary for their commercial interest and industrious value. The heat-tolerant and heat-resistant enzymes are a key for efficient and cost-effective translation of substrates into useful products for commercial applications. The thermophilic, hyperthermophilic, and microorganisms adapted to extreme temperatures (i.e., low-temperature lovers or psychrophiles) are a rich source of thermostable enzymes with broad-ranging thermal properties, which have structural and functional stability to underpin a variety of technologies. These enzymes are under scrutiny for their great biotechnological potential. Temperature is one of the most critical parameters that shape microorganisms and their biomolecules for stability under harsh environmental conditions. This review describes in detail the sources of thermophiles and thermostable enzymes from prokaryotes and eukaryotes (microbial cell factories). Furthermore, the review critically examines perspectives to improve modern biocatalysts, its production and performance aiming to increase their value for biotechnology through higher standards, specificity, resistance, lowing costs, etc. These thermostable and thermally adapted extremophilic enzymes have been used in a wide range of industries that span all six enzyme classes. Thus, in particular, target of this review paper is to show the possibility of both high-value-low-volume (e.g., fine-chemical synthesis) and low-value-high-volume by-products (e.g., fuels) by minimizing changes to current industrial processes.