Bacillus fermentation of soybeans

Partial purification and characterization of protease extracted from kinema

Proteases are large group of highly demanded enzymes having huge application in food and pharmaceutical industries. Numerous sources, including plants, microorganisms, and animals, can be used to obtain protease. Due to its affordability and safety consideration, fermented foods have recently attracted more attention as a source of microbial protease. The present study aimed to extract protease from kinema, partially purify the extracted protease following dialysis after precipitation with ammonium sulfate, and determine general characteristics of protease. The kinema having highest proteolysis activity after three days of control fermentation (Temperature 30±2 °C, RH 66 ± 2%) was taken for the study. About 2.45 fold of purification with overall recovery of 63.21% was achieved after precipitation with ammonium sulfate at 30-70% saturation level followed by dialysis of crude extracted protease. The dialysed kinema protease had specific activity of 7.90 U/mg. The enzyme remained actively functional across a wider pH (5-9) and temperature (40-60 °C) range. SDS-PAGE and Zymogram confirmed the presence of three major active bands respectively of 29.04 kDa, 36.09 kDa and 46.35 kDa in the kinema protease extract. The enzyme kinetics data on casein, fitted to Mechaelis Mentens' plots showed the protease had Vmax of 1.001 U/ml with corresponding Km value of 0.825 mg/ml. Metal ions such as iron, mercury and aluminium showed the inhibition effect whereas presence of sodium, zinc, and calcium shows the activation effect on protease performance. The enzyme was active over various natural substrates; showing maximal activity on casein, and subsequent to bovine serum albumin, gelatin, hemoglobin and whey protein respectively. Furthermore, molecular weight distribution of the protease extract and activity inhibition with ethylenediaminetetraacetic acid and phenylmethylsulfonyl fluoride, suggesting the protease from kinema could be a metal dependent serine protease or mixture of them.

Soybean fermentation: Microbial ecology and starter culture technology

Fermented soybean products, including Soya sauce, Tempeh, Miso, and Natto have been consumed for decades, mainly in Asian countries. Beans are processed using either solid-state fermentation, submerged fermentation, or a sequential of both methods. Traditional ways are still used to conduct the fermentation processes, which, depending on the fermented products, might take a few days or even years to complete. Diverse microorganisms were detected during fermentation in various processes with Bacillus species or filamentous fungi being the two main dominant functional groups. Microbial activities were essential to increase the bean's digestibility, nutritional value, and sensory quality, as well as lower its antinutritive factors. The scientific understanding of fermentation microbial communities, their enzymes, and their metabolic activities, however, still requires further development. The use of a starter culture is crucial, to control the fermentation process and ensure product consistency. A broad understanding of the spontaneous fermentation ecology, biochemistry, and the current starter culture technology is essential to facilitate further improvement and meet the needs of the current extending and sustainable economy. This review covers what is currently known about these aspects and reveals the limited available information, along with the possible directions for future starter culture design in soybean fermentation.

Physical, chemical and adsorption isotherm characteristics of fermented soybean cultivars, and cracked and dehulled African locust bean using selected Bacillus spp

Physical, chemical and adsorption isotherm characteristics of fermented soybean cultivars and dehulled African locust bean using selected Bacillus spp. were investigated. The CIE Lab, pH, titratable acidity, temperature and viable cells of the fermented cotyledons count increased significantly (p < 0.05) during the 5 days fermentation period. The CIE (Lab) varied with method of dehulling of cotyledons prior to and during fermentation, drying and milling. Protein content of African locust bean (25.50-40.25%) and soybean (40.15-50.60%) increased, but carbohydrate content reduced during fermentation of African locust bean (30.20-15.08%) and soybeans (18.21-12.08%). Adsorption isotherm patterns of the dried and milled African locust bean and soybean cultivars were sigmoidal. Of the eight models used, the BET and GAB models gave good fit, with a good correlation coefficient (0.95-0.76) and low average (81.93-14.82). The GAB had better fit, greater relevance and theoretical significance when compared with other models. Cracking to remove cotyledons from locust beans prior to fermentation yielded condiment with better aesthetic appeal and nutritional qualities than the traditional cooking for extensive period used for dehulling and softening of African locust bean seeds.

Bacterial and Fungal Microbiota Associated with the Ensiling of Wet Soybean Curd Residue under Prompt and Delayed Sealing Conditions

Wet soybean curd residue (SCR) obtained from two tofu factories (F1 and F2) was anaerobically stored with or without added beet pulp (BP). Sealing was performed on the day of tofu production (prompt sealing (PS)) or 2 days after SCR was piled and unprocessed (delayed sealing (DS)). Predominant lactic acid fermentation was observed regardless of the sealing time and BP addition. Acinetobacter spp. were the most abundant (>67%) bacteria in pre-ensiled SCR, regardless of the factory and sealing time. In PS silage, the abundances of typical lactic acid-producing bacteria, such as Lactobacillus, Pediococcus, and Streptococcus spp. reached >50%. In DS silage, Acinetobacter spp. were the most abundant in F1 products, whereas Bacillus spp. were the most abundant in long-stored F2 products. The fungal microbiota were highly diverse. Although Candida, Aspergillus, Cladosporium, Hannaella, and Wallemia spp. were found to be the most abundant fungal microbiota, no specific genera were associated with factory, sealing time, or fermentation products. These results indicated that owing to preceding processing, including heating, distinctive microbiota may have participated in the ensiling of wet by-products. Lactic acid fermentation was observed even in DS silage, and an association of Bacillus spp. was suggested.

Fermentation of texturized vegetable proteins extruded at different moisture contents: effect on physicochemical, structural, and microbial properties

To investigate the effect of fermentation on texturized vegetable protein (TVP), TVPs extruded at 40 and 50% feed moisture contents (MC) were fermented using Bacillus subtilis at 37 °C. Physicochemical, structural and microbial properties of TVPs were determined at 0, 12, 24, 36, 48, and 60 h after fermentation. Integrity index of fermented TVPs did not change significantly until 24-36 h after fermentation. Springiness and cohesiveness remained stable after fermentation in all samples. Significant total color change was observed during fermentation. The pH values dropped initially and rose again with a coincident increase in nitrogen solubility index and viable cell count of B. subtilis. During fermentation, TVP extruded at 50% MC maintained higher chewiness, hardness, integrity index, and layered structure than that extruded at 40% MC. The study demonstrated that fermenting the TVP extruded at 50% MC has potential to produce a new type of TVP based B. subtilis fermented food.

The effect of aeration and mixing in developing a dairy-based functional food rich in menaquinone-7

Vitamin menaquinone-7 (MK-7) supplementation improves bone health and reduces the incidence of osteoporosis. Despite the recent developments in MK-7 fermentation using Bacillus subtilis natto, low fermentation yields, as well as complicated downstream processing steps, are still the main reasons for the expensive final product. To overcome these issues, developing a fermented dairy-based product rich in MK-7 by avoiding costly downstream steps and optimising the fermentation operating conditions to enhance the MK-7 concentration would be an alternative approach. The present study, therefore, aims to evaluate the role of agitation and aeration as the key operating conditions on MK-7 production by Bacillus subtilis natto using a milk media. The agitation and aeration rates of 525 RPM and 5 VVM were found to be the optimum levels leading to the production of 3.54 mg/L of MK-7. Further, the sensory evaluation was performed to compare the sensory properties of the freeze-dried fermented samples with non-fermented milk samples. The results illustrated that the fermented samples had a significant saltiness with intense aroma resulting in the less acceptability of them by the panellists.

Microbiology of Ethiopian Traditionally Fermented Beverages and Condiments

Globally, fermented beverage and condiments are made by using different conventional practices, raw materials, and microorganisms. This paper presents the available literature review on the technology and microbiology of traditional Ethiopian beverages and condiment products. Traditional fermented beverage and condiment products have essential vitamins, minerals, enzymes, and antioxidants that are all enhanced through the process of traditional fermentation practices. In Ethiopia, fermented beverage and condiment products have practiced in a long history. During the production of traditional fermented beverage and condiment products, controlled natural fermentation process with the absence of starter cultures are used to initiate it. Moreover, the preparation of many traditionally fermented beverage and condiment products is still practiced in a household art, thereby a wide variety of fermented beverages and condiments are consumed in Ethiopia. In conclusion, the review discusses the nature of the beverage and condiment preparation, poor traditional household processing, and the extent and limitation of scientific work done so far and suggests some recommendations to limit the problem in Ethiopia.

Promotion of lipopeptide antibiotic production by Bacillus sp. IA in the presence of rice husk biochar

The purpose of this study is to isolate the beneficial microorganisms whose growth is promoted in the presence of charcoal materials. We successfully isolated strain IA, whose growth is promoted on an agar plate with charcoal materials, and identified it as a novel strain of the Bacillus sp. The growth of strain IA in the liquid medium was promoted by the addition of both activated charcoal (AC) and rice husk biochar (RHB). Moreover, the sporulation of strain IA in the RHB medium and the antifungal activity of the culture supernatant of the RHB medium were much higher than those with AC. HPLC and MS analyses revealed that strain IA produced an antifungal lipopeptide iturin A, and the yield of iturin A in the RHB medium was 8 times higher than that in the medium without RHB. This is the first paper to describe the positive effect of RHB on microbial metabolisms.

Development of lotus root fermented sugar syrup as a functional food supplement/condiment and evaluation of its physicochemical, nutritional and microbiological properties

Lotus (Nelumbo nucifera) root has been used as an edible vegetable in East Asia for thousands of years. The present research was aimed to explore the physicochemical, nutritional and microbiological safety of lotus root fermented sugar syrup as a fermented food supplement or condiment for human health benefits. In this study, the physicochemical, nutritional and microbiological safety properties of lotus root syrup fermented with 57° Brix brown sugar at different time periods until 6 months (180 days) was investigated. There was a significant improvement as compared to 57° Brix brown sugar broth (as a control) in the total acceptability and physicochemical properties of lotus root sugar syrup samples such as pH and color improvement. The red color values of 180 days lotus root fermented sugar syrup samples were significantly enhanced (6.85 ± 0.58) when compared with the control (0.20 ± 0.15). In addition, the total protein content was increased from 8.27 ± 0.86 to 392.33 ± 7.19 μg/mL, along with the increase in fermentation time reaching to the level of consumption acceptability. All the lotus root fermented sugar syrup samples were subjected to microbiological analysis. It was found that the coliform, Bacillus cereus, Escherichia coli, Salmonella and Staphylococcus aureus counts were not detected in majority of the samples, confirming the high degree of hygiene processing of lotus root fermented sugar syrup samples for its use as a food supplement or condiment.

Molecular analysis of bacterial community dynamics during the fermentation of soy-daddawa condiment

Bacterial community dynamics during soy-daddawa fermentation was investigated using culture-dependent and PCR-denaturing gradient gel electrophoresis (PCR-DGGE) molecular methods. The total titratable acidity (TTA), pH, and bacterial counts (BCs) were monitored daily during a 72-h fermentation period. Bacteria were characterized based on 16S rRNA gene sequencing. TTA ranged from 0.08 to 0.26 mg lactic acid/g, whereas pH ranged from 7.01 to 8.19. BCs increased from 3.9 to 10.61 log CFU/g. Fifty-eight isolates were obtained by culture method and clustered into seven operational taxonomic units (OTUs) at 97% sequence similarity, whereas four OTUs were obtained from the PCR-DGGE method. Taxonomic identification revealed that bacteria belonged to the genera Bacillus, Enterobacter, Enterococcus, and Staphylococcus with B. subtilis being present throughout fermentation. Medically significant isolates, including B. anthracis, Enterococcus casseliflavus, and Enterobacter hormaechei were detected. These results emphasize the need for starter culture utilization and offer a platform for starter culture screening and selection.

Optimization of soybean processing into kinema, a Bacillus-fermented alkaline food, with respect to a minimum level of antinutrients

AIMS

Optimization of traditional processing of soybeans using response surface methodology (RSM) to achieve a minimum level of antinutritional factors (ANFs) in kinema.

METHODS AND RESULTS

Central composite rotatable designs were used to optimize the processing stages of kinema preparation. In each stage, the linear or quadratic effects of independent variables were significant in minimizing ANF levels. The predicted optimum condition for soaking was when the raw beans-water ratio was 1 : 10, and the soaking temperature, time and pH were 10°C, 20 h and 8·0 respectively. Here, tannins content (TC), phytic acid content (PAC) and trypsin inhibitor activity (TIA) decreased (P < 0·05). While haemagglutinating activity (HA) level remained unchanged (P < 0·05), total biogenic amines content (TBAC) increased. The optimum condition for cooking was optimally soaked beans-water ratio of 1 : 5, and cooking pressure and time were 1·10 kg cm(-2) and 20 min respectively. Here, TC, PAC, TIA and HA decreased (P < 0·05), but TBAC remained unchanged compared to optimally soaked beans. TC and HA went below the level of detection. The optimum condition for fermentation was obtained when inoculum load was 10(3) total cells g(-1) grits, and fermentation temperature and time were 37°C and 48 h respectively. Fermentation of optimally cooked beans caused a reduction (P < 0·05) of PAC. While TIA remained unchanged (P < 0·05), TBAC increased. In kinema, TC, PAC, TIA and HA decreased (P < 0·05) over raw beans by 100, 61, 71 and 100% respectively. Good agreement was observed between predicted values and experimental values.

CONCLUSIONS

The processing treatments significantly minimized the level of ANFs in soybeans.

SIGNIFICANCE AND IMPACT OF THE STUDY

RSM was successfully deployed to obtain the optimum condition for kinema-making with a minimum level of ANFs without impairing sensory attributes of the product. The results are useful for commercial production of kinema.

Antioxidant and antihypertensive properties of liquid and solid state fermented lentils

The effect of liquid (LSF) and solid state fermentation (SSF) of lentils for production of water-soluble fractions with antioxidant and antihypertensive properties was studied. LSF was performed either spontaneously (NF) or by Lactobacillus plantarum (LP) while SSF was performed by Bacillus subtilis (BS). Native lactic flora in NF adapted better than L. plantarum to fermentative broth and BS counts increased 4.0 logCFU/g up to 48 h of SSF. LSF water-soluble fractions had higher (P ≤ 0.05) free amino groups, GABA content, antioxidant and angiotensin I-converting enzyme inhibitory (ACEI) activities than SSF. In addition, GABA and ACEI activity of LSF increased in a time-dependent manner. Proteolysis by BS was limited, with slight changes in free amino groups, while GABA, total phenolic compounds and antioxidant capacity increased throughout fermentation. Higher antihypertensive potential was observed in NF (96 h) characterised by the highest GABA content (10.42 mg/g extract), ACE-inhibitory potency (expressed as IC(50)) of 0.18 mg protein/ml and antioxidant capacity of 0.26 mmol Trolox equivalents/g extract. Therefore, water-soluble fermented lentil extracts obtained by LSF are particularly promising as functional ingredients in preventing hypertension.

Study on the production of chitin and chitosan from shrimp shell by using Bacillus subtilis fermentation

Fermentation of shrimp shell in jaggery broth using Bacillus subtilis for the production of chitin and chitosan was investigated. It was found that B. subtilis produced sufficient quantities of acid to remove the minerals from the shell and to prevent spoilage organisms. The protease enzyme in Bacillus species was responsible for the deprotenisation of the shell. The pH, proteolytic activity, extent of demineralization and deprotenisation were studied during fermentation. About 84% of the protein and 72% of the minerals were removed from the shrimp shell after fermentation. Mild acid and alkali treatments were given to produce characteristic chitin and their concentrations were standardized. Chitin was converted to chitosan by N-deacetylation and the properties of chitin and chitosan were studied. FTIR spectral analysis of chitin and chitosan prepared by the process was carried out and compared with spectra of commercially available samples.

Flavouring composition prepared by fermentation with Bacillus spp

Fermented foodstuffs and condiments remain a key constituents of diets throughout many parts of Asia and Africa. In cases where the process of fermentation evolved for the development of taste or aroma, it often resulted in enhanced nutrition, stabilisation of the original raw materials, and detoxification of anti-nutrient factors. Several fermented products rely on the participation of various Bacillus species, including Bacillus natto and B. subtilis. Often, the finished products are of a very local character and exhibit sensory properties resulting from unique flora and processing technologies applied in small scale, home-based fermentations. Fermentation with B. natto and B. subtilis can produce very characteristic aromas in fermented products such as natto and dawadawa (also referred to as daddawa). Moreover, the hydrolytic capabilities of these microorganisms can result in a precursor-rich environment, which is useful for subsequent reactions leading to flavour production. A 1995 patented process demonstrated the ability to produce a fermented flavouring composition with the use of Bacillus spp. Hydrolysed protein obtained after fermentation with Bacillus spp. is mixed with reactive flavour precursors, which are subsequently heated to induce flavour formation and can be dried to a powder format. The product of this patented process imparts a basic meaty flavour, with a reduced yet characteristic dawadawa-like aroma. This paper briefly summarises some of the characteristics and uses of traditional dawadawa and illustrates alternatives described in the patent for the production of a process flavour base. Issues and considerations for the industrialisation of a fermentation process are briefly discussed, as well as some future opportunities for development and exploitation of traditional fermentation technology.

In vitro digestibility of bacillus fermented soya bean

Bacillus fermented legume products include among others dawadawa and soumbala made from African locust bean, and natto and kinema made from soya bean. Bacillus subtilis is the dominant species involved in the fermentation. During Bacillus fermentation for 48 h of autoclaved soya bean the quantity of soluble and dialyzable matter increased from 22% and 6% up to 65% and 40%, respectively. Protein and carbohydrate degradation during fermentation of soya bean with several Bacillus spp. was investigated and appeared to be substantial during the first 18 h of fermentation resulting in the release of high levels of peptides and oligosaccharides. In vitro digestibility was increased from 29% up to 33-43% after Bacillus fermentation for 48 h. It was shown that Bacillus spp. were able to degrade soya bean macromolecules to a large extent resulting in water-soluble low molecular weight compounds. In vitro digestion of Bacillus fermented soya bean using gastrointestinal enzymes only slightly increased the amount of dialyzable matter, which clearly demonstrated the beneficial effect of Bacillus fermentation on food nutrient availability.

Effect of ammonia on the growth of Bacillus species and some other bacteria

The tolerance of 26 Bacillus species isolated from alkaline fermented foods, five other bacilli and nine non spore-forming bacteria to alkaline pH and ammonia was determined. All grew at pH 7, 8 and 9 in the presence of 930 mmol l-1 NH4 + at pH 7.0, and in the presence of NH3 concentrations up to 5 mmol l-1 at pH 7.0 and 8.0. At higher NH3 concentrations, growth of some of the bacteria was inhibited and at 500 mmol l-1 only B. pasteurii and B. pumilus grew. Bacteria from alkaline food fermentations included strains relatively sensitive to NH3 (inhibited by 50 mmol l-1) and relatively tolerant strains (grew in the presence of 300 mmol l-1) and there was no evidence that they were more tolerant to NH3 than bacteria not associated with these fermentations.

Control of ammonia formation during Bacillus subtilis fermentation of legumes

The control of ammonia formation during the Bacillus subtilis fermentation of autoclaved, roasted soybean cotyledons (Glycine max) and of autoclaved African locust bean cotyledons (Parkia spp.) was investigated. Addition of NaCl, 1.5 mol (kg wet cotyledons)-1, part way through the fermentation inhibited ammonia formation and softening of the cotyledons. Addition of glycerol, 1.7 mol (kg wet cotyledons)-1 part way through the fermentation inhibited alkalinisation and ammonia formation while allowing enzymic activity and softening of the cotyledons to continue. Restriction of the oxygen supply by incubating the cotyledons in a sealed container also prevented excessive ammonia production and increase in pH value. Fermentations conducted in sealed containers with an air to cotyledons ratio of approximately 130-175 ml air (g wet cotyledons)-1 supported good microbial growth and proteolysis without the formation of detectable ammonia aroma.

Alkaline-fermented foods: a review with emphasis on pidan fermentation

Alkaline-fermented foods constitute a group of less-known food products that are widely consumed in Southeast Asia and African countries. They can be made from different raw ingredients. For instance, Japanese natto, Thai thua-nao, and kinema are made from cooked soybeans, dawadawa from African locust beans, ogiri from melon seeds, ugba from African oil beans, kawal from fresh legale leaves, owoh from cotton seeds, and pidan from fresh poultry eggs. In alkaline-fermented foods, the protein of the raw materials is broken down into amino acids and peptides; ammonia is released during the fermentation, raising the pH of the final products and giving the food a strong ammoniacal smell. Most alkaline fermentations are achieved spontaneously by mixed bacteria cultures, principally dominated by Bacillus subtilis. In other cases, pure cultures can be used. For example, Japanese natto is inoculated with a pure culture of B. subtilis var natto. Pidan is a special example of alkaline fermentation. Instead of using microorganisms, pidan is made using an alkali-treated fermentation. Sodium hydroxide (NaOH) is produced from the reaction of sodium carbonate (Na2CO3), water (H2O), and calcium oxide (CaO) of pickle or coating mud. NaOH penetrates into the eggs, causing the physicochemical changes, color changes, and gelation. The appearance of pidan differs from fresh eggs in that the white becomes a semitransparent tea-brown color, and the yolk is solid or semisolid with a dark-green color. The nutritional value of pidan is slightly decreased compared with fresh eggs, but pidan has an extremely long shelf life and a pleasant, fragrant taste that is preferred by most people in Southeast Asian countries. In a small-scale laboratory study conducted by the authors, B. subtilis was not found in pidan. Four Staphylococcus spp. (S. cohnii, S. epidermidis, S. haemolyticus, and S. warneri) and two strains of Bacillus spp. (B. cereus and B. macerans) were isolated from pidan. Staphylococcus spp. did not contribute to the fermentation and were considered contaminants.

Fungal interactions in food fermentations

Fermented foods are of importance worldwide. Most are prepared under nonsterile conditions using mixed cultures, either deliberately or unavoidably. Fungal mixed cultures show interactive relations at various levels. In this paper, inhibitory effects among fungi owing to competition, formation of organic acids, toxic proteins, and mycotoxins are discussed. In addition, fungi show inhibitory effects towards bacteria and vice versa, through pH changes, and excretion of organic acids, antibiotics, peptides, etc. Stimulatory interactions among fungi and between fungi and bacteria relate mainly to carbon and nitrogen metabolism, and they play an important role in the inherent stability of mixed-culture systems maintained by enrichment techniques. Better understanding of natural mixed-culture fermentations has evolved into the development of the concept of cocultivation employing compatible microbial strains of complementary metabolic ability. Especially in the area of direct conversion of complex carbohydrates (e.g., starch, inulin, or lignocellulosic matter into ethanol), cocultivation has much to offer. Genetic modification of starter organisms offers opportunities to improve, for example, their ability to degrade substrate with a minimum of catabolite repression, and produce final products of superior quality. This is illustrated by recent recombinant DNA constructs for alcoholic fermentations. Key words: food, fungi, interaction, inhibition, stimulation, cocultivation.