Newly Effective Milk-Clotting Enzyme from Bacillus subtilis and Its Application in Cheese Making

A Prototype Process for Demulsification of Waste Ice Cream

Recovery of the butterfat in waste ice cream may be an opportunity to mitigate food and economic loss. Previous efforts to recover such fat have succeeded in producing a fat-enriched fraction but have not succeeded in demulsifying the fat. In the present study, a method involving a sequence of emulsion-breaking steps is shown to be effective for releasing a majority of the fat from waste ice cream as free, unemulsified oil. The effect of altering process conditions including enzyme type, pH, and incubation temperature is reported. Depending on the test conditions and the variety of ice cream used, typically 59%-81% of the fat was recovered, with varying degrees of hydrolytic and oxidative damage. As the method is relatively complex, an experiment which omitted individual processing steps demonstrated that each step was required for high recovery. Success with 4 of 5 tested varieties showed that the method has reasonably broad applicability. The results are compared with those achieved using a standardized solvent extraction method. Finally, the method is evaluated for its potential as the basis for a commercial WIC fat recovery process.

Cell immobilization for enhanced milk clotting enzyme production from Bacillus amyloliquefacien and cheese quality

BACKGROUND

Milk clotting enzymes, essential for milk coagulation in cheese production, are obtained from the stomach of young ruminants, an expensive and limited source. This study was accomplished by finding a suitable alternative. Bacterial isolates recovered from honey were screened for milk clotting enzyme activity. and further, by immobilization of the microorganisms to enhance stability and facilitate their repeated use.

RESULT

The most effective enzyme was produced by a microbe identified as Bacillus amyloliquefaciens based on 16 S rRNA sequencing. The cells were encapsulated in Ca2+ alginate beads. These beads retained complete enzyme production after being used five times. Glucose and Soybean were selected as the most favorable carbon and nitrogen sources, respectively. The optimum temperature for activity was 35 ℃ for both free and immobilized cells but as the temperature was increased to 55 °C and above, the encapsulated form retained more activity than the free cells. The pH optimum shifted from 6.5 to 7 for the free cells to 7-7.5 for the immobilized cells. The immobilization process decreased the activation energy for enzyme production and activity, prolonged the enzyme half-life, and increased the deactivation energy. Enzyme produced by immobilized cells generated a more compact cheese.

CONCLUSIONS

The finding of this study was to identify a less expensive source of milk-clotting enzymes and confirm the success of cell immobilization in improving cell rigidity and stability. Also, immobilization of this B. amyloliquefaciens strain offers an enzyme source of value for industrial production of cheese.

Fe3O4@silica-thermolysin: A robust, advantageous, and reusable microbial nanobiocatalyst for proteolysis and milk-clotting

Thermolysin (TLN) is a microbial highly-priced thermostable metallo-endoprotease with complementary substrate specificity to those of proteases widely used in science and industry for protein digestion and milk-clotting. This study is the first to immobilize TLN on aminated superparamagnetic nanoparticles (Fe3O4@silica-NH2) aiming for higher stability, recoverability, reusability, and applicability in proteolysis and as a microbial rennet-like milk-clotting enzyme. The nanobiocatalyst developed (Fe3O4@silica-TLN) displays hydrolytic activity on a synthetic TLN substrate and, apparently, was fully recovered from reaction media by magnetic decantation. More importantly, Fe3O4@silica-TLN retains TLN catalytic properties in the presence of calcium ions even after exposure to 60 °C for 48 h, storage at 4 °C for 80 days and room temperature for 42 days, use in proteolyses, and in milk-clotting for up to 11 cycles. Its proteolytic activity on bovine milk casein in 24 h furnished 84 peptides, of which 29 are potentially bioactive. Also, Fe3O4@silica-TLN catalyzed the digestion of bovine serum albumin. In conclusion, Fe3O4@silica-TLN showed to be a new, less autolytic, thermostable, non-toxic, magnetically-separable, and reusable nanobiocatalyst with highly attractive properties for both science (peptide/protein chemistry and structure, proteomic studies, and the search for new bioactive peptides) and food industry (cheese manufacture).

New Coagulant Proteases for Cheesemaking from Leaves and Latex of the Spontaneous Plant Pergularia tomentosa: Biochemical Characterization of Coagulants and Sensorial Evaluation of Cheese

The purpose of this study was to evaluate the caseinolytic and milk-clotting activities of aqueous crude extracts from leaves and latex of the Pergularia tomentosa, to determine their suitability as a rennet substitute. These extracts were subjected to a series of biochemical tests before being used in the production of cheese. The results showed that the enzymatic latex extract had a higher coagulant activity than the leaf extract. However, under different clotting conditions (pH, temperature, and CaCl₂ concentration), both coagulants behaved similarly in the coagulation of Berridge substrate. The SDS-PAGE and zymographic analysis revealed identical protein bands with a single active zone in both extracts, corresponding to a molecular weight of 26.98 kDa and 26.03 kDa in the extract of leaf and latex, respectively. Both extracts were stable to different effectors but strongly inhibited by iodoacetamide and Hg, suggesting it to be a cysteine protease. Both extracts were able to hydrolyze casein and generate peptides of 14 kDa, with excessive hydrolysis of the other casein fractions. The physicochemical parameters of cheese made from latex and leaf extract evolved similarly to control cheese. According to the sensory evaluation, cheese made with latex had a mildly bitter flavor but showed a high acceptance rate (>80%).

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.

Characterization of a Novel Milk-Clotting Aspartic Protease from Penicillium sp. and Structural Explanation for its High Milk-Clotting Index

A novel milk-clotting enzyme isolated from Penicillium sp. ACCC 39790 (PsMCE) was prepared by heterologous expression. The recombinant PsMCE had an apparent molecular mass of 45 kDa and exhibited maximum casein hydrolysis activity at pH 4.0 and 50 °C. The PsMCE activity was enhanced by calcium ions and strongly inhibited by pepstatin A. Through hydrolysis pattern and cleavage site analyses, the milk-clotting activity of PsMCE was related to its specific hydrolysis between Phe₁₀₅ and Met₁₀₆ in the κ-casein proteins. The structural basis of PsMCE was characterized using homology modeling, molecular docking, and interactional analysis. The P1' region of PsMCE is critical for its selective binding to the hydrolytic site in κ-casein, and the hydrophobic forces play a decisive role in the specific cleavage of Phe₁₀₅ and Met₁₀₆. These interactional analyses between PsMCE and the ligand peptide clarified the fundamentals of its high milk-clotting index (MCI). PsMCE could be applied in cheese making due to its thermolability and high MCI value as a potential milk-clotting enzyme.

Isolation and production optimization of a novel milk-clotting enzyme Bacillus velezensis DB219

The milk-clotting enzyme (MCE) is a crucial ingredient in cheese manufacture. Due to the limits of traditional MCE, finding viable substitute is a pressing issue. This study aims to isolate and identify a wild strain with high milk-clotting activity (MCA) and low proteolytic activity (PA) and optimize the fermentation conditions for MCE production. A strain of Bacillus velezensis DB219 with high MCA/PA value (9.2) was isolated from dairy soil (Wuchang, Heilongjiang, China) and identified through 16S rRNA from 40 strains. The optimal wheat bran, carbon, nitrogen, inoculum size, volume and initial pH were 60 g/L, soluble starch 12.5 g/L, corn steep liquor 3 g/L, 5%, 40 mL and 6.15, respectively for improving DB219 MCE production through single factor experiment. The wheat bran concentration, corn steep liquor concentration and volume were the most critical factor and their changed range was determined through Plackett–Burman design and the steepest ascent/descent experiments. The response surface analysis experiment of three factors and three levels was conducted by Box–Behnken design. The theoretical optimal fermentation conditions for DB219 MCE were as follows: wheat bran concentration 60.14 g/L, soluble starch 12.5 g/L, corn steep liquor 3 g/L, inoculum size 5%, volume 40.08 mL and initial pH 6.15. DB219 MCE achieved the maximal MCA (3164.84 SU/mL) that was 101.9% of the predicted value (3104.49 SU/mL) and 4.3-fold higher than the control.

Evaluation of Antiradical and Antioxidant Activities of Lipopeptides Produced by Bacillus subtilis Strains

This study investigated the antiradical and antioxidant potential of the three families of lipopeptides (i.e., surfactin, mycosubtilin, and plipastatin/fengycin) produced by Bacillus subtilis strains. The antiradical/antioxidant activities of highly purified lipopeptides were studied in acellular models using a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, superoxide anion (O 2 . - ), hydrogen peroxide, (H2O2) and hydroxyl radical (HO.). At a lipopeptide concentration of 500 mg.L-1, the maximum inhibition of DPPH reached 22.88% (obtained for plipastatin). Moreover, the scavenging effects ofO 2 . - , H2O2, and HO. at the highest concentration tested (250 mg.L-1) were found to be 6, 21, and 3% for surfactin, 19, 9, and 15% for mycosubtilin, 21, 18, and 59% for plipastatin, 21, 31, and 61% for the mixture of surfactin/plipastatin, and 13, 16, and 15% for the mixture of surfactin/mycosubtilin, respectively. These results showed that plipastatin was the best candidate due to its antioxidant activities.

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.

Screening of a Bacillus subtilis strain producing both nattokinase and milk-clotting enzyme and its application in fermented milk with thrombolytic activity

Bacillus subtilis is a generally recognized as safe probiotic, which is used as a starter for natto fermentation. Natto is a functional food with antithrombus function due to nattokinase. Compared with natto, fermented milk is a more popular fermented food, which is commonly fermented by Lactobacillus bulgaricus and Streptococcus. However, there is no report on B. subtilis-fermented milk. In this study, to produce a functional fermented milk with antithrombus function, a B. subtilis strain (B. subtilis JNFE0126) that produced both nattokinase and milk-clotting enzyme was isolated from traditionally fermented natto and used as the starter for the functional fermented milk. In liquid fermentation culture, the peak values of thrombolytic activity and milk-clotting activity were 3,511 U/mL at 96 h and 874.5 Soxhlet unit/mL at 60 h, respectively. The optimal pH and temperature were pH 7.0 at 40°C for nattokinase and pH 6.5 and 55°C for milk-clotting enzyme, respectively. The thrombolytic activity in the fermented milk reached 215.1 U/mL after 8 h of fermentation. Sensory evaluation showed that the acceptance of the milk fermented by B. subtilis JNFE0126 was similar to the traditional milk fermented by L. bulgaricus and S. thermophilus. More importantly, oral intake of the fermented milk by the thrombosis-model mice prevented the development of thrombosis. Our results suggest that B. subtilis JNFE0126-fermented milk has potential as a novel, functional food in the prevention of thrombosis-related cardiovascular diseases.

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.

Study of the Compositional, Microbiological, Biochemical, and Volatile Profile of Red-Veined Cheese, an Internal Monascus-Ripened Variety

Red-Veined Cheese is an experimental internal mold-ripened cheese using red koji powder as the red starter. The objective of this study was to characterize the physicochemical parameters, microorganisms, proteolysis, lipolysis, and volatile profile of the cheese during 33 days of ripening. The gross composition was 56.7% (w/w) for total solids, 45.8% (w/w) for fat-in-dry matter, 2.58% (w/w) for salt content and 37.8% (w/w) for protein. The pH increased from 4.88 to 5.23 during ripening. The Monascus density first rose and then fell, while total mesophilic bacteria count declined steadily throughout the maturation. Proteolysis degree in experimental group was significantly higher than in control group without inoculation of red koji powder. Analysis of the fatty acid profile showed that the internal Monascus-fermentation also promoted lipolysis. A total of 63 volatile compounds, including 12 ketones, 14 alcohols, 15 acids, 13 esters, 5 aldehydes, 3 lactones and 1 phenol, were identified by gas chromatography-mass spectrometry (GC-MS) coupled with headspace solid-phase microextraction (HS-SPME). The main chemical groups of volatile compounds were ketones, alcohols, acids and esters whereas aldehydes, lactones, and phenols represented only minor components. At the end of ripening, the levels of ketones, alcohols, esters were significantly higher in the experimental cheese compared with the control. Our results therefore show that the internal Monascus-fermentation is not only a suitable technology to form red veins in the paste but also an effective method to impact the composition of volatile compounds in cheese, which can thus distinguish it from other internal mold-ripened cheeses and surface-ripened Monascus-fermented cheese.

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.

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.

Biotechnological potential of a cysteine protease (CpCP3) from Calotropis procera latex for cheesemaking

This article reports the characterization and evaluation of the biotechnological potential of a cysteine protease purified from Calotropis procera (CpCP3). This enzyme was highly stable to different metal ions and was able to hydrolyze κ-casein similarly to bovine chymosin. Atomic force microscopy showed that the process of casein micelle aggregation induced by CpCP3 was similar to that caused by chymosin. The cheeses made using CpCP3 showed higher moisture content than those made with chymosin, but protein, fat, and ash were similar. The sensory analysis showed that cheeses made with CpCP3 had high acceptance index (>80%). In silico analysis predicted the presence of only two short allergenic peptides on the surface of CpCP3, which was highly susceptible to digestive enzymes and did not alter zebrafish embryos' morphology and development. Moreover, recombinant CpCP3 was expressed in Escherichia coli. All results support the biotechnological potential of CpCP3 as an alternative enzyme to chymosin.

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.