A novel milk-clotting cysteine protease from Ficus johannis: Purification and characterization

Isolation and identification of milk-clotting proteases from Prinsepia utilis Royle and its application in cheese processing

The aim of this study was to isolate and identify the main milk-clotting proteases from Prinsepia utilis Royle. Protein isolates obtained using precipitation with 20 %-50 % ammonium sulfate (AS) showed higher milk-clotting activity (MCA) at 154.34 + 0.35 SU. Two milk-clotting proteases, namely P191 and P1831, with molecular weight of 49.665 kDa and 68.737 kDa, respectively, were isolated and identified using liquid chromatography-mass spectrometry (LC-MS/MS). Bioinformatic analysis showed that the two identified milk-clotting proteases were primarily involved in hydrolase activity and catabolic processes. Moreover, secondary structure analysis showed that P191 structurally consisted of 40.85 % of alpha-helices, 15.96 % of beta-strands, and 43.19 % of coiled coil motifs, whereas P1831 consisted of 70 % of alpha-helices, 7.5 % of beta-strands, and 22.5 % of coiled coil motifs. P191 and P1831 were shown to belong to the aspartic protease and metalloproteinase types, and exhibited stability within the pH range of 4-6 and good thermal stability at 30-80 °C. The addition of CaCl2 (<200 mg/L) increased the MCA of P191 and P1831, while the addition of NaCl (>3 mg/mL) inhibited their MCA. Moreover, P191 and P1831 preferably hydrolyzed kappa-casein, followed by alpha-casein, and to a lesser extent beta-casein. Additionally, cheese processed with the simultaneous use of the two proteases isolated in the present study exhibited good sensory properties, higher protein content, and denser microstructure compared with cheese processed using papaya rennet or calf rennet. These findings unveil the characteristics of two proteases isolated from P. utilis, their milk-clotting properties, and potential application in the cheese-making industry.

Role of Clay Substrate Molecular Interactions in Some Dairy Technology Applications

The use of clay materials in dairy technology requires a multidisciplinary approach that allows correlating clay efficiency in the targeted application to its interactions with milk components. For profitability reasons, natural clays and clay minerals can be used as low-cost and harmless food-compatible materials for improving key processes such as fermentation and coagulation. Under chemical stability conditions, clay materials can act as adsorbents, since anionic clay minerals such as hydrotalcite already showed effectiveness in the continuous removal of lactic acid via in situ anion exchange during fermentation and ex situ regeneration by ozone. Raw and modified bentonites and smectites have also been used as adsorbents in aflatoxin retention and as acidic species in milk acidification and coagulation. Aflatoxins and organophilic milk components, particularly non-charged caseins around their isoelectric points, are expected to display high affinity towards high silica regions on the clay surface. Here, clay interactions with milk components are key factors that govern adsorption and surface physicochemical processes. Knowledge about these interactions and changes in clay behavior according to the pH and chemical composition of the liquid media and, more importantly, clay chemical stability is an essential requirement for understanding process improvements in dairy technology, both upstream and downstream of milk production. The present paper provides a comprehensive review with deep analysis and synthesis of the main findings of studies in this area. This may be greatly useful for mastering milk processing efficiency and envisaging new prospects in dairy technology.

Optimization of caseinolytic and coagulating activities of Solanum tuberosum rennets for cheese making

BACKGROUND

In recent years, the rising global demand for cheese, the high cost and limited supply of calf rennet, and consumer choices have increased research into new alternatives to animal or recombinant chymosins for cheese making. Plant proteases with caseinolytic activity (CA) and milk-clotting activity (MCA) have been proposed as alternatives for milk clotting to obtain artisanal cheeses with new organoleptic properties. They have been named vegetable rennets (vrennets). The aim of this study was to evaluate the performance of two Solanum tuberosum aspartic proteases (StAP1 and StAP3) as vrennets for cheese making and to obtain a statistical model that could predict and optimize their enzymatic activity.

RESULTS

To optimize the CA and MCA activities, a response surface methodology was used. Maximum values of CA and MCA for both enzymes were found at pH 5.0 and 30-35 °C. Analysis of the degradation of casein subunits showed that it is possible to tune the specificity of both enzymes by changing the pH. At pH 6.5, the αS - and β- subunit degradation is reduced while conserving a significant MCA.

CONCLUSION

The statistical models obtained in this work showed that StAP1 and StAP3 exert CA and MCA under pH and temperature conditions compatible with those used for cheese making. The casein subunit degradation percentages obtained also allowed us to select the best conditions for the degradation of the κ-casein subunit by StAPs. These results suggest that StAP1 and StAP3 are good candidates as vrennets for artisan cheese making. © 2023 Society of Chemical Industry.

Plant-derived rennet: research progress, novel strategies for their isolation, identification, mechanism, bioactive peptide generation, and application in cheese manufacturing

Rennet, an aspartate protease found in the stomach of unweaned calves, effectively cuts the peptide bond between Phe105-Met106 in κ-casein, hydrolyzing the casein micelles to coagulate the milk and is a crucial additive in cheese production. Rennet is one of the most used enzymes of animal origin in cheese making. However, using rennet al.one is insufficient to meet the increasing demand for cheese production worldwide. Numerous studies have shown that plant rennet can be an alternative to bovine rennet and exhibit a good renneting effect. Therefore, it is crucial and urgent to find a reliable plant rennet. Based on our team's research on rennet enzymes of plant origin, such as from Dregea sinensis Hemsl. and Moringa oleifer Lam., for more than ten years, this paper reviews the relevant literature on rennet sources, isolation, identification, rennet mechanism, functional active peptide screening, and application in cheese production. In addition, it proposes the various techniques for targeted isolation and identification of rennet and efficient screening of functionally active peptides, which show excellent prospects for development.

Characteristics and application in cheese making of newly isolated milk-clotting enzyme from Bacillus megaterium LY114

Milk-clotting enzyme (MCE) is a crucial active agent in cheese making. It is necessary to find traditional MCE substitutes due to the limited production of traditional MCE (e.g., calf rennet) and increased cheese consumption. Bacillus megaterium strain LY114 with good milk-clotting activity (MCA) (448 SU/mL) and a high MCA/proteolytic activity (PA) ratio (6.0) was isolated and identified from agricultural soil in Laiyang (Shandong, China) through 16S rRNA sequencing of 45 strains. The Bacillus megaterium LY114 MCE had a remarkable specific activity (7532 SU/mg) and displayed a 4.83-fold purification yield with 34.17% recovery through ammonium sulfate fractionation and DEAE-Sepharose Fast Flow. The purified LY114 MCE was a metalloprotease with a molecular weight of 30 kDa. LY114 MCE was stable at pH 5.0-7.0 and temperature <40 °C. The highest MCA appeared at a substrate pH of 5.5 with 30 mM CaCl2. The Michaelis constant (Km) and maximal velocity (Vm) for casein were 0.31 g/L and 14.16 μmol/min, respectively. LY114 MCE preferred to hydrolyze α-casein (α-CN) rather than β-casein (β-CN) and had unique α-CN, β-CN and κ-casein (κ-CN) cleavage sites. LY114 MCE hydrolyzed casein to generate significantly different peptides compared with calf rennet and fungal MCE as determined by SDS-PAGE analysis. Chemical index analysis and sensory evaluation confirmed the usefulness of LY114 MCE in cheese making. LY114 MCE had the potential to be used in dairy processing and enriched traditional MCE substitutes.

Analysis of the effect of Tenebrio Molitor rennet on the flavor formation of Cheddar cheese during ripening based on gas chromatography-ion mobility spectrometry (GC-IMS)

This study aimed to evaluate the potential application of Tenebrio Molitor rennet (TMR) in Cheddar cheese production, and to use gas chromatography-ion mobility spectrometry (GC-IMS) to monitor flavor compounds and fingerprints of cheese during ripening. The results indicated that Cheddar cheese prepared from TMR (T_F) has fat content significantly lower than that of commercial rennet (C_F) (p < 0.05). However, the results of the sensory evaluation showed that there were no statistically significant differences between the two kinds of cheese (p > 0.05). Both cheeses were rich in free amino acids and free fatty acids. Compared to the C_F cheese, gamma-aminobutyric acid and Ornithine contents of the T_F cheese reached 187 and 749 mg/kg, respectively, during 120 days of ripening. Moreover, GC-IMS provided information on the characteristics of 40 flavor substances (monomers and dimers) in the T_F cheese during ripening. Only 30 flavor substances were identified in the C_F cheese. The fingerprint of the two kinds of cheese during ripening can be established by GC-IMS and principal component analysis based on the identified flavor compounds. Therefore, TMR has potential application in Cheddar cheese production. GC-IMS might be applied for the quick, accurate and comprehensive monitoring of cheese flavor during ripening.

Plant extracts and essential oils in the dairy industry: A review

Plants have been used as food additives worldwide to enhance the sensory qualities of foods and extend their shelf life by reducing or eliminating foodborne pathogens. They also serve as therapeutic agents due to their beneficial effects on human health through their anti-cancerous, anti-inflammatory, antioxidant, and immune-modulatory properties. Plants can be added to food as a dry powder, grated material, paste, juice, or as an extract that can be produced by a variety of methods. Plant extracts and essential oils are concentrated sources of bioactive phytochemicals that can be added to food in small amounts in a variety of forms. These forms include liquid, semi-solid, or dry powder for easy and uniform diffusion. Encapsulation can protect bioactive compounds from temperature, moisture, oxidation, and light, as well as allow for controlling the release of the encapsulated ingredients. Nanoemulsions can enhance the bioactivity of active components. This review explains how plant extracts and essential oils are used in the dairy industry as antimicrobial materials, analyzing their impact on starter bacteria; as natural antioxidants to prevent the development of off-flavors and increase shelf life; and as technological auxiliaries, like milk-clotting enzymes, stabilizers, and flavoring agents. Therefore, plant extracts and essential oils are a better choice for the dairy industry than plants or their parts due to a wide range of applications, homogeneous dispersion, and ability to control the concentration of the bioactive ingredients and enhance their efficiency.

The catalytic and kinetic characterization of Bacillus subtilis MK775302 milk clotting enzyme: comparison with calf rennet as a coagulant in white soft cheese manufacture

BACKGROUND

Calf rennet is considered the traditional source of milk clotting enzyme (MCE). However, increasing cheese consumption with decreasing the calf rennet supply had encouraged the quest for new rennet alternatives. The purpose of this study is to acquire more information about the catalytic and kinetic properties of partially purified Bacillus subtilis MK775302 MCE and to assess the role of enzyme in cheese manufacture.

RESULTS

B. subtilis MK775302 MCE was partially purified by 50% acetone precipitation with 5.6-fold purification. The optimum temperature and pH of the partially purified MCE were 70 °C and 5.0, respectively. The activation energy was calculated as 47.7 kJ/mol. The calculated Km and Vmax values were 36 mg/ml and 833 U/ml, respectively. The enzyme retained full activity at NaCl concentration of 2%. Compared to the commercial calf rennet, the ultra-filtrated white soft cheese produced from the partially purified B. subtilis MK775302 MCE exhibited higher total acidity, higher volatile fatty acids, and improved sensorial properties.

CONCLUSIONS

The partially purified MCE obtained in this study is a promising milk coagulant that can replace calf rennet at a commercial scale to produce better-quality cheese with improved texture and flavor.

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.

Purification of Extracellular Protease from Staphylococcus simulans QB7and Its Ability in Generating Antioxidant and Anti-inflammatory Peptides from Meat Proteins

Proteases, especially microbial proteases, are widely used in food processing. The purpose of this study was aimed to purify an extracellular protease produced by the strain Staphylococcus simulans QB7 and to evaluate its ability in hydrolyzing meat proteins and generating antioxidant and anti-inflammatory peptides. The optimal conditions for producing the enzyme were as follows: inoculum ratio, 10%; initial pH, 6.5; temperature, 32 °C; incubation time, 36 h; and rotation speed, 160 rpm. The protease had a molecular weight of approximately 47 kDa, possessing the optimal activity at 50 °C, pH 7.0, The protease was stable at pH 4.0-8.0 and 30-60 °C, and the activity was improved by Na⁺, Mg²⁺, Ca²⁺, and Zn²⁺ ions, whereas it was inhibited by Cu²⁺, Co²⁺, Fe³⁺, Ba²⁺, Fe²⁺, β-M, and ethylene diamine tetraacetic acid disodium salt (EDTA). The protease could effectively hydrolyze meat proteins, and the generated hydrolysate could significantly inhibit tumor necrosis factor-alpha (TNFα)-induced oxidative stress, including superoxide and malondialdehyde levels and inflammation (vascular adhesion molecule-1 [VCAM-1] and cyclooxygenase 2 [COX2)) in human vascular EA.hy926 cells. The present findings support the ability of S. simulans QB7 protease in generating antioxidant and anti-inflammatory peptides during the fermentation of meat products.

Milk-Gelling Properties of Proteases Extracted from the Fruits of Solanum Elaeagnifolium Cavanilles

There is little information on the milk coagulation process by plant proteases combined with chymosins. This work is aimed at studying the capability of protease enclosed in the ripe fruits of Solanum elaeagnifolium (commonly named trompillo) to form milk gels by itself and in combination with chymosin. For this purpose, proteases were partially purified from trompillo fruits. These proteases had a molecular weight of ~60 kDa, and results suggest cucumisin-like serine proteases, though further studies are needed to confirm this observation. Unlike chymosins, trompillo proteases had high proteolytic activity (PA = 50.23 U_Tyr mg protein⁻¹) and low milk-clotting activity (MCA = 3658.86 SU mL⁻¹). Consequently, the ratio of MCA/PA was lower in trompillo proteases (6.83) than in chymosins (187 to 223). Our result also showed that milk gels formed with trompillo proteases were softer (7.03 mPa s) and had a higher release of whey (31.08%) than the milk gels clotted with chymosin (~10 mPa s and ~4% of syneresis). However, the combination of trompillo proteases with chymosin sped up the gelling process (21 min), improved the firmness of milk gels (12 mPa s), and decreased the whey release from milk curds (3.41%). Therefore, trompillo proteases could be combined with chymosin to improve the cheese yield and change certain cheese features.

Purification and Characterization of the Protease from Staphylococcus xylosus A2 Isolated from Harbin Dry Sausages

The protease generated from Staphylococcus (S.) xylosus A2, which was isolated from Harbin dry sausages, was purified and characterized. The molecular weight of the purified protease was approximately 21.5 kDa, and its relative activity reached the highest at pH 6.0 and 50 °C. At pH 4.0−8.0 and temperatures of 20−50 °C, the protease was stable. Its activity was significantly improved by Ca2+ and Zn2+ ions (p < 0.05). The Michaelis constant and maximum velocity of the protease were 2.94 mg/mL and 19.45 U/mL·min, respectively. The thermodynamic parameters analysis suggested that the protease showed better catalytic properties at 40 °C. Moreover, the protease could hydrolyze meat proteins, and obtained hydrolysate is non-cytotoxic to the HEK-293 cells. These findings provide a theoretical basis for understanding the enzymatic characterization of S. xylosus A2 protease and its future application in fermented meat products.

Development of energy-rich protein bars and in vitro determination of angiotensin I-converting enzyme inhibitory antihypertensive activities

Three energy-rich protein (ERP) bars were prepared to meet the daily recommended dietary allowance (RDA) for the protein of Pakistani athletes. The bars were developed using dates, cheddar cheese (CC), whey protein isolate (WPI), roasted chickpea flour, and rice flour in different proportions. Bar #1 contained 64 g dates, 16 g dried apricots, 12 g WPI, and 8 g ripened CC. Bar #2 contained the same proportion of these ingredients with an addition of 12.5 g roasted chickpea flour, while bar #3 contained 6.25 g roasted rice and 6.25 g roasted chickpea flour. All the ingredients were homogeneously mixed into paste to form bars weighing 100-110 g per serving size. These bars were studied for the compositional analysis (moisture, protein, and lipid content), protein characterization through sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and in vitro determination of the angiotensin I-converting enzyme (ACE-I) antihypertensive activity. Moisture and lipid content in bars were 22% and 0.057%-0.313%, respectively, while protein, fiber, and ash contents varied from 22.3% to 23.6%, 6.66 to 5.81, and 2.12% to 2.44%, respectively. The minimum energy content was recorded (272.70 Kcal/100 g) in bar #1 while bar #3 showed the highest energy content 274.65 Kcal/110 g with the addition of (5%) roasted chickpea and rice flour, respectively. Electrophoresis analysis of proteins in bar # 1 (cheese +WPI) showed the four bands at 62, 24, 20, and 12 kDa. Bar #2 (10% roasted chickpea flour) showed some additional bands at 40, 36, 34, and 28 kDa while relatively lower antihypertensive activity than bars #1 and 3. The study revealed that adding 10% roasted chickpea flour (bar #2) increased the protein content and diversity in proteins. It provided 40% proteins to athletes and could be helpful to meet their R.D.A. by consuming two bars/day.

Plant Milk-Clotting Enzymes for Cheesemaking

The reduced availability and the increasing prices of calf rennet, coupled to the growing global demand of cheese has led, worldwide, to explore alternative clotting enzymes, capable to replace traditional rennet, during the cheesemaking. In addition, religious factors and others related to the vegetarianism of some consumers, have led to alternative rennet substitutes. Nowadays, several plant-derived milk-clotting enzymes are available for cheesemaking technology. Many efforts have also been made to compare their effects on rheological and sensory properties of cheese to those arising from animal rennet. However, vegetable clotting enzymes are still partially suitable for cheesemaking, due to excessive proteolytic activity, which contribute to bitter flavor development. This review provides a literature overview of the most used vegetable clotting enzymes in cheese technology, classified according to their protease class. Finally, clotting and proteolytic activities are discussed in relation to their application on the different cheesemaking products.

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.

Thermostable trypsin-like protease by Penicillium roqueforti secreted in cocoa shell fermentation: Production optimization, characterization, and application in milk clotting

The increased demand for cheese and the limited availability of calf rennet justifies the search for milk-clotting enzymes from alternative sources. Trypsin-like protease by Penicillium roqueforti was produced by solid-state fermentation using cocoa shell waste as substrate. The production of a crude enzyme extract that is rich in this enzyme was optimized using a Doehlert-type multivariate experimental design. The biochemical characterization showed that the enzyme has excellent activity and stability at alkaline pH (10-12) and an optimum temperature of 80°C, being stable at temperatures above 60°C. Enzymatic activity was maximized in the presence of Na⁺ (192%), Co²⁺ (187%), methanol (153%), ethanol (141%), and hexane (128%). Considering the biochemical characteristics obtained and the milk coagulation activity, trypsin-like protease can be applied in the food industry, such as in milk clotting and in the fabrication of cheeses.

Advances in research on calf rennet substitutes and their effects on cheese quality

Milk coagulation is an important step in cheese production, and milk-clotting enzymes (MCEs) play a major role in this process. Calf rennet is the most widely used MCE in the cheese industry. The use of calf rennet substitutes is becoming necessary due to the limited availability of calf rennet and the increase in cheese consumption. The objective of this review is to summarize the latest findings on calf rennet substitutes (animal MCEs, plant-derived MCEs, recombinant MCEs and microbial MCEs) and their application in cheese production. Special emphasis has been placed on aspects of the effects of these substitutes on hydrolysis, functional peptides, cheese variety and cheese yield. The advantages and disadvantages of different calf rennet substitutes are discussed, in which microbial MCEs have the advantages of less expensive production, greater biochemical diversity, easier genetic modification, etc. In particular, some of these MCEs have suitable characteristics for cheese production and are considered to be the most potential calf rennet substitutes. Moreover, challenges and future perspectives are presented to provide inspiration for the development of excellent calf rennet substitutes.

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.

Constitutive expression of Camelus bactrianus prochymosin B in Pichia pastoris

Camel chymosin can be efficiently employed to produce cheese. Traditionally the rennet enzyme produced by the glands of the fourth stomach of ruminant animals (abomassum) is used in cheese making. Full-length Camelus bactrianus (Bactrian camel) prochymosin gene was synthesized and constitutively expressed in Pichia pastoris cells under glyceraldehydes-3-phosphate dehydrogenase (GAP) promoter. It was purified by sequential anion and cation exchange chromatography. SDS-PAGE analysis resulted in two bands, approximately 42 and 35 kDa. The 42 kDa band vanished when the sample was treated with endoglycosidase H, indicating that the recombinant protein is partially glycosylated. Optimal pH for the activity of the highest-purity recombinant chymosin was pH 4.5 for cow's milk and pH 4.0 for mare's milk. The range 45–50 °C and 70 °C for cow's and mare's milk types, respectively, was found to be the most appropriate for maximal relative milk-clotting activity. Concentration of CaCl₂ that ensured the stability of the chymosin milk-clotting activity was between 20 and 50 mM with an optimum at 30 mM. Milk-clotting activity of camel recombinant chymosin and ability to make curd was successfully tested on fresh mare's milk. Pichia pastoris strain with integrated camel chymosin gene showed high productivity of submerged fermentation in bioreactor with milk-clotting activity 1412 U/mL and 80 mg/L enzyme yield. These results suggest that the constitutive expression of the camel chymosin Camelus bactrianus in the yeast Pichia pastoris has good prospects for practical applications.

Biochemical properties of extracellular protease from Staphylococcus carnosus RT6 isolated from Harbin dry sausages, and its hydrolysis of meat proteins

The characteristics of the extracellular protease, produced by Staphylococcus carnosus RT6 isolated from Harbin dry sausages, and its hydrolysis of meat proteins were investigated. The protease was purified by ammonium sulfate, ion exchange, and gel filtration chromatography to obtain a 20.0 kDa extracellular protease. The protease reached maximal activity at pH 9.0 and 50 °C and was stable at pH 7.0 to 11.0 and 20 to 40 °C. Its protease activity was easily inhibited in the presence of Zn²⁺ , Fe²⁺ , and Fe³⁺ . The enzymatic characterization of the protease revealed a V_max 49.50 U/ml·min, K_m 8.19 mg/ml, and the half-life = 28.06 min, ΔH^* _d  = 114.11 kJ/mol, ΔG^* _d  = 89.24 kJ/mol, and ΔS^* _d  = 77.00 J/mol·K at 50 °C. In addition, the protease hydrolyzed meat protein into small particles and produced soluble peptides. This study provides a basis for understanding the biochemical characteristics of the S. carnosus RT6 protease and its future application for fermented meat products.

Cohnella 1759 cysteine protease shows significant long term half-life and impressive increased activity in presence of some chemical reagents

Thermostability and substrate specificity of proteases are major factors in their industrial applications. rEla is a novel recombinant cysteine protease obtained from a thermophilic bacterium, Cohnella sp.A01 (PTCC No: 1921). Herein, we were interested in recombinant production and characterization of the enzyme and finding the novel features in comparison with other well-studied cysteine proteases. The bioinformatics analysis showed that rEla is allosteric cysteine protease from DJ-1/ThiJ/PfpI superfamily. The enzyme was heterologously expressed and characterized and the recombinant enzyme molecular mass was 19.38 kD which seems to be smaller than most of the cysteine proteases. rEla exhibited acceptable activity in broad pH and temperature ranges. The optimum activity was observed at 50℃ and pH 8 and the enzyme showed remarkable stability by keeping 50% of residual activity after 100 days storage at room temperature. The enzyme Km and Vmax values were 21.93 mM, 8 U/ml, respectively. To the best of our knowledge, in comparison with the other characterized cysteine proteases, rEla is the only reported cysteine protease with collagen specificity. The enzymes activity increases up to 1.4 times in the presence of calcium ion (2 mM) suggesting it as the enzyme's co-factor. When exposed to surfactants including Tween20, Tween80, Triton X-100 and SDS (1% and 4% v/v) the enzyme activity surprisingly increased up to 5 times.

Protein function analysis of germinated Moringa oleifera seeds, and purification and characterization of their milk-clotting peptidase

The present study aimed to investigate the biological functions of germinated M. oleifera seed proteins and to identify the identity of milk-clotting proteases. A total of 963 proteins were identified, and those with molecular weights between 10 and 30 kDa were most abundant. The identified proteins were mainly involved in energy-associated catalytic activity and metabolic processes, and carbohydrate and protein metabolisms. The numbers of proteins associated with the hydrolytic and catalytic activities were higher than the matured dry M. oleifera seeds reported previously. Of the identified proteins, proteases were mainly involved in the milk-clotting activity. Especially, a cysteine peptidase with a molecular mass of 17.727 kDa exhibiting hydrolase and peptidase activities was purified and identified. The identified cysteine peptidase was hydrophilic, and its secondary structure consisted of 27.60% alpha helix, 9.20% beta fold, and 63.20% irregular curl; its tertiary structure was also constructed using M. oleifera seed 2S protein as the protein template. The optimal pH and temperature of the purified protease were pH 4.0 and 60 °C, respectively. The protease had high acidic stability and good thermostability, thus could potentially be applied in the dairy industry.

Exploring the Milk-Clotting and Proteolytic Activities in Different Tissues of Vallesia glabra: a New Source of Plant Proteolytic Enzymes

Proteolytic enzymes are widely distributed in nature, playing essential roles in important biological functions. Recently, the use of plant proteases at the industrial level has mainly increased in the food industry (e.g., cheesemaking, meat tenderizing, and protein hydrolysate production). Current technological and scientific advances in the detection and characterization of proteolytic enzymes have encouraged the search for new natural sources. Thus, this work aimed to explore the milk-clotting and proteolytic properties of different tissues of Vallesia glabra. Aqueous extracts from the leaves, fruits, and seeds of V. glabra presented different protein profiles, proteolytic activity, and milk-clotting activity. The milk-clotting activity increased with temperature (30-65 °C), but this activity was higher in leaf (0.20 MCU/mL) compared with that in fruit and seed extracts (0.12 and 0.11 MCU/mL, respectively) at 50 °C. Proteolytic activity in the extracts assayed at different pH (2.5-12.0) suggested the presence of different types of active proteases, with maximum activity at acidic conditions (4.0-4.5). Inhibitory studies indicated that major activity in V. glabra extracts is related to cysteine proteases; however, the presence of serine, aspartic, and metalloproteases was also evident. The hydrolytic profile of caseins indicated that V. glabra leaves could be used as a rennet substitute in cheesemaking, representing a new and promising source of proteolytic enzymes.

High-Level Expression and Substrate-Binding Region Modification of a Novel BL312 Milk-Clotting Enzyme To Enhance the Ratio of Milk-Clotting Activity to Proteolytic Activity

A novel BL312 milk-clotting enzyme (MCE) exhibited high-level expression and remarkable milk-clotting activity (MCA) (865 ± 20 SU/mL) that was 3.3-fold higher than the control by optimizing induction conditions in recombinant Escherichia. coli harboring pET24a-proMCE. Through substrate-binding region analyses and modification, MCE-G165A was identified from nine mutants and showed a proteolytic activity of 49.4 ± 2.4 U/mL and an MCA/PA ratio of 18.2, which were respectively 1.9-fold lower and 2.0-fold higher than those of the control. The purified MCE-G165A (28 kDa) exhibited weak α_s-casein, β-casein, and strong κ-casein (κ-CN) hydrolysis levels as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reversed-phase high-performance liquid chromatography. The milk-clotting mechanism for MCE-G165A was the primary hydrolysis of Met106-Ala107 and Asn123-Thr124 bonds in κ-CN, as determined by mass spectrometry. MCE-G165A showed different hydrolysis sites in casein, leading to various functional peptides. Feasible methods for obtaining MCEs suitable as calf rennet substitutes are presented.