Thermostable acidic protease production inAspergillus terreusNCFT 4269.10 using chickling vetch peels

Starter molds and multi-enzyme catalysis in koji fermentation of soy sauce brewing: A review

Soy sauce is a traditional fermented food produced from soybean and wheat under the action of microorganisms. The soy sauce brewing process mainly involves two steps, namely koji fermentation and moromi fermentation. In the koji fermentation process, enzymes from starter molds, such as protease, aminopeptidase, carboxypeptidase, l-glutaminase, amylase, and cellulase, hydrolyze the protein and starch in the raw ingredients to produce short-chain substances. However, the enzymatic reactions may be diminished after being subjected to moromi fermentation due to its high NaCl concentration. These enzymatically hydrolyzed products are further metabolized by lactic acid bacteria and yeasts during the moromi fermentation process into organic acids and aromatic compounds, giving soy sauce a unique flavor. Thus, the starter molds, such as Aspergillus oryzae, Aspergillus sojae, and Aspergillus niger, and their secreted enzymes play crucial roles in soy sauce brewing. This review comprehensively covers the characteristics of the starter molds mainly used in soy sauce brewing, the enzymes produced by starter molds, and the roles of enzymes in the degradation of raw material. We also enumerate current problems in the production of soy sauce, aiming to offer some directions for the improvement of soy sauce taste.

Study of protease activity from Aspergillus awamori INCQS2B.361U2/1 extracellular fraction and modification of culture medium composition to isolate a novel aspartic protease

Aspergillus awamori was cultivated in a modified Breccia medium, and the extracellular fraction was obtained, which presented 260 ± 15 µg of protein/mg and specific protease activity of 3.87 ± 0.52 mM.min^-1.mg of protein^-1 using N_α-p-tosyl-L-arginine methyl ester hydrochloride (_L-TAME) as substrate. This fraction showed major proteins about 104 and 44 kDa and maximal protease activity at pH 5.5, 6.5, and 9.0, suggesting that A. awamori secretes acidic, neutral, and alkaline proteases with expressive thermal stability, however, aspartic protease was the most important activity. When yeast extract was supplemented to a modified Breccia medium, A. awamori protein secretion and protease activity were maximal and the affinity chromatography on pepstatin-agarose was employed to isolate the aspartic protease activity, which was called ASPA, with approximately 75 kDa. ASPA maximal activity was obtained at pH 4.5 and 6.5, and 50 °C. Pepstatin inhibited about 80% of ASPA activity, with IC₅₀ and Ki values of 0.154 and 0.072 μM, respectively. ASPA cleaved protein and peptides substrates with the highest activity against gelatin (95 U/mg) and good peptidase activity with K_M 0.0589 mM and V_max 1.909 mM.min^-1.mg protein^-1, using _L-TAME as substrate. A. awamori extracellular fraction is a source of proteases with important activity, and the supplementation of modified Breccia medium increased the aspartic protease production. This enzyme presented different biochemical characteristics from the previously reported A. awamori aspartic proteases. Therefore, ASPA is an excellent candidate for biotechnological application due to its important activity and thermostability.

Optimisation of Xylanase–Pectinase Cocktail Production with Bacillus amyloliquefaciens ADI2 Using a Low-Cost Substrate via Statistical Strategy

An effective statistical tool for increasing and boosting the production of xylanase and pectinase by Bacillus amyloliquefaciens ADI2 during submerged fermentation (SmF) appears to be the response of surface methodology (RSM) using the central composite design (CCD). Optimum production was achieved under fermentation conditions of a temperature of 28 °C, pH of 8.38, inoculum size of 4% (w/v) and agitation speed of 94 rpm for 48 h. The experimental responses demonstrated a near agreement with the expected responses under optimum conditions of independent variables, suggesting the model’s validity. The optimised CCD model had a 1.34-fold, 159 ± 6 U/mL greater xylanase and 5.96-fold, 205 ± 9 U/mL greater pectinase production than the one factor at a time (OFAT) approach. The production of concurrent enzymes of xylanase–pectinase resulted in a ratio of 1:1.3.

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

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

Discovery of Novel Cyclic Salt Bridge in Thermophilic Bacterial Protease and Study of its Sequence and Structure

The plausible explanation behind the stability of thermophilic protein is still yet to be defined more clearly. Here, an in silico study has been undertaken by investigating the sequence and structure of protease from thermophilic (tPro) bacteria and mesophilic (mPro) bacteria. Results showed that charged and uncharged polar residues have higher abundance in tPro. In extreme environment, the tPro is stabilized by high number of isolated and network salt bridges. A novel cyclic salt bridge is also found in a structure of tPro. High number of metal ion-binding site also helps in protein stabilization of thermophilic protease. Aromatic-aromatic interactions also play a crucial role in tPro stabilization. Formation of long network aromatic-aromatic interactions also first time reported here. Finally, the present study provides a major insight with a newly identified cyclic salt bridge in the stability of the enzyme, which may be helpful for protein engineering. It is also used in industrial applications for human welfare.