Breeding and identification of novel koji molds with high activity of acid protease by genome recombination between Aspergillus oryzae and Aspergillus niger

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.

The latest advances on soy sauce research in the past decade: Emphasis on the advances in China

As an indispensable soybean-fermented condiment, soy sauce is extensively utilized in catering, daily cooking and food industry in East Asia and Southeast Asia and is becoming popular in the whole world. In the past decade, researchers began to pay great importance to the scientific research of soy sauce, which remarkably promoted the advances on fermentation strains, quality, safety, function and other aspects of soy sauce. Of them, the screening and reconstruction of Aspergillus oryzae with high-yield of salt and acid-tolerant proteases, mechanism of soy sauce flavor formation, improvement of soy sauce quality through the combination of novel physical processing technique and microbial/enzyme, separation and identification of soy sauce functional components are attracting more attention of researchers, and related achievements have been reported continually. Meanwhile, we pointed out the drawbacks of the above research and the future research directions based on published literature and our knowledge. We believe that this review can provide an insightful reference for international related researchers to understand the advances on soy sauce research.

The regulation of key flavor of traditional fermented food by microbial metabolism: A review

The beneficial microorganisms in food are diverse and complex in structure. These beneficial microorganisms can produce different and unique flavors in the process of food fermentation. The unique flavor of these fermented foods is mainly produced by different raw and auxiliary materials, fermentation technology, and the accumulation of flavor substances by dominant microorganisms during fermentation. The succession and metabolic accumulation of microbial flora significantly impacts the distinctive flavor of fermented foods. The investigation of the role of microbial flora changes in the production of flavor substances during fermentation can reveal the potential connection between microbial flora succession and the formation of key flavor compounds. This paper reviewed the evolution of microbial flora structure as food fermented and the key volatile compounds that contribute to flavor in the food system and their potential relationship. Further, it was a certain guiding significance for food industrial production.

Biological Disease Control by Beneficial (Micro)Organisms: Selected Breakthroughs in the Past 50 Years

Biological control of plant disease by beneficial (micro)organisms is one of the main tools available to preserve plant health within the wider context of One Health and in line with the goals of the Agenda 2030 for Sustainable Development. The commercial development of biocontrol agents, together with a new perspective on the resident microbial community, all supported by innovative "omics" technologies, continues to gain in prominence in plant pathology, addressing the need to feed the increasing world population and to assure safe and secure access to food. The present review considers selected advances within the last 50 years, highlighting those that can be considered as breakthroughs for the biological control research field. Selected examples of successful biocontrol agents and strategies are reported, including the history of the progress in researching Trichoderma isolates as commercial biocontrol agents, the exploitation of mycoviruses to confer hypovirulence to plant pathogenic fungi, the role of microbial communities in the suppressiveness of soils, and evolving approaches including the establishment of synthetic microbial communities.

Phenotypic, Genomic, and Transcriptomic Comparison of Industrial Aspergillus oryzae Used in Chinese and Japanese Soy Sauce: Analysis of Key Proteolytic Enzymes Produced by Koji Molds

Aspergillus oryzae, which generates numerous enzymes for the breakdown of raw materials, is an essential koji mold in soy sauce production. For better soy sauce productivity and flavor quality, China and Japan have developed their own industrial A. oryzae strains at distinct evolutionary branches for use in soy sauce production for decades. However, systematic comparison between the two national industrial strains has been poorly conducted, and thus we have not been able to generate adequate knowledge, especially regarding what are the key hydrolytic enzymes produced by A. oryzae during koji production. This study sequenced and assembled three high-quality genome sequences of industrial A. oryzae originating from China and Japan. Based on the genome sequences, a phylogenetic tree analysis was performed and revealed the evolutional distances between the two national industrial koji molds. Meanwhile, a comparative phenotypic analysis revealed that the two national industrial strains differed in growth and catalytic characteristics, particularly in proteolytic enzyme activities. To investigate the molecular mechanism underlying the phenotypic difference, we conducted systematic comparative genome and transcriptome investigations. We found minor differences in the quantity and diversity of proteolytic enzyme genes between Chinese and Japanese koji molds, while the protease secretion ratio and transcriptional level were dissimilar. We identified 58 potential important enzymes associated with high protein breakdown efficiency during industrial koji fermentation by combining comparative phenotypic and transcriptome data. More research is required to confirm the function of these putative key hydrolytic enzymes. IMPORTANCE Aspergillus oryzae is widely used as an industrial koji mold for soy sauce brewing due to its powerful raw material decomposition capability. Although various proteases in A. oryzae have been identified, it remains a challenge to find essential enzymes involved in soy sauce production. Generally, the industrial A. oryzae used in soy sauce brewing has excellent proteolytic activity. Based on this, we analyzed key proteolytic enzymes according to a comparison of the genome and transcriptome between three industrial strains. This study found little difference in gene numbers and mutations of proteolytic enzymes between three industrial A. oryzae strains. However, variations in protease secretion ratio and transcriptome were discovered between industrial strains. Based on that, we generated 58 candidate key proteolytic enzymes. This work comprehensively analyzed three industrial koji molds, revealing genome development under separate artificial domestication and helping in the study of key proteolytic enzymes during soy sauce production.

Production of Prunin and Naringenin by Using Naringinase from Aspergillus oryzae NYO-2 and Their Neuroprotective Properties and Debitterization

Naringin is a flavanone glycoside in citrus fruits that has various biological functions. However, its bitterness affects the quality, economic value, and consumer acceptability of citrus products. Deglycosylation of naringin using naringinase decreases its bitterness and enhances its functional properties. In this study, eight microbial strains with naringinase activity were isolated from 33 yuzu-based fermented foods. Among them, naringinase from Aspergillus oryzae NYO-2, having the highest activity, was used to produce prunin and naringenin. Under optimal conditions, 19 mM naringin was converted to 14.06 mM prunin and 1.97 mM naringenin. The bitterness of prunin and naringenin was significantly decreased compared to naringin using the human bitter taste receptor TAS2R39. The neuroprotective effects of prunin and naringenin on human neuroblastoma SH-SY5Y cells treated with scopolamine were greater than that of naringin. These findings can widen the potential applications of deglycosylation of naringin to improve sensory and functional properties.

The ancient koji mold (Aspergillus oryzae) as a modern biotechnological tool

Aspergillus oryzae (A. oryzae) is a filamentous micro-fungus that is used from centuries in fermentation of different foods in many countries all over the world. This valuable fungus is also a rich source of many bioactive secondary metabolites. Moreover, A. oryzae has a prestigious secretory system that allows it to secrete high concentrations of proteins into its culturing medium, which support its use as biotechnological tool in veterinary, food, pharmaceutical, and industrial fields. This review aims to highlight the significance of this valuable fungus in food industry, showing its generosity in production of nutritional and bioactive metabolites that enrich food fermented by it. Also, using A. oryzae as a biotechnological tool in the field of enzymes production was described. Furthermore, domestication, functional genomics, and contributions of A. oryzae in functional production of human pharmaceutical proteins were presented. Finally, future prospects in order to get more benefits from A. oryzae were discussed.

Bioconversion of soy under the influence of Aspergillus oryzae strains producing hydrolytic enzymes

Introduction. The fungus Aspergillus oryzae is widely used in the production of fermented soy-based products. However, there is little data on how its genetic characteristics affect the biochemical and fractional composition of protein substances during fermentation and the quality of fermented products. This study aimed to investigate the conversion of soy meal under the influence of two A. oryzae strains with different morphological and cultural properties during the production of a fermented soy sauce. Study objects and methods. The study used two A. oryzae strains, RCAM 01133 and RCAM 01134, which were isolated from the industrial F-931 strain (Russian Collection of Industrial Microorganisms), a producer of hydrolytic enzymes. Micromycetes were cultivated by a solid-phase method on soy meal, followed by dry fermentation. The results were analyzed with regard to accumulation of amine nitrogen, bound and free amino acids, proteins and carbohydrates. Results and discussion. The cultivation of micromycetes resulted in a 35–38% increase in protein, a tenfold increase in free amino acids, and a 1.5–1.7 fold decrease in polysaccharides. The contents of essential amino acids in the fermented soy sauce were 1.7 and 1.2 times as high as in the initial medium (soy meal) and in the reference protein, respectively. Fermentation enhanced the biological value of proteins, increasing the amino acid scores of phenylalanine (7.3–7.7 times), phenylalanine (2 times), as well as valine, threonine, tryptophan, and lysine. The contents of protein and essential amino acids were slightly higher in the sauce with the RCAM 01133 strain. Conclusion. Fermenting soy materials with the RCAM 01133 strain of A. oryzae is an alternative way to produce food ingredients with good sensory properties containing carbohydrates and biologically complete protein in easily digestible forms.

Effect of aroma-producing yeasts in high-salt liquid-state fermentation soy sauce and the biosynthesis pathways of the dominant esters

Fermentation with excellent aroma-producing yeasts can enhance the flavour of soy sauce. In this work, Millerozyma farinosa CS2.23, Zygosaccharomyces rouxii CS2.42, and Candida parapsilosis CS2.53 were added to the high-salt liquid-state moromi to promote soy sauce fermentation. All three yeasts improved the TE of soy sauce, the highest of which reached 1.03 g/L with added CS2.42. Other quality indexes of soy sauce, including RS, TA, and AN, were not greatly affected. The volatile esters of soy sauce added to the three yeasts increased by 108.85%, 166.71%, and 113.61% compared with the control through GC-MS analysis. Obviously, CS2.42 had an excellent ability to produce esters. Studying the biosynthesis pathway of esters, CS2.42 has the best esterification ability, while CS2.53 has the advantage of alcoholysis ability. The exploration of the biosynthetic pathway of acetate and ethyl esters has laid a foundation for regulating esters in soy sauce fermentation.

Enhancement of Acid Protease Activity of Aspergillus oryzae Using Atmospheric and Room Temperature Plasma

Atmospheric and room temperature plasma (ARTP) system is a novel and efficient mutagenesis protocol for microbial breeding. In this study, ARTP was employed to treat spores of Aspergillus oryzae strain 3.042 for selection of high acid protease producers. With an irradiation time of 150 s at the lethal rate of 90%, 19 mutants with higher acid protease activity were initially selected based on different mutant colony morphology and ratio of the clarification halo of protease activity to the colony diameter. Measurements of the acid protease activity revealed that mutant strain B-2 is characterized by a steady hereditary stability with increased acid protease, neutral protease and total protease activities of 54.7, 17.3, and 8.5%, respectively, and decreased alkaline protease activity of 8.1%. In summary, the identified mutant strain B-2 exhibits great potential for the enhancement of the insufficient acid protease activity during the middle and later stages of soy sauce fermentation.

Fermentation of high-salt liquid-state soy sauce without any additives by inoculation of lactic acid bacteria and yeast

Food additives are artificial or natural substances that are added to food to improve the color, aroma, taste, and other qualities, and to meet processing requirements. For the concern of food health and safety, brewed soy sauce without additives has attracted consumers' attention. Here, only four necessary raw materials including soybean, wheat, salt, and water were added. High-salt soy sauce fermentation was conducted for six months by sequential inoculation of lactic acid bacteria and yeast under different brine content (18%, 20%, and 22%). By analyzing the physicochemical indicators during moromi, three soy sauces (No. 1: 18% salt, inoculated with Tetragenococcus halophilus and Zygosaccharomyces rouxii, No. 5: 20% salt, inoculated with T. halophilus and Z. rouxii, No. 11: 22% salt, inoculated with T. halophilus and Candida versatilis) were selected and sterilized to produce finished products for further comparative investigation. Results showed that the flavor components of these three soy sauces were richer in variety than the commercial soy sauces and No. 11 soy sauce was detected to have the largest total amount of organic acids. Plate count agar analysis revealed that the free amino acid differences of soy sauces were distinct, among which the No. 11 soy sauce had the highest glutamate content of 19.64 g L^-1. Besides, it was found that the shelf life of these three soy sauces could reach two years at 4 ℃. This study suggests that the high-salt soy sauce made by rational application of lactic acid bacteria, yeast, and effective sterilization can have high quality and long shelf life without adding any additives.

Functional Genomics of Aspergillus oryzae: Strategies and Progress

Aspergillus oryzae has been used for the production of traditional fermentation and has promising potential to produce primary and secondary metabolites. Due to the tough cell walls and high drug resistance of A. oryzae, functional genomic characterization studies are relatively limited. The exploitation of selection markers and genetic transformation methods are critical for improving A. oryzae fermentative strains. In this review, we describe the genome sequencing of various A. oryzae strains. Recently developed selection markers and transformation strategies are also described in detail, and the advantages and disadvantages of transformation methods are presented. Lastly, we introduce the recent progress on highlighted topics in A. oryzae functional genomics including conidiation, protein secretion and expression, and secondary metabolites, which will be beneficial for improving the application of A. oryzae to industrial production.

Genomic and transcriptomic comparison of Aspergillus oryzae strains: a case study in soy sauce koji fermentation

The filamentous fungus Aspergillus oryzae is used in soy sauce koji making due to its high productivity of hydrolytic enzymes. In this study, we compared the genomes and transcriptomes of an industrial strain RD2 and a strain with decreased fermentation performance TS2, aiming to explain their phenotypic differences at the molecular level. Under the regulation of conidiation and fermentation conditions, the enhanced hydrolytic enzyme production and flavor precursor formation in RD2 described a complete expression profile necessary to maintain desirable fermentation performance. By contrast, central carbon metabolism was up-regulated in TS2 for fast growth, suggesting a conflicting relationship between mycelium growth and fermentation performance. Accumulation of mutations also lowered the fermentation performance of TS2. Our study has deepened the understanding of the metabolism and related regulatory mechanisms in desirable koji fermentation. A list of potential molecular markers identified here could facilitate targeted strain maintenance and improvement for better koji fermentation.

Strain improvement of Aspergillus sojae for increased l-leucine aminopeptidase and protease production

Conventional random mutagenesis was implemented to improve l-leucine aminopeptidase (LAP) and protease production in Aspergillus sojae. Through successive mutagenesis by ethyl methanesulfonate (EMS), UV, and 1-methyl-2-nitro-1-nitrosoguanidine (NTG), EMS25, EU36, and EUN13 mutants from each mutagenesis process were screened using a newly developed quick and easy screening method. The mutant EUN13 exhibited a 9.6-fold increase in LAP [50.61 ± 4.36 U/g-initial dried substrate (IDS)] and a 3.8-fold increase in protease production (13.36 ± 0.31 U/g-IDS) on solid-state fermentation. This mutant showed more frequent branching and higher lap1 mRNA expression as compared to the parent strain SMF 131, which at least in part contributed to the increased LAP and protease production. The mutant EUN13 can be used as a starter organism for diverse industrial soybean fermentation processes for the production of conventional products such as meju, doenjang, and ganjang as well as for the production of new fermented soybean-based sauces.

Microbe participation in aroma production during soy sauce fermentation

Soy sauce is a traditional Japanese fermented seasoning that contains various constituents such as amino acids, organic acids, and volatiles that are produced during the long fermentation process. Although studies regarding the correlation between microbes and aroma constituents have been performed, there are no reports about the influences of the microbial products, such as lactic acid, acetic acid, and ethanol, during fermentation. Because it is known that these compounds contribute to microbial growth and to changes in the constituent profile by altering the moromi environment, understanding the influence of these compounds is important. Metabolomics, the comprehensive study of low molecular weight metabolites, is a promising strategy for the deep understanding of constituent contributions to food characteristics. Therefore, the influences of microbes and their products such as lactic acid, acetic acid, and ethanol on aroma profiles were investigated using gas chromatography/mass spectrometry (GC/MS)-based metabolic profiling. The presence of aroma constituents influenced by microbes and chemically influenced by lactic acid, acetic acid, and ethanol were proposed. Most of the aroma constituents were not produced by adding ethanol alone, confirming the participation of yeast in aroma production. It was suggested that lactic acid bacterium relates to a key aromatic compound, 2,5-dimethyl-4-hydroxy-3(2H)-furanone. However, most of the measured aroma constituents changed similarly in both samples with lactic acid bacterium and acids. Thus, it was clear that the effect of lactic acid and acetic acid on the aroma profile was significant.

A comparative secretome analysis of industrial Aspergillus oryzae and its spontaneous mutant ZJGS-LZ-21

Aspergillus oryzae koji plays a crucial role in fermented food products due to the hydrolytic activities of secreted enzymes. In the present study, we performed a comparative secretome analysis of the industrial strain of Aspergillus oryzae 3.042 and its spontaneous mutantZJGS-LZ-21. One hundred and fifty two (152) differential protein spots were excised (p<0.05), and 25 proteins were identified. Of the identified proteins, 91.3% belonged to hydrolytic enzymes acting on carbohydrates or proteins. Consistent with their enzyme activities, the expression of 14 proteins involved in the degradation of cellulose, hemicellulose, starch and proteins, increased in the ZJGS-LZ-21isolate. In particular, increased levels of acid protease (Pep) may favor the degradation of soy proteins in acidic environments and promote the cleavage of allergenic soybean proteins in fermentation, resulting in improvements of product safety and quality. The ZJGS-LZ-21 isolate showed higher protein secretion and increased hydrolytic activities than did strain 3.042, indicating its promising application in soybean paste fermentation.

Comparative study on fermentation performance in the genome shuffled Candida versatilis and wild-type salt tolerant yeast strain

BACKGROUND

The fermentation performance of a genome-shuffled strain of Candida versatilis S3-5, isolated for improved tolerance to salt, and wild-type (WT) strain were analysed. The fermentation parameters, such as growth, reducing sugar, ethanol, organic acids and volatile compounds, were detected during soy sauce fermentation process.

RESULTS

The results showed that ethanol produced by the genome shuffled strain S3-5 was increasing at a faster rate and to a greater extent than WT. At the end of the fermentation, malic acid, citric acid and succinic acid formed in tricarboxylic acid cycle after S3-5 treatment elevated by 39.20%, 6.85% and 17.09% compared to WT, respectively. Moreover, flavour compounds such as phenethyl acetate, ethyl vanillate, ethyl acetate, isoamyl acetate, ethyl myristate, ethyl pentadecanoate, ethyl palmitate and phenylacetaldehyde produced by S3-5 were 2.26, 2.12, 2.87, 34.41, 6.32, 13.64, 2.23 and 78.85 times as compared to WT.

CONCLUSIONS

S3-5 exhibited enhanced metabolic ability as compared to the wild-type strain, improved conversion of sugars to ethanol, metabolism of organic acid and formation of volatile compounds, especially esters, Moreover, S3-5 might be an ester-flavour type salt-tolerant yeast. © 2016 Society of Chemical Industry.

Evaluation of commercial soy sauce koji strains of Aspergillus oryzae for γ-aminobutyric acid (GABA) production

In this study, four selected commercial strains of Aspergillus oryzae were collected from soy sauce koji. These A. oryzae strains designated as NSK, NSZ, NSJ and NST shared similar morphological characteristics with the reference strain (A. oryzae FRR 1675) which confirmed them as A. oryzae species. They were further evaluated for their ability to produce γ-aminobutyric acid (GABA) by cultivating the spore suspension in a broth medium containing 0.4 % (w/v) of glutamic acid as a substrate for GABA production. The results showed that these strains were capable of producing GABA; however, the concentrations differed significantly (P < 0.05) among themselves. Based on the A. oryzae strains, highest GABA concentration was obtained from NSK (194 mg/L) followed by NSZ (63 mg/L), NSJ (51.53 mg/L) and NST (31.66 mg/L). Therefore, A. oryzae NSK was characterized and the sequence was found to be similar to A. oryzae and A. flavus with 99 % similarity. The evolutionary distance (K nuc) between sequences of identical fungal species was calculated and a phylogenetic tree prepared from the K nuc data showed that the isolate belonged to the A. oryzae species. This finding may allow the development of GABA-rich ingredients using A. oryzae NSK as a starter culture for soy sauce production.

Two genomes are better than one: history, genetics, and biotechnological applications of fungal heterokaryons

Heterokaryosis is an integral part of the parasexual cycle used by predominantly asexual fungi to introduce and maintain genetic variation in populations. Research into fungal heterokaryons began in 1912 and continues to the present day. Heterokaryosis may play a role in the ability of fungi to respond to their environment, including the adaptation of arbuscular mycorrhizal fungi to different plant hosts. The parasexual cycle has enabled advances in fungal genetics, including gene mapping and tests of complementation, dominance, and vegetative compatibility in predominantly asexual fungi. Knowledge of vegetative compatibility groups has facilitated population genetic studies and enabled the design of innovative methods of biocontrol. The vegetative incompatibility response has the potential to be used as a model system to study biological aspects of some human diseases, including neurodegenerative diseases and cancer. By combining distinct traits through the formation of artificial heterokaryons, fungal strains with superior properties for antibiotic and enzyme production, fermentation, biocontrol, and bioremediation have been produced. Future biotechnological applications may include site-specific biocontrol or bioremediation and the production of novel pharmaceuticals.

Increasing Protease Activities and Antioxidant Properties of Koji for Soy Sauce Brewing by Adding a Medicinal Herb Rhodiola rosea

Koji preparation is the key step in soy sauce brewing. In this study, 21 medicinal herbs were tested for their abilities in enhancing the protease activities of soy sauce koji. Among these herbs Rhodiola rosea was found to be the most efficient in increasing protease activities. Kinetic analyses revealed that R. rosea addition not only promoted microbe growth and increase the activities of neutral and acid proteases (by 29.8% and 13.4%, respectively) but also elevated α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging activity and total phenolics and flavonoids (by 9.5%, 47.1% and 14.1%, respectively); the formations of proteases and antioxidant properties depend largely on microbe growth; and the promotion effects of R. rosea addition were mainly displayed in later stage of fermentation. Using the R. rosea koji for soy sauce production resulted in 8.9%, 19.1%, 6.6%, 23% and 102% higher of total and amino-type nitrogen contents, protein utilization, total phenolics and flavonoids, respectively.

Streptomycin resistance-aided genome shuffling to improve doramectin productivity of Streptomyces avermitilis NEAU1069

Genome shuffling is an efficient approach for the rapid engineering of microbial strains with desirable industrial phenotypes. In this study, a strategy of incorporating streptomycin resistance screening into genome shuffling (GS-SR) was applied for rapid improvement of doramectin production by Streptomyces avermitilis NEAU1069. The starting mutant population was generated through treatment of the spores with N-methyl-N’-nitro-N-nitrosoguanidine and ultraviolet (UV) irradiation, respectively, and five mutants with higher productivity of doramectin were selected as starting strains for GS-SR. Finally, a genetically stable strain F4-137 was obtained and characterized to be able to yield 992 ± 4.4 mg/l doramectin in a shake flask, which was 7.3-fold and 11.2-fold higher than that of the starting strain UV-45 and initial strain NEAU1069, respectively. The doramectin yield by F4-137 in a 50-l fermentor reached 930.3 ± 3.8 mg/l. Furthermore, the factors associated with the improved doramectin yield were investigated and the results suggested that mutations in ribosomal protein S12 and the enhanced production of cyclohexanecarboxylic coenzyme A may contribute to the improved performance of the shuffled strains. The random amplified polymorphic DNA analysis showed a genetic diversity among the shuffled strains, which confirmed the occurrence of genome shuffling. In conclusion, our results demonstrated that GS-SR is a powerful method for enhancing the production of secondary metabolites in Streptomyces.

Characterisation of acid proteases from a fusant F76 and its progenitors Aspergillus oryzae HN3042 and Aspergillus niger CICC2377

The characteristics of a novel acid protease from a fusant F76 were comparatively evaluated with those from its progenitors Aspergillus oryzae HN3042 and A. niger CICC2377. The UV spectra of these three acid proteases were similar, but fluorescence spectra were different. The acid protease from F76 contained 7.1% α‐helix, 39.4% β‐sheet, 24.7% β‐turn and 32% aperiodic coil, unlike those from its progenitors. The acid protease from F76 was active in the temperature range of 35–55 °C with the optimum temperature of 40 °C and was stable in the pH range of 2.5–6.5 with the optimum pH of 3.5, while those values from A. oryzae HN3042 and A. niger CICC2377 were 45 °C, 4.0 and 40 °C, 3.5, respectively. The kinetic parameters of the acid protease from F76 were different from its progenitors and the Michaelis constant, maximum velocity, activation energy, and attenuation index were 0.96 mg mL−1, 135.14 μmol min−1 mg−1, 64.11 kJ mol−1 and 0.59, respectively.