Purification and characterization milk-clotting aspartic proteinases from Centaurea calcitrapa cell suspension cultures

Protease from banana stem postharvest (Musa x paradisiaca): Extraction, purification, and its potential milk-clotting activity

Plant protease isolation has gained significant attention, particularly from agricultural waste, due to its promising potential for economic enhancement, sustainability, and greenness. While a previous study has focused on protease production from banana peels, the postharvest stem of bananas remains underexplored, which is more abundant as waste. This study aimed to extract and purify protease from the postharvest stems of banana (Musa x paradisiaca), investigating various factors influencing its activity. We optimized protease extraction using different pH buffer solutions and purified the enzyme through three-phase partitioning (TPP). Molecular weight analysis was conducted using SDS-PAGE, and the protease classification was determined using specific protease inhibitors. Optimal conditions for enzyme activity were determined concerning pH, temperature, metal ion effects, organic solvent effects, salinity, and storage conditions. The results indicated that the best extraction pH was 8.0, with purified proteases exhibiting molecular weights of approximately 18 kDa and 21 kDa, classified as serine proteases. Specific metal ions enhanced protease activity, while Ca2+ and Na+ negatively impacted it. Furthermore, the milk clotting activity (MCA) to protease activity (PA) ratio was notably higher compared to other reported plant coagulants, suggesting the potential of this novel protease from banana stems as a milk coagulant.

Production of Plant Proteases and New Biotechnological Applications: An Updated Review

An updated review of emerging plant proteases with potential biotechnological application is presented. Plant proteases show comparable or even greater performance than animal or microbial proteases for by-product valorization through hydrolysis for, for example, cheese whey, bird feathers, collagen, keratinous materials, gelatin, fish protein, and soy protein. Active biopeptides can be obtained as high added value products, which have shown numerous beneficial effects on human health. Plant proteases can also be used for wastewater treatment. The production of new plant proteases is encouraged for the following advantages: low cost of isolation using simple procedures, remarkable stability over a wide range of operating conditions (temperature, pH, salinity, and organic solvents), substantial affinity to a broad variety of substrates, and possibility of immobilization. Vegetable proteases have enormous application potential for the valorization of industrial waste and its conversion into products with high added value through low-cost processes.

Tobacco BY2 cells expressing recombinant cardosin B as an alternative for production of active milk clotting enzymes

Cynara cardunculus L. or cardoon is a plant that is used as a source of milk clotting enzymes during traditional cheese manufacturing. This clotting activity is due to aspartic proteases (APs) found in the cardoon flower, named cyprosins and cardosins. APs from cardoon flowers display a great degree of heterogeneity, resulting in variable milk clotting activities and directly influencing the final product. Producing these APs using alternative platforms such as bacteria or yeast has proven challenging, which is hampering their implementation on an industrial scale. We have developed tobacco BY2 cell lines as an alternative plant-based platform for the production of cardosin B. These cultures successfully produced active cardosin B and a purification pipeline was developed to obtain isolated cardosin B. The enzyme displayed proteolytic activity towards milk caseins and milk clotting activity under standard cheese manufacturing conditions. We also identified an unprocessed form of cardosin B and further investigated its activation process. The use of protease-specific inhibitors suggested a possible role for a cysteine protease in cardosin B processing. Mass spectrometry analysis identified three cysteine proteases containing a granulin-domain as candidates for cardosin B processing. These findings suggest an interaction between these two groups of proteases and contribute to an understanding of the mechanisms behind the regulation and processing of plant APs. This work also paves the way for the use of tobacco BY2 cells as an alternative production system for active cardosins and represents an important advancement towards the industrial production of cardoon APs.

Potential utility of callus proteases as a milk clotting alternative to naturally propagated Wrightia tinctoria proteases

This study was intended to understand suitability of Wrightia tinctoria calli proteases (CCE) as vegetable coagulant through delineating their milk clotting potential and casein (whole and κ-casein) hydrolysis pattern in comparison to their plant stem crude enzyme (PSCE), rennin and Enzeco^® (positive controls). Stem calli was induced using two concentrations of naphthalene acetic acid (NAA) [0.5 mg/L (M1), 1 mg/L (M2)] with fixed concentration (1 mg/L) of 6-benzylaminopurine (BAP). Healthy calli, with significant growth at the end of 14th, 28th, and 48th days, were chosen for enzyme extraction. Overall activity calculated as per gram of fresh weight of callus revealed 3-fold high milk clotting index (MCI) by 28th day CCE in comparison to PSCE (p < 0.5). 14th day CCE mimicked rennin, 28th day CCE partially mimicked rennin and Enzeco^® in their casein hydrolytic pattern. 28th day CCE however exhibited a closer similarity to rennin in its κ- casein hydrolytic pattern. 48th day CCE (M1) presented high MCA, however, with low MCI in comparison to other CCEs. High affinity toward caseins similar to that of Enzeco^® was observed from 48th day CCE. Results from this study indicate 28th day callus protease may serve as a prospective vegetable milk coagulant alternative.

Proteomics analysis of the bio-functions of Dregea sinensis stems provides insights regarding milk-clotting enzyme

Dregea sinensis (D. sinensis) stems have traditionally been used as milk coagulant in Dali of Yunnan Province, China. In this study, proteomics was used to investigate the bio-functions of D. sinensis stem proteins, leading to the purification and identification of the milk-clotting enzyme. A total of 205 proteins mainly involved in the catalytic and metabolic processes were identified, of which 28 proteins exhibited hydrolase activity. Among the 28 proteins, we focused on two enzymes (M9QMC9 and B7VF65). Based on proteomics, a cysteine protease (M9QMC9) with a molecular weight of 25.8 kDa and milk-clotting activity was purified from D. sinensis stems using double ammonium sulfate precipitation and was confirmed using liquid chromatography-mass spectrometry (LC-MS/MS). The milk-clotting temperature using the purified enzyme was around 80 °C (specific activity at 314.38 U/mg), and it was found to be stable in the pH range of 6-9 in NaCl concentration of <0.8 mol/L. These findings indicated that the enzyme isolated from D. sinensis stems has potential in the dairy and food sectors, especially in the cheese-making industry.

Novel Bacillus Milk-Clotting Enzyme Produces Diverse Functional Peptides in Semihard Cheese

Although rennet is one of the best choices for cheese manufacturing, its production cannot meet the growing demands of the cheese industry. Thus, new milk-clotting enzymes (MCEs) with similar or better properties as/than those of calf chymosin are needed urgently. Here, three MCEs, BY-2, BY-3, and BY-4, were mined by bioinformatic analysis and then expressed in and isolated from Escherichia coli. BY-4 had the highest milk-clotting activity/proteolytic activity (238.76) with enzyme properties similar to those of calf chymosin. BY-4 cheese had a composition, appearance, consistency/texture, and overall acceptability proximate to calf chymosin cheese. The EC₅₀ values of peptides extracted from BY-4 cheese for 2,2-diphenyl-1-picrylhydrazyl inhibition (antioxidant property), angiotensin-converting enzyme inhibition (antihypertensivity), and growth inhibition of liver cancer cells (antitumor property) were found to be 81, 49, and 238 μg/mL, respectively, which were 2.35, 2.59, and 2.12 folds higher than those of calf chymosin cheese. These results indicated the potential of BY-4 as a supplement to calf chymosin in cheese manufacturing, especially for functional and health care purposes.

Toward alternative sources of milk coagulants for cheese manufacturing: establishment of hairy roots culture and protease characterization from Cynara cardunculus L

Extracts from hairy root cultures of Cynara cardunculus L. contain proteases and show milk-clotting activity. Cynara cardunculus L. or cardoon is often used as rennet in traditional cheese manufacturing, due to the presence of specific proteases in the flower. However, the flower extracts are variable depending on the provenance and quality of the flowers as well as high genetic variability among cardoon populations, and this affects the quality of the final product. In search for alternative sources of milk-clotting enzymes, hairy root cultures from cardoon were obtained and characterized regarding their protease content and proteolytic activity toward milk proteins. Aspartic, serine and cysteine proteases were identified in hairy roots by mass spectrometry analysis and an azocasein assay combined with specific inhibitors. RT-PCR analysis revealed the expression of cardosin A and D, and immunoblotting analysis suggested the presence of cardosin A or cardosin A-like enzyme in its mature form, supporting this system as an alternative source of cardosins. Hairy root protein extracts showed activity over caseins, supporting its use as milk coagulant, which was further tested by milk-clotting assays. This is also the first report on the establishment of hairy root cultures from cardoon, which paves the way for future work on controlled platforms for production of valuable metabolites which are known to be present in this species.

Proteases from Calotropis gigantea stem, leaf and calli as milk coagulant source

Background:

Universal demand for cheese keeps the search for appropriate enzymes from plants mimicking animal rennet action in scientific focus.

Objective:

To associate distribution of milk clotting potential and profile of whole/κ-casein hydrolysis by Calotropis gigantea stem, leaf and respective calli crude enzymes (CE).

Materials and methods:

Milk clotting activity and index were assayed for CE. Caseinolytic activity (CA) was evaluated spectrophotometrically. 0.5 CA units of CE and Enzeco® were used for studying whole/κ-casein hydrolysis pattern by Tricine SDS-PAGE. Inhibition studies were performed for enzyme characterisation.

Results:

Traditionally propagated (TP) stem and its callus CE exhibited high specific milk clotting activity (1297.30±0.2 U/mg of protein and 926.74±44.13 U/mg of protein, respectively) and milk clotting index (103.562±1.162 and 79.365±4.93, respectively). Comparison of whole casein hydrolytic pattern by 0.5 CA units of CE revealed closer resemblance between leaf callus and Enzeco®. However, κ-casein specificity analysis revealed TP leaf to be closely mimicking the performance by Enzeco®.

Conclusion:

Study suggests CE from TP leaf to be a potential vegetable coagulant to work as an effective and low-cost milk clotting mediator in cheese industry.

Improving the catalytic, kinetic and thermodynamic properties of Bacillus subtilis KU710517 milk clotting enzyme via conjugation with polyethylene glycol

Milk clotting enzyme (MCE) produced by Bacillus subtilis KU710517 was conjugated to several activated polysaccharides. Among all the conjugates, the enzyme conjugated with polyethylene glycol (PEG) exhibited the highest retained activity (551U/mg protein) with a recovered activity of 95.3%. The activation energy of PEG-conjugated enzyme was calculated as 24.56kJ·mol^-1which was lower than that of the native one (29.27kJ·mol^-1) however, the temperature quotient (Q₁₀) was about 1.08 for the two forms of the enzyme. The calculated half-life times of PEG-conjugated enzyme at 55 and 60°C were 317.78 and 128.6min respectively, whereas at the same temperatures the native enzyme had lower half-life times (53 and 19.6min respectively). The data of thermodynamic analysis for substrate catalysis including the specificity constant (V_max/K_m), turnover number (k_cat), catalytic efficiency (k_cat/K_m), enthalpy of activation (ΔH*), free energy of activation (ΔG*), free energy for transition state formation ΔG*_E-T and free energy of substrate binding ΔG*_E-S were determined for both native and PEG-conjugated enzyme. In addition, the thermodynamic parameters for irreversible inactivation (ΔH, ΔG, ΔS) were evaluated. The calculated results indicated that the catalytic properties after the PEG-conjugation were significantly improved.

Rheological and structural properties of enzyme-induced gelation of milk proteins by ficin and Polyporus badius

The rheological and microstructural characteristics of ewes’ milk curd obtained by coagulating with milk‐clotting enzymes, including ficin extract and Polyporus badius were evaluated. The gelation of milk was examined by small amplitude oscillatory shear measurements (SAOS). Different concentrations of ficin and P. badius extracts (1, 3, and 5%) were utilized to coagulate milk proteins. The ewes’ samples containing ficin and mushroom enzymes were heated from 25 to 45°C at a heating rate 1°C/min and kept for 30 min. Then, the curds were cooled down to 25°C with the same heating rate. The ficin extract could induce stronger gels at 45°C and 5% ficin. Similar results were also found for 5% P. badius extract and incubation at 45°C. However, P.badius gels achieved a network with more viscous characteristics and had a softer texture than ficin gels. Therefore, it may be concluded the induced gels with mushroom had higher moisture and lower protein contents, which related to the high proteolytic activity of P. badius. The microstructure survey showed that the mushroom‐induced gel had a more compact structure. By increasing enzyme concentration, both gels showed a coarser and more compact protein network. Whereas, the P. badius gels had more fusions and folds which indicate the greater proteolysis occurred during gelation and there was greater breakdown of protein. Our findings suggest the application of ficin and P. badius enzymes to develop a novel procedure to coagulate milk proteins and providing new structures in food systems.

Utility of Milk Coagulant Enzyme of Moringa oleifera Seed in Cheese Production from Soy and Skim Milks

In this study, the potential use of Moringa oleifera as a clotting agent of different types of milk (whole, skim, and soy milk) was investigated. M. oleifera seed extract showed high milk-clotting activity followed by flower extract. Specific clotting activity of seed extract was 200 times higher than that of flower extract. Seed extract is composed by four main protein bands (43.6, 32.2, 19.4, and 16.3 kDa). Caseinolytic activity assessed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and tyrosine quantification, showed a high extent of casein degradation using M. oleifera seed extract. Milk soy cheese was soft and creamy, while skim milk cheese was hard and crumbly. According to these results, it is concluded that seed extract of M. oleifera generates suitable milk clotting activity for cheesemaking. To our knowledge, this study is the first to report comparative data of M. oleifera milk clotting activity between different types of soy milk.

Effect of extraction pH on techno-functional properties of crude extracts from wild cardoon (Cynara cardunculus L.) flowers

In the present paper, techno-functional properties of rennet derived from C. cardunculus, prepared at various pH (from 3 to 6), were investigated. It was found that the extract prepared at pH 3 had the best milk-clotting properties (MCA/PA ratio). It presented also the highest enzyme content, determined by densitometry analysis on 1D and 2D gels electrophoresis. Formation of milk gels produced by the extracts and chymosin was monitored using dynamic rheology and turbiscan. It can be assumed that by lowering rennet pH, milk pH decreases, causing a significant increase of curd firmness and both elastic (G') and viscous (G″) moduli. Results obtained by turbiscan showed similar ΔBS values of gels produced, after 2h, by chymosin and the crude extract at pH 3. In conclusion, C. cardunculus extract prepared at low pH has the potential to be employed as an efficient milk-clotting agent in the production of dairy products.

Partial Characterization of the Proteolytic Properties of an Enzymatic Extract From "Aguama" Bromelia pinguin L. Fruit Grown in Mexico

Plant proteases are capable of performing several functions in biological systems, and their use is attractive for biotechnological process due to their interesting catalytic properties. Bromelia pinguin (aguama) is a wild abundant natural resource in several regions of Central America and the Caribbean Islands but is underutilized. Their fruits are rich in proteases with properties that are still unknown, but they represent an attractive source of enzymes for biotechnological applications. Thus, the proteolytic activity in enzymatic crude extracts (CEs) from wild B. pinguin fruits was partially characterized. Enzymes in CEs showed high proteolytic activity at acid (pH 2.0-4.0) and neutral alkaline (pH 7.0-9.0) conditions, indicating that different types of active proteases are present. Proteolytic activity inhibition by the use of specific protease inhibitors indicated that aspartic, cysteine, and serine proteases are the main types of proteases present in CEs. Activity at pH 3.0 was stable in a broad range of temperatures (25-50 °C) and retained its activity in the presence of surfactants (SDS, Tween-80), reducing agents (DTT, 2-mercapoethanol), and organic solvents (methanol, ethanol, acetone, 2-propanol), which suggests that B. pinguin proteases are potential candidates for their application in brewing, detergent, and pharmaceutical industries.

Three phase partitioning of zingibain, a milk-clotting enzyme from Zingiber officinale Roscoe rhizomes

The present work describes for the first time an elegant non-chromatographic method, the three phase partitioning for the purification and recovery of zingibain, a milk-clotting enzyme, from Zingiber officinale rhizomes. Factors affecting partitioning efficiency such as (NH4)2SO4 saturation, crude extract to t-butanol ratio and pH on zingibain partitioning were investigated. Optimal purification parameters were 50% (NH4)2SO4 saturation with 1.0:1.0 ratio of crude extract:t-butanol at pH 7.0, which gave 14.91 purification fold with 215% recovery of zingibain. The enzyme was found to be exclusively partitioned in the aqueous phase. The enzyme showed a prominent single band on SDS-PAGE. It is a monomeric protein of 33.8 kDa and its isoelectric point is 4.38. The enzyme exhibited maximal proteolytic activity at a temperature of 60 °C and pH 7.0. It was found to be stable at 40-65 °C during 2 h. The enzyme was found to be highly stable against numerous metal ions and its activity was enhanced by Ca(2+), K(+) and Na(+). It was completely inhibited by heavy metal ions such as Cu(2+) and Hg(2+) and partially by Cd(+). Zingibain milk-clotting activity (MCA) was found to be highly stable when stored under freezing (-20 °C) for 30 days compared at 4 °C.

Purification and characterisation of κ-casein specific milk-clotting metalloprotease from Termitomyces clypeatus MTCC 5091

Milk-clotting enzymes are valued as chymosin-like protease substitutes for cheese making industries. An extracellular metalloprotease (AcPs) with high milk-clotting activity was purified from edible mushroom Termitomyces clypeatus and characterised. AcPs was preferentially active towards κ-casein, analysed by Urea-PAGE and LC-ESI-MS, whereas the degradation of α and β-casein components by AcPs proceeded slowly justifying its suitability for cheese making. RP-HPLC peptide profiling revealed that the AcPs activity on milk casein was similar to that of a commercial milk coagulant. The enzyme exhibited pH and temperature optima at 5.0 and 45 °C, respectively and showed a pI value of 4.6. One- and two dimensional zymographies revealed a single polypeptide band with proteolytic signal. The MALDI-TOF/MS followed by peptide mass fingerprinting revealed homology with a predicted protein of Populus trichocarpa. To our knowledge, this is the first report on a metalloprotease from T. clypeatus, and the results indicate that this enzyme can be considered as a potential substitute for chymosin in cheese manufacturing.

Milk-Coagulating Extract Produced from Solanum aethiopicum Shum Fruits: Multivariate Techniques of Preparation, Thermal Stability and Effect on Milk Solids Recovery in Curd

This study investigated a novel procedure of Solanum aethiopicum Shum fruits extract (SASFE) preparation using multivariate experimental designs as factorial and Box–Behnken. The thermal stability of optimized extract as well as its influence on the milk solids in curd was determined. The results showed that extraction time, fruit maturity and pH did not affect significantly SASFE preparation, while the amount of fruits, extraction temperature and NaCl concentration of extractant had a significant effect (p < 0.05). The greatest coagulant index was obtained under the following conditions: 12.5% of fruits, 25°C of extraction temperature and 4% NaCl concentration of extractant. It was thermosensitive and exhibited optimum temperature at 50°C. There was no statistical difference between SASFE and calf rennet in terms of solids yield in curd, estimated yield and actual yield. On the basis of these results, SASFE can be used as a vegetable alternative to calf rennet.

Cloning, expression, and characterization of a milk-clotting aspartic protease gene (Po-Asp) from Pleurotus ostreatus

An aspartic protease gene from Pleurotus ostreatus (Po-Asp) had been cloned based on the 3' portion of cDNA in our previous work. The Po-Asp cDNA contained 1,324 nucleotides with an open reading frame (ORF) of 1,212 bp encoding 403 amino acid residues. The putative amino acid sequence included a signal peptide, an activation peptide, two most possible N-glycosylation sites and two conserved catalytic active site. The mature polypeptide with 327 amino acid residues had a calculated molecular mass of 35.3 kDa and a theoretical isoelectric point of 4.57. Basic Local Alignment Search Tool analysis showed 68-80 % amino acid sequence identical to other basidiomycetous aspartic proteases. Sequence comparison and evolutionary analysis revealed that Po-Asp is a member of fungal aspartic protease family. The DNA sequence of Po-Asp is 1,525 bp in length without untranslated region, consisting of seven exons and six introns. The Po-Asp cDNA without signal sequence was expressed in Pichia pastoris and sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated the molecular mass of recombinant Po-Asp was about 43 kDa. The crude recombinant aspartic protease had milk-clotting activity.

Properties and applications of phytepsins from thistle flowers

Aqueous extracts of thistle flowers from the genus Cynara-Cardueae tribe Cass. (Cynareae Less.), Asteraceae Dumortier-are traditionally used in the Mediterranean region for production of artisanal cheeses. This is because of the presence of aspartic proteases (APs) with the ability to coagulate milk. Plant APs, collectively known as phytepsins (EC 3.4.23.40), are bilobed endopeptidases present in an ample variety of plant species with activity mainly at acidic pHs, and have two aspartic residues located on each side of a catalytic cleft that are responsible for catalysis. The cleavage of the scissile peptide-bond occurs primarily between residues with large hydrophobic side-chains. Even when aspartylendopeptidase activity in plants is normally present at relatively low levels overall, the flowers of several species of the Cardueae tribe possess APs with extremely high specific activities in certain tissues. For this reason, in the last two decades, APs present in thistle flowers have been the subject of intensive study. Present here is a compilation of work that summarizes the known chemical and biological properties of these proteases, as well as their biomedical and biotechnological applications.

Production of plant proteases in vivo and in vitro--a review

In the latest two decades, the interest received by plant proteases has increased significantly. Plant enzymes such as proteases are widely used in medicine and the food industry. Some proteases, like papain, bromelain and ficin are used in various processes such as brewing, meat softening, milk-clotting, cancer treatment, digestion and viral disorders. These enzymes can be obtained from their natural source or through in vitro cultures, in order to ensure a continuous source of plant enzymes. The focus of this review will be the production of plant proteases both in vivo and in vitro, with particular emphasis on the different types of commercially important plant proteases that have been isolated and characterized from naturally grown plants. In vitro approaches for the production of these proteases is also explored, focusing on the techniques that do not involve genetic transformation of the plants and the attempts that have been made in order to enhance the yield of the desired proteases.