Production and characterization of a milk-clotting enzyme from Aspergillus oryzae MTCC 5341

Protein secretion and associated stress in industrially employed filamentous fungi

Application of filamentous fungi for the production of commercial enzymes such as amylase, cellulase, or xylanase is on the rise due to the increasing demand to degrade several complex carbohydrates as raw material for biotechnological processes. Also, protein production by fungi for food and feed gains importance. In any case, the protein production involves both cellular synthesis and secretion outside of the cell. Unfortunately, the secretion of proteins or enzymes can be hampered due to accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) as a result of too high synthesis of enzymes or (heterologous) protein expression. To cope with this ER stress, the cell generates a response known as unfolded protein response (UPR). Even though this mechanism should re-establish the protein homeostasis equivalent to a cell under non-stress conditions, the enzyme expression might still suffer from repression under secretory stress (RESS). Among eukaryotes, Saccharomyces cerevisiae is the only fungus, which is studied quite extensively to unravel the UPR pathway. Several homologs of the proteins involved in this signal transduction cascade are also found in filamentous fungi. Since RESS seems to be absent in S. cerevisiae and was only reported in Trichoderma reesei in the presence of folding and glycosylation inhibitors such as dithiothreitol and tunicamycin, more in-depth study about this mechanism, specifically in filamentous fungi, is the need of the hour. Hence, this review article gives an overview on both, protein secretion and associated stress responses in fungi. KEY POINTS: • Enzymes produced by filamentous fungi are crucial in industrial processes • UPR mechanism is conserved among many fungi, but mediated by different proteins • RESS is not fully understood or studied in industrially relevant filamentous fungi.

Production of milk-coagulating protease by fungus Pleurotus djamor through solid state fermentation using wheat bran as the low-cost substrate

Proteases are enzymes that hydrolyze peptide bonds present in proteins and peptides. They are widely used for various industrial applications, such as in the detergent, food, and dairy industries. Cheese is one of the most important products of the dairy industry, and the coagulation stage is crucial during the cheese-making process. Enzymatic coagulation is the most common technique utilized for this purpose. Microbial enzymes are frequently used for coagulation due to their advantages in terms of availability, sustainability, quality control, product variety, and compliance with dietary and cultural/religious requirements. In the present study, we identified and subsequently characterized milk coagulant activity from the fungus Pleurotus djamor PLO13, obtained during a solid-state fermentation process, using the agro-industrial residue, wheat bran, as the fermentation medium. Maximum enzyme production and caseinolytic activity occurred 120 h after cultivation. When the enzyme activity against various protease-specific synthetic substrates and inhibitors was analyzed, the enzyme was found to be a serine protease, similar to elastase 2. This elastase-2-like serine protease was able to coagulate pasteurized whole and reconstituted skim milk highly efficiently in the presence and absence of calcium, even at room temperature. The coagulation process was influenced by factors such as temperature, time, and calcium concentration. We demonstrate here, for the first time, an elastase-2-like enzyme in a microorganism and its potential application in the food industry for cheese production.

Exploring fishery waste potential as antifouling component

Marine biofouling is a global issue with economic and ecological implications. Existing solutions, such as biocide-based antifouling paints, are toxic for the environment. The search for better antifouling agents remains crucial. Recent research focuses on eco-friendly antifouling paints containing natural compounds like enzymes. This study evaluates enzymatic extracts from fishery residues for antifouling potential. Extracts from Pleoticus muelleri shrimp, Illex argentinus squid, and Lithodes santolla king crab were analyzed. Proteolytic activity and thermal stability were assessed, followed by bioassays on mussel byssus thread formation and barnacle cypris adhesive footprints. All three extracts demonstrated proteolytic activity and 24-h stability at temperate oceanic temperatures, except I. argentinus. P. muelleri extracts hindered cyprid footprint formation and mussel byssus thread generation. Further purification is required for L. santolla extract to assess its antifouling potential activity. This study introduces the use of fishery waste-derived enzyme extracts as a novel antifouling agent, providing a sustainable tool to fight against biofouling formation.

Protease production and molecular characterization of a protease dipeptidyl-aminopeptidase gene from different strains of Sordaria fimicola

The current research was designed to reach extracellular protease production potential in different strains of Sordaria fimicola which were previously obtained from Dr. Lamb (Imperial College, London) from North Facing Slope and South Facing Slope of Evolution Canyon. After initial and secondary screening, two hyper-producers strains S2 and N6 were selected for submerged fermentation and cultural conditions including temperature, pH, incubation period, inoculum size, substrate concentration, and different carbon and nitrogen sources were optimized for enzyme production. S2 strain showed maximum protease production of 3.291 U/mL after 14 days of incubation at 30 °C with 7 pH, 1% substrate concentration and 1 mL inoculum, While N6 strain showed maximum protease production of 1.929 U/mL under fermentation optimized conditions. Another aim of the present research was to underpin the biodiversity of genetics and post-translational modifications (PTMs) of protease DPAP (peptidyl-aminopeptidase) in Sordaria fimicola. Five polymorphic sites were observed in amino acid sequence of S. fimicola strains with reference to Neurospora crassa. PTMs prediction from bioinformatics tools predicted 38 phosphorylation sites on serine residues for protease peptidyl-aminopeptidase in S1 strain of S. fimicola while 45 phosphorylation sites on serine in N7 strain and 47 serine phosphorylation modifications were predicted in N. crassa. Current research gave an insight that change in genetic makeup effected PTMs which ultimately affected the production of protease enzyme in different strains of same organism (S. fimicola). The production and molecular data of the research revealed that environmental stress has strong effects on the specific genes through mutations which may cause genetic diversity. S. fimicola is non- pathogenic fungus and has a short life cycle. This fungus can be chosen to produce protease enzyme on a commercial scale.

A novel milk-clotting enzyme from Aspergillus oryzae and A. luchuensis is an aspartic endopeptidase PepE presumed to be a vacuolar enzyme

Aspergillus oryzae RIB40 has 11 aspartic endopeptidase genes. We searched for milk-clotting enzymes based on the homology of the deduced amino acid sequence with chymosins. As a result, we identified a milk-clotting enzyme in A. oryzae. We expected other Aspergillus species to have a homologous enzyme with milk-clotting activity, and we found the most homologous aspartic endopeptidase from A. luchuensis had milk-clotting activity. Surprisingly, 2 enzymes were considered as vacuole enzymes according to a study on A. niger proteases. The 2 enzymes from A. oryzae and A. luchuensis cleaved a peptide between the 105Phe-106Met bond in κ-casein, similar to chymosin. Although both enzymes showed proteolytic activity using casein as a substrate, the optimum pH values for milk-clotting and proteolytic activities were different. Furthermore, the substrate specificities were highly restricted. Therefore, we expected that the Japanese traditional fermentation agent, koji, could be used as an enzyme source for cheese production.

Milk-clotting properties on bovine caseins of a novel cysteine peptidase from germinated Moringa oleifera seeds

A cysteine peptidase was previously identified from germinated Moringa oleifera seeds, but its milk-clotting properties on bovine caseins was still unclear. In this study, this novel cysteine peptidase (MoCP) showed preferential activity on κ-casein (κ-CN), with greater hydrolytic activity compared with calf rennet, whereas weak hydrolysis of α-casein and β-casein made MoCP suitable for application in cheesemaking and may yield various functional peptides. All 3 evaluated caseins were hydrolyzed to form relatively stable peptide bands within 3 h of proteolysis with MoCP. Cleavage sites were determined by gel electrophoresis, liquid chromatography mass spectrometry/mass spectrometry, and peptide sequencing, which revealed that cleavage of κ-CN by MoCP occurred at residue Ile129-Pro130 and generated a 14,895.37-Da peptide. The flocculation reaction between MoCP and κ-CN determined by 3-dimensional microscopy with super-depth of field revealed that the initial 30 min of reaction were key for milk coagulation, which may affect curd yield. Overall, the findings presented herein suggest that the cysteine peptidase from germinated M. oleifera seeds can be considered a promising plant-derived rennet alternative for use in cheese manufacture.

Characterization of a Novel Aspartic Protease from Rhizomucor miehei Expressed in Aspergillus niger and Its Application in Production of ACE-Inhibitory Peptides

Rhizomucor miehei is an important fungus that produces aspartic proteases suitable for cheese processing. In this study, a novel aspartic protease gene (RmproB) was cloned from R. miehei CAU432 and expressed in Aspergillus niger. The amino acid sequence of RmproB shared the highest identity of 58.2% with the saccharopepsin PEP4 from Saccharomyces cerevisiae. High protease activity of 1242.2 U/mL was obtained through high density fermentation in 5 L fermentor. RmproB showed the optimal activity at pH 2.5 and 40 °C, respectively. It was stable within pH 1.5-6.5 and up to 45 °C. RmproB exhibited broad substrate specificity and had K_m values of 3.16, 5.88, 5.43, and 1.56 mg/mL for casein, hemoglobin, myoglobin, and bovine serum albumin, respectively. RmproB also showed remarkable milk-clotting activity of 3894.1 SU/mg and identified the cleavage of Lys21-Ile22, Leu32-Ser33, Lys63-Pro64, Leu79-Ser80, Phe105-Met106, and Asp148-Ser149 bonds in κ-casein. Moreover, duck hemoglobin was hydrolyzed by RmproB to prepare angiotensin-I-converting enzyme (ACE) inhibitory peptides with high ACE-inhibitory activity (IC₅₀ of 0.195 mg/mL). The duck hemoglobin peptides were further produced at kilo-scale with a yield of 62.5%. High-level expression and favorable biochemical characterization of RmproB make it a promising candidate for cheese processing and production of ACE-inhibitory peptides.

Purification and characterization of a protease from Aspergillus sydowii URM5774: Coffee ground residue for protease production by solid state fermentation

Solid state fermentation is a promising technology largely used in biotechnology process and is a suitable strategy for producing low-cost enzymatic products. At the present study, a novel enzyme obtained through solid state fermentation using Aspergillus sydowii was herein purified and characterized. The fermentations used coffee ground residue as substrate and the crude enzyme was submitted through further purification steps of: acetonic precipitation, DEAE-Sephadex and Superdex G-75 column. Both crude and purified enzymes were submitted to biochemical characterization of their thermostability, optimal temperature and pH, effects of inhibitors and metal ions. A purified protease was obtained with yield of 5.9-fold and 53% recovery, with maximal proteolytic activity of 352.0 U/mL. SDS-PAGE revealed a band of protein at 47.0 kDa. The enzyme activity was abolished in the presence of phenyl-methyl sulfonyl fluoride and partially inhibited against Triton X-100 (78.0%). The optimal activity was found in pH 8.0 at 45°C of temperature. Besides, the enzyme showed stability between 35°C and 50°C. It was possible to determine appropriate conditions to the obtainment of thermostable proteases with biotechnological interest associated with a method that concomitantly shows excellent production levels and recovery waste raw material in a very profitable process.

Structural Analysis of a Novel Aspartic-Type Endopeptidase from Moringa oleifera Seeds and Its Milk-Clotting Properties

A novel aspartic-type endopeptidase was previously obtained from Moringa oleifera seeds; however, its specific milk-clotting properties have remained unclear. Here, we used various biophysical and molecular simulation approaches for characterizing the structure and function of the aspartic-type endopeptidase. The endopeptidase was preferentially active toward κ-casein (CN) and hydrolyzed it more than calf rennet; however, its ability to hydrolyze α-CN and β-CN was weaker than that of calf rennet. The endopeptidase cleaved κ-CN at Gln135-Asp136 and generated a 15 588.18 Da peptide with 135 amino acids. We further simulated the docking complex of the endopeptidase and κ-CN and found out that they possibly combined with each other via hydrogen bonds. The flocculation reaction between the endopeptidase and κ-CN indicated that milk coagulation occurred within 60 min. Overall, our observations suggest that the aspartic-type endopeptidase can be a potential rennet alternative for cheese making.

Production, Optimization, and Characterization of an Acid Protease from a Filamentous Fungus by Solid-State Fermentation

Acid proteases represent an important group of enzymes, extensively used in food and beverage industries. There is an increased demand for acid proteases adapting to the industrial extreme environment, especially lower pH. Thus, this necessitates the search for a better acid protease from fungi that best performs in industrial conditions. The fungal isolates were isolated from grape and dairy farm soil using potato dextrose agar and further screened for protease production based on the hydrolysis of clear zone on skim milk agar. The potential fungi were then subjected to secondary screening under solid-state fermentation (SSF). After the secondary screening, the potential fungus was identified to the genus level by the macroscopic and microscopic methods. The growth conditions and media composition for the potential fungus were further optimized under SSF. The crude enzyme produced by the potential isolate was characterized after partial purification by acetone and ammonium sulfate precipitation. A total of 9 fungal isolates showed protease production in primary and secondary screening; however, one potential isolate (Z1BL1) was selected for further study based on its protease activity. The isolate was identified to the genus Aspergillus based on their morphological features. The maximum acid protease from the isolate Z1BL1 was obtained using fermentation media containing wheat bran as a solid substrate, 1 mL of 3.2 × 10⁶ inoculum size, 50% moisture content, and pH 4.5 upon 120-h incubation at 30°C. The acetone-precipitated enzyme exhibited the maximum activity at 50°C and pH 5 with stability at pH 4–6 and temperature 40–60°C. Thus, the acid protease produced from Aspergillus showed suitable enzyme characteristics required in the industry and could be a candidate for application in the food industry after further purification.

Effect of fermentation time and acid casein concentration as nitrogen source on microbial rennet production

We evaluated the effects of fermentation time and acid casein content on the microbial rennet obtained by solid-state fermentation using wheat bran as the carbon source. The experiments used two fermentation times (72 and 96 h), while acid casein content was 1.5, 2.0, 2.5, and 3.0 g. Rennet strength from eight enzymatic extracts was measured using pasteurized whole milk. Rennet strength of samples from 72 h of fermentation showed an increase when acid casein content increased. The rennet strength increased at 96 h of fermentation with increasing amount of casein (up to 2.5 g), and then decreased with the largest addition (3.0 g) of casein. Coagulation time for the sample with highest rennet strength was 420 s.

Optimization of media composition and growth conditions for production of milk-clotting protease (MCP) from Aspergillus oryzae DRDFS13 under solid-state fermentation

This study reports the optimization of milk-clotting protease production from Aspergillus oryzae DRDFS13 under solid-state fermentation (SSF) in both one-variable-at-a-time and response surface methodology (RSM). The production and optimization of milk-clotting protease obtained from Aspergillus oryzae DRDFS13 under solid-state fermentation (SSF) using different agro-industrial wastes as solid substrates were studied. The agro-industrial wastes used included wheat bran, rice bran, pea bran, and grass pea bran. The chemical composition of the best solid substrate was tested using standard methods. Others cultivation parameters were studied, and the results showed that the optimum fermentation medium composed of wheat bran, casein (1% w/w), and glucose (0.5% w/w) and the conditions for maximum milk-clotting protease production were at the moisture content of 55.0%, inoculum of 0.5*10⁶ spores/mL, incubation temperature of 30 °C, pH of 6.0, and fermentation time of 5 days. The highest milk-clotting activity was obtained from the crude enzyme extracted using 0.1 M NaCl and partial purification of the crude enzyme using chilled acetone, and 80% (NH₄)₂SO₄ increased the ratio of MCA/PA from 0.56 to 1.30 and 0.65, respectively. Moreover, the highest MCA (137.58 U/mL) was obtained at a casein concentration of 0.5%, pH 4.0, and 25 °C, using RSM. Thus, results from the present study showed that the optimization of milk-clotting protease production from A. oryzae DRDFS 13 under SSF by both one-variable-at-a-time and RSM significantly increased the milk-clotting activity. This is the first report from a fungus in the Ethiopian setting and a modest contribution to highlight the potential of harnessing microbial protease enzymes for industrial applications.

Production of highly active fungal milk-clotting enzyme by solid-state fermentation

Cheese production is projected to reach 20 million metric tons by 2020, of which 33% is being produced using calf rennet (EC 3.4.23.4). There is shortage of calf rennet, and use of plant and microbial rennets, hydrolyze milk proteins non-specifically resulting in low curd yields. This study reports fungal enzymes obtained from cost effective medium, with minimal down streaming, whose activity is comparable with calf and Mucor rennet. Of the fifteen fungi that were screened, Mucor thermohyalospora (MTCC 1384) and Rhizopus azygosporus (MTCC 10195) exhibited the highest milk-clotting activity (MCA) of 18,383 ± 486 U/ml and 16,373 ±  558 U/ml, respectively. Optimization exhibited a 33% increase in enzyme production (30 g wheat bran containing 6% defatted soy meal at 30 °C, pH 7) for M. thermohyalospora. The enzyme was active from pH 5-10 and temperature 45-55 °C. Rhizopus azygosporus exhibited 31% increase in enzyme production (30 g wheat bran containing 4% defatted soy meal at 30 °C, pH 6) and the enzyme was active from pH 6-9 at 50 °C. Curd yields prepared from fungal enzyme extract decreased (5-9%), when compared with calf rennet and Mucor rennet. This study describes the potential of fungal enzymes, hitherto unreported, as a viable alternative to calf rennet.

Change of proteolysis and sensory profile during ripening of Cheddar-style cheese as influenced by a microbial rennet from rice wine

To test the potential of a novel microbial rennet isolated from traditional fermented rice wine for cheese making, Cheddar-style cheese made with this enzyme was studied for changes in composition, proteolysis, and sensory profile during 90 days of ripening in comparison with a control cheese made with a commercial rennet. The initial proteolysis assay of the microbial rennet on milk proteins indicated a notable increase in the hydrolysis of casein components (α-, β-, and κ-caseins) but no effect on whey proteins upon increasing the concentration of the enzyme. Correspondingly, compared to cheese made with commercial rennet, the use of the microbial rennet in Cheddar-style cheese resulted in significantly higher primary and secondary proteolysis in the later stages of ripening (60-90 days ripening) and thus a softer texture and the formation of more volatile compounds and free amino acids (FAAs) despite its lower moisture content (41.7%, w/w). Though the cheese made with the microbial rennet was found to contain bitter-taste FAAs (1,000 mg/100 g), the combined effect of other-taste FAAs, including sweet (231 mg/100 g), umami (225 mg/100 g), and tasteless (361 mg/100 g) FAAs, in the cheese attenuated the bitter taste of the cheese. This analysis was in accordance with the sensory evaluation, which showed no significantly different sensory scoring between the cheeses made with the microbial and commercial rennets. The present study demonstrated a novel approach to evaluate the bitter taste of ripened cheese. The results of this study suggest the potential of the microbial rennet from rice wine to serve as a new source of milk-clotting agents in cheese making.

Response Surface Methodology Optimization of an Acidic Protease Produced by Penicillium bilaiae Isolate TDPEF30, a Newly Recovered Endophytic Fungus from Healthy Roots of Date Palm Trees (Phoenix dactylifera L.)

To explore proteolytic activity of endophytic fungi inhabiting date palm roots, a Penicillium bilaiae isolate, displaying the highest level of protease production, has been recovered. Response surface methodology (RSM) was applied to optimize culture conditions for protease production by the fungus. Plackett-Burman design allowed for screening of variables effective in protease production. Results indicated that temperature, initial pH and glucose concentration dramatically affect protease yield. These factors were further optimized using a Box-Behnken design and RSM. A combination of initial pH (6.26), temperature (24.5 °C), glucose (13.75 g/L), NaNO₃ (1.5 g/L), MgSO₄ (0.2 g/L), KH₂PO₄ (0.5 g/L) and KCl (0.5 g/L) were optimum for maximum production of protease. A 1086-fold enhancement of protease production was gained after optimization. Biochemical properties of fungal protease including the effect of pH and temperature on the activity and the stability of proteolytic enzyme were determined. Moreover, the influence of carbon and nitrogen sources, metal ions, detergents as well as enzyme inhibitors was investigated. Our results highlighted that protease of Penicillium bilaiae isolate TDPEF30 could be considered as a promising candidate for industrial applications.

Enzymes of industrial interest

For many years, industrial enzymes have played an important role in the benefit of our society due to their many useful properties and a wide range of applications. They are key elements in the progress of many industries including foods, beverages, pharmaceuticals, diagnostics, therapy, personal care, animal feed, detergents, pulp and paper, textiles, leather, chemicals and biofuels. During recent decades, microbial enzymes have replaced many plant and animal enzymes. This is because microbial enzymes are widely available and produced economically in short fermentations and inexpensive media. Screening is simple, and strain improvement for increased production has been very successful. The advances in recombinant DNA technology have had a major effect on production levels of enzymes and represent a way to overproduce industrially important microbial, plant and animal enzymes. It has been calculated that 50-60% of the world enzyme market is supplied with recombinant enzymes. Molecular methods, including genomics and metagenomics, are being used for the discovery of new enzymes from microbes. Also, directed evolution has allowed the design of enzyme specificities and better performance.

Diversity, Application, and Synthetic Biology of Industrially Important Aspergillus Fungi

The filamentous fungal genus Aspergillus consists of over 340 officially recognized species. A handful of these Aspergillus fungi are predominantly used for food fermentation and large-scale production of enzymes, organic acids, and bioactive compounds. These industrially important Aspergilli primarily belong to the two major Aspergillus sections, Nigri and Flavi. Aspergillus oryzae (section Flavi) is the most commonly used mold for the fermentation of soybeans, rice, grains, and potatoes. Aspergillus niger (section Nigri) is used in the industrial production of various enzymes and organic acids, including 99% (1.4 million tons per year) of citric acid produced worldwide. Better understanding of the genomes and the signaling mechanisms of key Aspergillus species can help identify novel approaches to enhance these commercially significant strains. This review summarizes the diversity, current applications, key products, and synthetic biology of Aspergillus fungi commonly used in industry.

Simultaneous lactic acidification and coagulation by using recombinant Lactococcus lactis strain

AIMS

This study was an attempt to create a novel milk clotting procedure using a recombinant bacterium capable of milk coagulation.

METHODS AND RESULTS

The Rhizomucor pusillus proteinase (RPP) gene was sub-cloned into a pALF expression vector. The recombinant pALF-RPP vector was then electro-transferred into Lactococcus lactis. Finally, the milk coagulation ability of recombinant L. lactis carrying a RPP gene was evaluated. Nucleotide sequencing of DNA insertion from the clone revealed that the RPP activity corresponded to an open reading frame consisting of 1218 bp coding for a 43·45 kDa RPP protein. The RPP protein assay results indicated that the highest RPP enzyme expression with 870 Soxhlet units (SU) per ml and 7914 SU/OD were obtained for cultures which were incubated at pH 5·5 and 30°C. Interestingly, milk coagulation was observed after 205 min of inoculating milk with recombinant L. lactis carrying the RPP gene.

CONCLUSION

The recombinant L. lactis carrying RPP gene has the ability to function as a starter culture for acidifying and subsequently coagulating milk by producing RPP as a milk coagulant agent.

SIGNIFICANCE AND IMPACT OF THE STUDY

Creating a recombinant starter culture bacterium that is able to coagulate milk. It is significant because the recombinant L. lactis has the ability to work as a starter culture and milk coagulation agent.

Cloning and Expression of Yak Active Chymosin in Pichia pastoris

Rennet, a complex of enzymes found in the stomachs of ruminants, is an important component for cheese production. In our study, we described that yak chymosin gene recombinant Pichia pastoris strain could serve as a novel source for rennet production. Yaks total RNA was extracted from the abomasum of an unweaned yak. The yak preprochymosin, prochymosin, and chymosin genes from total RNA were isolated using gene specific primers based on cattle chymosin gene sequence respectively and analyzed their expression pattern byreal time-polymerase chain reaction. The result showed that the chymosin gene expression level of the sucking yaks was 11.45 times higher than one of adult yaks and yak chymosin belongs to Bovidae family in phylogenetic analysis. To express each, the preprochymosin, prochymosin, and chymosin genes were ligated into the expression vector pPICZαA, respectively, and were expressed in Pichia pastoris X33. The results showed that all the recombinant clones of P. pastoris containing the preprochymosin, prochymosin or chymosin genes could produce the active form of recombinant chymosin into the culture supernatant. Heterologous expressed prochymosin (14.55 Soxhlet unit/mL) had the highest enzyme activity of the three expressed chymosin enzymes. Therefore, we suggest that the yak chymosin gene recombinant Pichia pastoris strain could provide an alternative source of rennet production.

High Milk-Clotting Activity Expressed by the Newly Isolated Paenibacillus spp. Strain BD3526

Paenibacillus spp. BD3526, a bacterium exhibiting a protein hydrolysis circle surrounded with an obvious precipitation zone on skim milk agar, was isolated from raw yak (Bos grunniens) milk collected in Tibet, China. Phylogenetic analysis based on 16S rRNA and whole genome sequence comparison indicated the isolate belong to the genus Paenibacillus. The strain BD3526 demonstrated strong ability to produce protease with milk clotting activity (MCA) in wheat bran broth. The protease with MCA was predominantly accumulated during the late-exponential phase of growth. The proteolytic activity (PA) of the BD3526 protease was 1.33-fold higher than that of the commercial R. miehei coagulant. A maximum MCA (6470 ± 281 SU mL⁻¹) of the strain BD3526 was reached under optimal cultivation conditions. The protease with MCA was precipitated from the cultivated supernatant of wheat bran broth with ammonium sulfate and purified by anion-exchange chromatography. The molecular weight of the protease with MCA was determined as 35 kDa by sodium dodecyl sulfate-polyacrylamide gels electrophoresis (SDS-PAGE) and gelatin zymography. The cleavage site of the BD3526 protease with MCA in κ-casein was located at the Met₁₀₆–Ala₁₀₇ bond, as determined by mass spectrometry analysis.

A biotechnology perspective of fungal proteases

Proteases hydrolyze the peptide bonds of proteins into peptides and amino acids, being found in all living organisms, and are essential for cell growth and differentiation. Proteolytic enzymes have potential application in a wide number of industrial processes such as food, laundry detergent and pharmaceutical. Proteases from microbial sources have dominated applications in industrial sectors. Fungal proteases are used for hydrolyzing protein and other components of soy beans and wheat in soy sauce production. Proteases can be produced in large quantities in a short time by established methods of fermentation. The parameters such as variation in C/N ratio, presence of some sugars, besides several other physical factors are important in the development of fermentation process. Proteases of fungal origin can be produced cost effectively, have an advantage faster production, the ease with which the enzymes can be modified and mycelium can be easily removed by filtration. The production of proteases has been carried out using submerged fermentation, but conditions in solid state fermentation lead to several potential advantages for the production of fungal enzymes. This review focuses on the production of fungal proteases, their distribution, structural-functional aspects, physical and chemical parameters, and the use of these enzymes in industrial applications.

Production and characterization of a milk-clotting protease produced in submerged fermentation by the thermophilic fungus Thermomucor indicae-seudaticae N31

Proteases are some of the most important industrial enzymes, and one of their main applications is for the production of cheese in the dairy industry. Due to a shortage of animal rennet, microbial coagulant proteases are being sought. In this work, the production of microbial rennet from Thermomucor indicae-seudaticae N31 was studied in submerged fermentation. The best enzyme production was obtained in a fermentation medium containing 4 % wheat bran as the substrate in 0.3 % saline solution, incubated for 72 h at 45 °C and 150 rpm. The value of the milk clotting activity (MCA) was 60.5 U/mL, and the ratio to proteolytic activity (MCA/PA) was 510. The crude enzyme showed optimum pH at 5.5 and two peaks of optimum temperature (MCA at 65 °C and PA at 60 °C). The MCA was stable in the pH range 4.0-4.5 for 24 h and up to 55 °C for 1 h. It was stable during storage at different temperatures (-20 to 25 °C) for 10 weeks. Based on these results, we conclude that microbial rennet from T. indicae-seudaticae N31 produced by submerged fermentation showed good prospects of replacing traditional rennet.

Yield, changes in proteolysis, and sensory quality of Prato cheese produced with different coagulants

The objective of this research was to compare the effect of 2 fungal proteases, one that is already commercially established as a milk-clotting agent and another produced at the laboratory scale, on Prato cheese composition, protein and fat recovery, yield, and sensory characteristics. Cheeses were produced according to the traditional protocol, using protease from the fungus Thermomucor indicae-seudaticae N31 and commercial coagulant from Rhizomucor spp. as clotting agents. A 2×6 factorial design with 3 replications was performed: 2 levels of coagulants and 6 levels of storage time. After 5, 12, 19, 33, 43, and 53d of refrigerated storage (12°C), cheeses were monitored for proteolysis, firmness, and casein degradation by capillary electrophoresis. Sensory acceptance was evaluated after 29d of manufacturing. The different coagulants did not statistically affect Prato cheese composition, protein and fat recovery, and yield. Both cheeses presented good sensory acceptance. Proteolysis increased and firmness decreased for both cheeses during the storage time, as expected for Prato cheese. Caseins were well separated by capillary electrophoresis and the results showed, with good resolution, that the cheeses exhibited similar protein hydrolysis profile. Both cheeses presented good sensory acceptance. The gathered data showed that the protease from T. indicae-seudaticae N31 presented similar action compared with the commercial enzyme, indicating its efficiency as clotting agent for Prato cheese manufacture.

Biochemical study of the extracellular aspartyl protease Eap1 from the phytopathogen fungus Sporisorium reilianum

In this work, the extracellular protease Eap1 from Sporisorium reilianum was characterized in solid and liquid cultures using different culture media. The results showed that Eap1 was produced in all media and under all culture conditions, with the most activity in solid culture at an acidic pH of 3-5. Following purification, the 41 kDa protease demonstrated aspartyl protease activity. The enzyme was stable at a wide range of temperatures and pH values, but 45°C and pH 3 were optimal. The K(m) and V(max( values obtained were 0.69 mg/mL and 0.66 μmol/min, respectively, with albumin as the substrate. Eap1 degraded hemoglobin as well as proteins obtained from corn germ, roots, stems and slides at pH 3 and also had milk-clotting activity. Sequencing analysis showed that this protein has 100% similarity to the peptide sequence theoretically obtained from the sr11394 gene, which encodes an aspartyl protease secreted by S. reilianum.

Optimization of the production and characterization of milk clotting enzymes by Bacillus subtilis natto

Suitable medium for production of milk clotting enzyme (MCE) by Bacillus subtilis (natto) Takahashi in submerged liquid-state fermentation was screened, the nutrient factors affecting MCE production was optimized by response surface methodology. The MCE production by B. subtilis (natto) Takahashi was increased significantly by 428% in the optimal medium developed. The MCE was filtered and concentrated by ultrafiltration. The retentate after tandem filtration carried out with the combined membranes of MWCO 50kDa and 5 kDa showed two major bands between 25kDa and 30kDa on SDS-PAGE, and the MCA and MCA/PA improved significantly in comparison with those in the initial broth. The crude enzyme thus obtained showed MCA and MCA/PA ratio of 48,000 SU/g and 6,400, which are commensurate with those (MCA 26,667 SU/g and MCA/PA 6,667) of the commercial rennet. It had optimal pH and temperature at pH 6 and 60°C, and showed excellent pH and thermal stability.