A Comparative Study of New Aspergillus Strains for Proteolytic Enzymes Production by Solid State Fermentation

Correlation Analysis between Microbial Communities and Flavor Compounds during the Post-Ripening Fermentation of Traditional Chili Bean Paste

Chili bean paste is a traditional flavor sauce, and its flavor compounds are closely related to its microflora. This study focused on investigating the content of bioactive compounds, flavor compounds, and microbial communities during the post-ripening fermentation of chili bean paste, aiming to provide a reference for improving the flavor of chili bean paste by regulating microorganisms. Compared to no post-ripening fermentation, the content of organic acids increased significantly (p < 0.05), especially that of citric acid (1.51 times). Glutamic acid (Glu) was the most abundant of the 17 free amino acids at 4.0 mg/g. The aroma profiles of the samples were significantly influenced by fifteen of the analyzed volatile compounds, especially methyl salicylate, methyl caproate, and 2-octanol (ROAV > 1). Latilactobacillus (27.45%) and Pseudomonas (9.01%) were the dominant bacterial genera, and Starmerella (32.95%) and Pichia (17.01%) were the dominant fungal genera. Weissella, Lacticaseibacillus, Pichia, and Kazachstania had positive effects on volatile flavoring compounds, which enriched the texture and flavor of the chili bean paste. Therefore, the microbial-community activity during the post-ripening fermentation is the key to enhance the flavor quality of the product.

Production and characterization of protease enzyme from Acinetobacter pittii using peanut meal as substrate

A significantly high protease enzyme yield of 617 U/ml was achieved with Acinetobacter pittii as the microorganism and peanut oil meal as the substrate. Peanut oil meal, which consists of proteins (40-60%) and carbohydrates (22-30%), serves as a sufficient source of nitrogen and carbon necessary for microbial growth and production of enzymes. Moreover, peanut meal offers the advantages of being affordable and available in large quantities, making the meal suitable for cost-effective enzyme production. In the present study, two bacterial strains and one fungal strain were selected to produce proteases utilizing peanut oil meal as the substrate. The experimental conditions during the enzyme production, including pH and temperature, were optimized. In addition, the substrate was enriched with various carbon and nitrogen sources. The microbial strains were streaked on nutritional agar (for bacteria) and potato dextrose agar (for fungus). Following an incubation period, the plates were stored at 4°C for further studies. The molecular weight of partially purified proteases of Acinetobacter pittii was found to be ≅ 95.5 kDa. Potassium nitrate was the most ideal nitrogen source (up to 411% increase in activity) and fructose was the best carbon source (425% increase). These enzymes exhibited excellent temperature tolerance and were capable of functioning over a wide pH range. Furthermore, the obtained proteases demonstrated ability to coagulate milk effectively, indicating their potential for various food-related applications.

From microbes to molecules: a review of microbial-driven antioxidant peptide generation

Oxidative stress, arising from excess reactive oxygen species (ROS) or insufficient antioxidant defenses, can damage cellular components, such as lipids, proteins, and nucleic acids, resulting in cellular dysfunction. The relationship between oxidative stress and various health disorders has prompted investigations into potent antioxidants that counteract ROS's detrimental impacts. In this context, antioxidant peptides, composed of two to twenty amino acids, have emerged as a unique group of antioxidants and have found applications in food, nutraceuticals, and pharmaceuticals. Antioxidant peptides are sourced from natural ingredients, mainly proteins derived from foods like milk, eggs, meat, fish, and plants. These peptides can be freed from their precursor proteins through enzymatic hydrolysis, fermentation, or gastrointestinal digestion. Previously published studies focused on the origin and production methods of antioxidant peptides, describing their structure-activity relationship and the mechanisms of food-derived antioxidant peptides. Yet, the role of microorganisms hasn't been sufficiently explored, even though the production of antioxidant peptides frequently employs a variety of microorganisms, such as bacteria, fungi, and yeasts, which are recognized for producing specific proteases. This review aims to provide a comprehensive overview of microorganisms and their proteases participating in enzymatic hydrolysis and microbial fermentation to produce antioxidant peptides. This review also covers endogenous peptides originating from microorganisms. The information obtained from this review might guide the discovery of novel organisms adept at generating antioxidant peptides.

Unconventional microbial proteases as promising tools for the production of bioactive protein hydrolysates

Enzymatic hydrolysis is the most prominent strategy to release bioactive peptides from different food proteins and protein-rich by-products. Unconventional microbial proteases (UMPs) have gaining increased attention for such purposes, particularly from the 2010s. In this review, we present and discuss aspects related to UMPs production, and their use to obtain bioactive protein hydrolysates. Antioxidant and anti-hypertensive potentials, commonly evaluated through in vitro testing, are mainly reported. The in vivo bioactivities of protein hydrolysates and peptides produced through UMPs action are highlighted. In addition to bioactivities, enzymatic hydrolysis acts by modulating the functional properties of proteins for potential food uses. The compiled literature indicates that UMPs are promising biocatalysts to generate bioactive protein hydrolysates, adding up to commercially available enzymes. From the recent interest on this topic, continuous and in-depth research is needed to advance toward the applicability and commercial utility of both UMPs and obtained hydrolysates.

Aspartic protease-pepstatin A interactions: Structural insights on the thermal inactivation mechanism

Aspartic proteases are the targets for structure-based drug design for their role in physiological processes and pharmaceutical applications. Structural insights into the thermal inactivation mechanism of an aspartic protease in presence and absence of bound pepstatin A have been obtained by kinetics of thermal inactivation, CD, fluorescence spectroscopy and molecular dynamic simulations. The irreversible thermal inactivation of the aspartic protease comprised of loss of tertiary and secondary structures succeeded by the loss of activity, autolysis and aggregation The enthalpy and entropy of thermal inactivation of the enzyme in presence of pepstatin A increased from 81.2 to 148.5 kcal mol^-1, and from 179 to 359 kcal mol^-1 K^-1 respectively. Pepstatin A shifted the mid-point of thermal inactivation of the protease from 58 °C to 77 °C. The association constant (K) for pepstatin A with aspartic protease was 2.5 ± 0.3 × 10 ⁵ M^-1 and ΔG^o value was -8.3 kcal mol^-1. Molecular dynamic simulation studies were able to delineate the role of pepstatin A in stabilizing backbone conformation and side chain interactions. In the Cα-backbone, the short helical segments and the conserved glycines were part of the most unstable segments of the protein. Understanding the mechanism of thermal inactivation has the potential to develop re-engineered thermostable proteases.

Production of Alkaline Proteases using Aspergillus sp. Isolated from Injera: RSM-GA Based Process Optimization and Enzyme Kinetics Aspect

Alkaline proteases are well known to be significant industrial enzymes. This study focused on isolating the fungus producing proteases from, a typical Ethiopian food, Injera. Further, the process optimization for protease production using response surface methodology (RSM) and the characterization of the acquired protease were investigated. The 18S rDNA gene sequence homology of the fungus isolate revealed that it was Aspergillus sp. Further, it was deposited in NCBI GenBank with accession number MK4262821. Using the isolate, owing to maximize the protease production, the independent process parameters, temperature, pH, and sucrose concentration were optimized using RSM followed by a genetic algorithm (GA). Based on the statistical approach by RSM-GA optimization, maximum enzyme activity (166.4221 U/ml) was found at 30.5 °C, pH 8.24, and 0.316% sucrose concentration. Also, the crude cocktail of enzymes acquired from optimal condition was partially purified using ammonium which showed that the increased activity by 1.96-fold. Considerably, the partially purified enzyme exhibited stable performance during the temperature range 30-60 °C, pH range 7-10, and NaCl concentration of 0.5-2 mM. Also, the antioxidant activity, degree hydrolysis for the protein, Michaelis-Menten (M-M) kinetic parameters, and activation energy were determined for the obtained enzyme cocktail. It showed that the M-M kinetic parameters, Km (5.54 mg/ml), and Vmax (24.44 mg/ml min) values were observed. Using Arrhenius law, the value of activation energy for the enzyme cocktail was determined as 32.42 kJ/mol.

The Change Mechanism of Structural Characterization and Thermodynamic Properties of Tannase from Aspergillus niger NL112 Under High Temperature

Tannase from Aspergillus niger NL112 was purified 5.1-fold with a yield of 50.44% via ultrafiltration, DEAE-Sepharose Fast Flow column chromatography, and Sephadex G-100 column chromatography. The molecular weight of the purified tannase was estimated as 45 kDa. The optimum temperature and pH for its activity were 45 °C and 5.0, respectively. The results of circular dichroism, FT-IR (Fourier transform infrared) spectroscopy, and fluorescence spectra indicated that high temperature could lead to the change of tannase secondary and tertiary structures. Tannase had a greater affinity for tannic acid at 40 °C with a K_m value of 2.12 mM and the greatest efficiency hydrolysis (K_cat/K_m) at 45 °C. The rate of inactivation (k) increased with the increase of temperature and the half-life (t_1/2) gradually decreased. It was found to be 1.0 of the temperature quotient (Q₁₀) value for tannic acid hydrolysis by tannase. The thermodynamic parameters of the interaction system were calculated at various temperatures. The positive enthalpy (ΔH) values and decreasing ΔH values with the increase of temperature indicated that the hydrolysis of tannase was an endothermic process. Our results indicated that elevated temperature could change the tertiary structure of tannase and reduce its thermostability, which caused a gradual decrease of tannase activity with an increase in temperature.

Vermiculite as a new carrier for extracellular protease production by Aspergillus spp. under solid-state fermentation

A new method has been developed to increase the productivity of aspergilli - producers of extracellular proteinases based on their cultivation on vermiculite under solid-state fermentation conditions. The productivity of the mycelium Aspergillus ochraceus L-1 and Aspergillus ustus 1 was 3-18 times higher not only in comparison with submerged cultivation, but also in comparison with growth on other carriers studied under solid-state fermentation conditions. Vermiculite can be considered as a new promising carrier for solid-state fermentation of micromycetes.

Physicochemical, flavor and microbial dynamic changes during low-salt doubanjiang (broad bean paste) fermentation

This study aimed to elaborate the roles of salt concentration on doubanjiang (broad bean paste) fermentation. Three sets of doubanjiang samples which had lower salt concentration than commercial doubanjiang were prepared and the physicochemical parameters, biogenic amines, flavor, microbial dynamics were analyzed during fermentation. The salt reduction showed significant effect on the dynamics of bacteria and fungi, thus leading to doubanjiang samples with different properties. Salt reduction during fermentation relieved the osmotic pressure towards microbes, which favored the accumulation of amino acid nitrogen, amino acids, and volatile flavor compounds. However, higher concentrations of total acids and biogenic amines and the existence of conditional pathogens, such as Klebsiella, Cronobacter and Acinetobacter genera, were observed in salt reduced doubanjiang samples, which was undesirable for doubanjiang quality. This study would deep our understanding of the roles of salt on doubanjiang fermentation.

Biocontrol of Two Bacterial Inoculant Strains and Their Effects on the Rhizosphere Microbial Community of Field-Grown Wheat

Biocontrol by inoculation with beneficial microbes is a proven strategy for reducing the negative effect of soil-borne pathogens. We evaluated the effects of microbial inoculants BIO-1 and BIO-2 in reducing soil-borne wheat diseases and in influencing wheat rhizosphere microbial community composition in a plot test. The experimental design consisted of three treatments: (1) Fusarium graminearum F0609 (CK), (2) F. graminearum + BIO-1 (T1), and (3) F. graminearum F0609 + BIO-2 (T2). The results of the wheat disease investigation showed that the relative efficacies of BIO-1 and BIO-2 were up to 82.5% and 83.9%, respectively. Illumina MiSeq sequencing revealed that bacterial abundance and diversity were significantly higher (P < 0.05) in the treatment groups (T1 and T2) than in the control, with significantly decreased fungal diversity in the T2 group. Principal coordinates and hierarchical clustering analyses revealed that the bacterial and fungal communities were distinctly separated between the treatment and control groups. Bacterial community composition analysis demonstrated that beneficial microbes, such as Sphingomonas, Bacillus, Nocardioides, Rhizobium, Streptomyces, Pseudomonas, and Microbacterium, were more abundant in the treatment groups than in the control group. Fungal community composition analysis revealed that the relative abundance of the phytopathogenic fungi Fusarium and Gibberella decreased and that the well-known beneficial fungi Chaetomium, Penicillium, and Humicola were more abundant in the treatment groups than in the control group. Overall, these results confirm that beneficial microbes accumulate more easily in the wheat rhizosphere following application of BIO-1 and BIO-2 and that the relative abundance of phytopathogenic fungi decreased compared with that in the control group.

Kinetics, detergent compatibility and feather-degrading capability of alkaline protease from Bacillus subtilis AKAL7 and Exiguobacterium indicum AKAL11 produced with fermentation of organic municipal solid wastes

Alkaline proteases having activity and stability at alkaline pH possess a large variety of applications in many industries. Growing renewed interest urges the need to find a single alkaline protease with promising properties to be used in different industrial processes. Herein, alkaline proteases produced through fermentation of cheap and easily available organic municipal solid wastes by Bacillus subtilis AKAL7 and Exiguobacterium indicum AKAL11 were purified to investigate their kinetic and thermodynamic parameters, detergent compatibility, dehairing and feather-degrading capability. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that the purified protease from B. subtilis and E. indicum had molecular mass of ∼45 and 75 kDa, respectively. The protease from B. subtilis and E. indicum showed highest activity at 55 and 50 °C having low K _m 1.17 and 0.567 mg/mL and high V _max 416.67 and 333.33 µmole/min, respectively. The activation energy and temperature quotient of protease from B. subtilis and E. indicum were 26.52 and 65.75 kJ/mole, and 1.0004 and 1.0003 at 20-55 and 20-50 °C, respectively. Thermodynamics analysis revealed the formation of more ordered enzyme-substrate complexes along with spontenity of enzyme reaction. The protease from E. indicum exhibited better compatibility at higher concentration of detergents compared to that from B. subtilis. However, both proteases could retain more than 80% of the activity in the presence of 0.1% commercial laundry detergents. The purified protease from the both sources could degrade almost 90% of barbs and 40% of dry weight of the native feather and that from E. indicum could dehair cow skin. Results reported herein suggest that the alkaline protease from B. subtilis AKAL7 and E. indicum AKAL11 has biotechnological implications in detergent, leather and poultry feather processing industries.

An overview on bioethanol production from lignocellulosic feedstocks

Lignocellulosic ethanol has been proposed as a green alternative to fossil fuels for many decades. However, commercialization of lignocellulosic ethanol faces major hurdles including pretreatment, efficient sugar release and fermentation. Several processes were developed to overcome these challenges e.g. simultaneous saccharification and fermentation (SSF). This review highlights the various ethanol production processes with their advantages and shortcomings. Recent technologies such as singlepot biorefineries, combined bioprocessing, and bioenergy systems with carbon capture are promising. However, these technologies have a lower technology readiness level (TRL), implying that additional efforts are necessary before being evaluated for commercial availability. Solving energy needs is not only a technological solution and interlinkage of various factors needs to be assessed beyond technology development.

Partial purification and characterization of serine protease produced through fermentation of organic municipal solid wastes by Serratia marcescens A3 and Pseudomonas putida A2

Proteolytic bacteria isolated from municipal solid wastes (MSW) were identified as Serratia marcescens A3 and Pseudomonas putida A2 based on 16S rDNA sequencing. Protease produced through fermentation of organic MSW by these bacteria under some optimized physicochemical parameters was partially purified and characterized. The estimated molecular mass of the partially purified protease from S. marcescens and P. putida was approximately 25 and 38 kDa, respectively. Protease from both sources showed low Km 0.3 and 0.5 mg ml-1 and high Vmax 333 and 500 µmole min-1 at 40 °C, and thermodynamics analysis suggested formation of ordered enzyme-substrate (E-S) complexes. The activation energy (Ea) and temperature quotient (Q10) of protease from S. marcescens and P. putida were 16.2 and 19.9 kJ/mol, and 1.4 and 1.3 at temperature range from 20 to 40 °C, respectively. Protease of the both bacterial isolates was serine and cysteine type. The protease retained approximately 97% of activity in the presence of sodium dodecyl sulphate. It was observed that the purified protease of S. marcescens could remove blood stains from white cotton cloth and degrade chicken flesh remarkably. Our study revealed that organic MSW can be used as raw materials for bacterial protease production and the protease produced by S. marcescens A3 might be potential for applications.

Pectinase production by Aspergillus giganteus in solid-state fermentation: optimization, scale-up, biochemical characterization and its application in olive-oil extraction

The application of pectinases in industrial olive-oil processes is restricted by its production cost. Consequently, new fungal strains able to produce higher pectinase titers are required. The aim of this work was to study the capability of Aspergillus giganteus NRRL10 to produce pectinolytic enzymes by SSF and evaluate the application of these in olive-oil extraction. A. giganteus was selected among 12 strains on the basis of high pectinolytic activity and stability. A mixture composed by wheat bran, orange, and lemon peels was selected as the best substrate for enzyme production. Statistical analyses of the experimental design indicated that pH, temperature, and CaCl2 are the main factors that affect the production. Subsequently, different aeration flows were tested in a tray reactor; the highest activity was achieved at 20 L min−1 per kilogram of dry substrate (kgds). Finally, the pectinolytic enzymes from A. giganteus improved the oil yield and rheological characteristics without affecting oil chemical properties.