Anaerobic Solid-state Fermentation Research Articles

Anaerobic solid-state fermentation with Bacillus subtilis for digesting free gossypol and improving nutritional quality in cottonseed meal.

Microbial fermentation is an effective method to degrade free-gossypol, which is a toxic substance restricting the utilization of cottonseed meal in animal husbandry. However, there are few researches on the nutritional effect and the change of bacterial community on cottonseed meal fermented with anaerobic solid-state fermentation. This study evaluated the effects of fermentation with Bacillus sp. on gossypol degradation and nutritional quality improvement in cottonseed meal (CM), as well as the changes of bacterial community structure during fermentation. The strains with high activity for digesting free gossypol were screened from high protease-producing strains preserved in the laboratory. Then the strains which had both the gossypol degradation activity and protease producing activity were selected to degrade macromolecular protein and free gossypol in CM. The unsterilized SSF medium was inoculated with 109 CFU/kg Bacillus culture and fermented at room temperature for 14 days. Each group had three parallels. And the effects of anaerobic solid-state fermentation on unsterilized CM was evaluated. Results showed that for the seven strains with high activity for digesting free gossypol and producing protease that were screened, free gossypol content in fermented cottonseed meal (FCM) decreased and acid-soluble protein (ASP) contents increased. Among them, strain M-15 had the best fermentation effect, with the free gossypol degradation rate of 93.46% and acid soluble protein content of 13.26%. M-15 was identified as Bacillus subtilis. During fermentation with M-15, the bacterial diversity in CM was reduced, but not significant and the community structure was simpler significantly. The strain M-15 selected in this experiment reduced the free gossypol content and improved the nutritional quality of CM through anaerobic solid-state fermentation, which can be used for industrial large-scale production.

Effect of Solid-State Fermentation on Vitamin C, Photosynthetic Pigments and Sugars in Willow Herb (Chamerion angustifolium (L.) Holub) Leaves.

The goal of this investigation was to establish the impact of solid-state fermentation of different durations on the quantitative changes of vitamin C, sugars and photosynthetic pigments in the leaves of willow herbs. The tested leaves were fermented using two solid-state fermentation methods (aerobic and anaerobic) for different time periods (unfermented and fermented for 24, 48 and 72 h). The quantitative and qualitative composition of chlorophylls, carotenoids, sugars and vitamin C were determined using high performance liquid chromatography (HPLC) with UV detectors. Results indicated that aerobic and anaerobic solid-state fermentation significantly decreased the contents of vitamin C, dehydroascorbic and L-ascorbic acids in leaves compared with the unfermented leaves. The contents of total chlorophyll and chlorophyll a were the highest in unfermented leaves and after 24 h of aerobic solid-state fermentation. The maximum content of total carotenoids in leaves were after 48 and 72 h of aerobic solid-state fermentation (149.31 mg 100 g-1 and 151.51 mg 100 g-1, respectively). The application of anaerobic solid-state fermentation resulted in significant increase in the content of total sugars, fructose and glucose in investigated samples. In conclusion, optimization of fermentation parameters allows increasing the content of sugars and photosynthetic pigments in leaves of willow herbs.

Anaerobic Solid-State Fermentation of Soybean Meal With Bacillus sp. to Improve Nutritional Quality.

The study evaluated the impact of fermentation with Bacillus sp. on the nutritional quality of soybean meal (SBM) and the changes of bacterial community structure during fermentation. High protease-producing strains were screened to degrade SBM macromolecular protein and anti-nutritional factors (ANFs). Unsterilized SBM then underwent an anaerobic solid-state fermentation method to evaluate the effects of fermentation. Results showed that for the nine high-producing protease strains that were screened, acid-soluble protein (ASP) contents in fermented SBM increased, with the highest value found to be 13.48%, which was fermented using strain N-11. N-11 was identified as Bacillus subtilis. N-11 fermentation reduced ANFs such as glycinin and β-conglycinin by 82.38 and 88.32%, respectively. During N-11 fermentation, the bacterial richness and diversity in SBM increased but not significantly. The high-yield protease strain B. subtilis N-11 selected in this experiment improved the nutritional quality of SBM through fermentation, and it can be used for industrial large-scale production.

Polyphenols, Antioxidant Activity and Volatile Compounds in Fermented Leaves of Medicinal Plant Rosebay Willowherb (Chamerion angustifolium (L.) Holub).

At present, the consumption of medical plants and functional foods is growing in the whole world. Rosebay willowherb (Chamerion angustifolium (L.) Holub) is an important medicinal plant that has various pharmacological effects (antioxidant, anti-inflammatory, anticancer, and others), can improve the state of health and well-being, and reduce the risk of various diseases. The aim of this work was to investigate volatile compounds, polyphenols, and antioxidant activity in rosebay willowherb leaves fermented for 24 and 48 h in solid state fermentation under aerobic and anaerobic conditions. High-performance liquid chromatography (HPLC) for polyphenols and the spectrophotometric method for antioxidant activity determinations were used. To recognize and identify the leaves’ fragrances, electronic nose (Alpha M.O.S) measurement technology was used. The results showed that the highest amounts of total polyphenols in dried matter were after 48 h aerobic solid state fermentation (SSF). Antioxidant activity was higher under 48 h SSF compared to the control. The most abundant flavoring compound groups were esters, terpenes, and aldehydes. In unfermented leaves, (z)-3-hexen-1-ol, acetate, hexyl acetate, and trans-hex-2-enyl acetate prevailed, characterized by fragrances of greenery, flowers, and fruits. The undesired esters group compounds, ethyl butyrate and butyl acetate, with pungent odor, were detected after 48 h anaerobic SSF.

Enhanced stepwise spraying effects on gas production by anaerobic solid-state fermentation in a high-density straw bed

Rice straw bales and fresh pig manure were used as feedstock, and added microbial fortification agent and stepwise spraying methods were used to investigate the effect on the gas yield characteristics and fermentation properties of garage-type anaerobic solid-state fermentation at ambient temperature. The test results showed that the added microbial fortification agent advanced the arrival time of the peak temperature by one day and increased the average fermentation temperature by 8.28%. The microbial fortification agent can increase gas production and the time of first yield peak and shorten the start-up time. The maximum gas yield of the enhanced groups was 13.01% higher than the ordinary groups, and the methane concentration increased 16.98%. After the second gas yield peak, the reduction of spraying frequency had almost no effect on the gas yield. The stepwise spraying method was helpful to improve the moisture distribution and the degradation rate of the middle layer. This study provides a basis for evaluating and improving the operating efficiency of the anaerobic solid-state fermentation systems.

Modeling of industrial-scale anaerobic solid-state fermentation for Chinese liquor production

Traditional solid-state fermentation processes can give fluctuating product quality and quantity due to difficulties in control and scale up. This paper describes an engineering study of an industrial-scale anaerobic solid-state fermentation process for Chinese liquor (Baijiu) production, aimed at better understanding of the traditional process, as an initial step for future optimization. This mixed-culture fermentation is done in 0.44-m3 vessels embedded in the soil. At this scale, the fermentation is limited by product inhibition. We developed mathematical models based on the Han-Levenspiel equation for product inhibition, with parameters derived from measured data. The models accurately predicted the concentrations of starch and dry matter. A model with radial conduction into a small soil volume around the fermenter and consecutive vertical conduction into the underlying soil accurately predicted the pit temperature in the heating and cooling phases. This model is very sensitive to the values used for the enthalpies of combustion, meaning that direct measurement of the heat production rate would be preferable. In the industry practice, the fermenter volume can be from around 0.20 to 15.00 m3. The model predicts that overheating will occur not only in larger fermenters, but also in the 0.44-m3 fermenters when the soil temperature is high in summer. Our model predictions are consistent with observed behavior in the industry. Our findings can be used to improve this traditional process, as well as similar systems.

Metabolism analysis for enhanced nutritional profile of chestnuts subjected to anerobic solid‐state fermentation by probiotic lactic acid bacteria

The improved nutritional composition of anaerobic solid-state fermentation (SSF) with broken dried chestnut by probiotic lactic acid bacteria (LAB), namely Lactobacillus casei strain CU (CU) and Lactobacillus fermentum strain KF5 (KF5) was evaluated. Preliminary sensory evaluation results showed that fermented chestnut had unique flavor characteristics between perception of sour and of chestnut. The number of LABs in fermented chestnut samples was not less than 8 log10 cfu/g under the condition of 40 days storage at 4°C. Chestnut fermented with KF5 had a slightly better antioxidant activity to reduce the 1,1-Diphenyl-2-picrylhydrazyl (DPPH) free radical of 87% than the unfermented control (70.12%). Significant increases of 10.53% and 21.16% in protein digestibility of samples were observed following SSF with CU and KF5, respectively. The extracts of the fermented chestnut showed a less intense band just below 25 kDa in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The gas chromatography-mass spectrometer (GC-MS) extracellular metabolite analysis showed that the complex macromolecules in chestnut was degraded into simple sugars, organic acids, amino acids, and fatty acids. The findings of the study provide the possibility of using fermented chestnuts as potential healthy functional food. Practical applications At present, the application scope of modern chestnut preservation technology is not very wide, which is limited by cost and other factors. Therefore, the development of in-depth processing technologies of chestnut is one of the important ways to have a positive influence on the chestnut market. Nowadays, people focus on functional foods that can give full play to the body's defensive function, regulate physiological rhythm, prevent diseases, and promote rehabilitation, rather than just satisfying appetite or nutrition. Consumer attention to consume probiotic foods contributing to the maintenance of a good state of health through their biologically active ingredients has been significantly increased. This topic combines the characteristic resources of chestnut with selected probiotic lactic acid bacteria (LAB) through food biotechnology and uses anaerobic solid-state fermentation (SSF) technology to develop healthy functional food with high nutritional value and in line with people's consumption concept: chestnut products with good nutritional flavor and probiotic functional, which further improves the nutritional value of products.

Enhancement of Biogas Production from Bundled Rice Straw Solid-State Fermentation by Adding Microbial Agents

Two contrasting garage-type solid-state fermentation experiments were designed at pilot scale to reveal the intensification process and effects of adding compound inoculants. Bundled rice straw and fresh pig manure were used as feedstock with a total solids concentration (w/w) of 20% under ambient temperatures of 26 to 35 oC. The characteristics of biogas production and variations in bacterial community composition were investigated. The results indicated that using microorganisms shortened the start time of anaerobic solid-state fermentation. The target methane content in the biogas production reached 30% 7 days before the control group. A target of 50% was reached 8 days before the control group. Throughout the fermentation cycle, the cumulative gas production of the experimental group was 1340 m3, which was 20.5% higher than the control group. Cumulative methane production increased by 45%. Clustering and principal coordinates analysis suggested that the addition of compound bacteria increased the diversity of the microbial community and stabilized its structure, thus improving gas production efficiency and methane purity. These findings can assist future bioaugmentation research pertaining to the application of composite microbial agents.

Bio-hythane production from residual biomass of Chlorella sp. biomass through a two-stage anaerobic digestion

Residual Chlorella sp. biomass obtained after anaerobic solid-state fermentation was used to produce bio-hythane. The residual biomass was pretreated using acid, thermal, and acid-thermal methods before their respective hydrolysates were used in dark fermentation followed by the methanogenesis of anaerobic digestion to produce hydrogen and methane, respectively. Pretreatment of the residual biomass using acid and thermal methods did not significantly increase reducing sugar production. However, a maximum reducing sugar content of 28.9 mg-reducing-sugar·g-biomass−1 was attained using an acid-thermal method, resulting in the highest hydrogen and methane yields of 12.5 and 81 mL·g-volatile-solid−1, respectively. This was equivalent to the total energy yield of 3.03 kJ·g-VS−1 or 4.6% energy recovery, based on the heating value of the residual biomass.

A sequential process of anaerobic solid-state fermentation followed by dark fermentation for bio-hydrogen production from Chlorella sp.

Microalgal biomass has recently been one of the most widely studied feedstocks for bio-hydrogen production, owing to its richness in fermentable components, e.g. polysaccharides and proteins, and high biomass productivity. In this study, biomass of microalga Chlorella sp. TISTR 8411 was converted to hydrogen through a sequential process consisting of an anaerobic solid-state fermentation (ASSF) followed by a dark fermentation. The microalga was grown photoautothrophically in 80-L rectangular glass tanks and then scaled-up to a 240-L open pond for the production of biomass. The highest biomass concentration attained was 4.45 g L−1. The biomass was harvested with over 90% flocculation efficiency at pH 11.5 and a biomass concentration of 2.6 g/L. The sequential process gave a total hydrogen yield (HY) of 16.2 mL/g-volatile-solid (VS), of which 11.6 mL/g-VS was from ASSF. The high HY obtained from the ASSF indicated that it was effective and could be integrated with a conventional hydrogen production process to improve energy recovery from biomass.

Carboxylic acid production from ensiled crops in anaerobic solid-state fermentation - trace elements as pH controlling agents support microbial chain elongation with lactic acid.

For the production of carboxylic acid platform chemicals like medium-chain fatty acids (MCFA) by anaerobic fermentation, pH control is required. However, adding buffer solutions is ineffective in leach-bed reactors. In order to increase the MCFA production by maize silage fermentation and to engineer the process we investigated the effect of solid alkaline iron and manganese additives on the process performance and microbial community dynamics. Without additives, the pH dropped to 3.9 and lactic acid bacteria were favored. Total product yields of 207 ± 5.4 g organic acids (C2-C6) and alcohols per kg volatile solids were reached. The addition of trace elements increased the pH value and the product spectrum and yields changed. With a commercial iron additive, the product yields were higher (293 ± 15.2 g/kgvolatile solids) and supposedly clostridia used lactic acid for microbial chain elongation of acetic acid producing n-butyric acid. With the addition of pure Fe(OH)3 or Mn(OH)2, the total product yields were lower than in the other reactors. However, increased production of MCFA and the occurrence of distinct bacterial taxa (Lachnospiraceae, Ruminococcaceae and Megasphaera) related to this metabolic function were observed. The application of alkaline trace metal additives as pH stabilizing agents can mitigate spatial metabolic heterogeneities when trace metal deficient substrates like specific crops or residues thereof are applied.

Anaerobic solid-state fermentation of bio-hydrogen from microalgal Chlorella sp. biomass

A considerable amount of volatile solids (VS) contained in the biomass of microalgae makes it promising for use as feedstock in fermentation processes. In this study, a biomass of microalga Chlorella sp. was used as a sole substrate for hydrogen production in an anaerobic solid-state fermentation (ASSF). Optimization of the process was investigated on the selected critical variables, i.e., total solid (TS) content, initial pH, and feed to inoculum (F/I) ratio (on a VS basis) using response surface methodology (RSM) with central composite design (CCD). TS content and F/I ratio were found to have statistically significant effects on hydrogen production. Maximal hydrogen production of 165 ± 12 mL H2, equivalent to 18.58 mL H2/g VS and 0.28 L H2/L reactor·d, was achieved under the optimal conditions of 38.83% TS, pH 6.03, and an F/I ratio of 4.33. Acetic and butyric acids were found to be main soluble microbial products (SMPs) in the fermented biomass. Based on the compositions of the biomass, an equation for theoretical bioconversion of Chlorella sp. biomass to hydrogen was proposed.

A fermented tea with high levels of gallic acid processed by anaerobic solid-state fermentation

Microbial tea products are widely welcomed for their unique quality characteristics. However, the quality characteristics of pickled tea, a microbial tea product traditionally consumed in most Asian countries remain unclear. Therefore, the quality characteristics of pickled tea processed using Camellia sinensis leaves through anaerobic solid-state fermentation were analyzed. During 60-d fermentation, the free amino acids, caffeine, and tea polyphenols in pickled tea kept much stable, the soluble sugar content showed significant and continuous decrease, but the water extract showed a continuously increasing trend. The optimal fermentation time for pickled tea was 30 d, at which its normal quality characteristics were formed: the sensory quality was the best, most free amino acids evidently increased, a high level of gallic acid was produced up to 25.7 g/kg, and volatile compounds were mainly alkanes such as heptadecane and hexadecane. It is the first report that high levels of gallic acid in a microbe-fermented tea processed by anaerobic fermentation reached to that levels in Galla chinensis, which will benefit development of a functional tea with high levels of active components and understanding the microbial transformation of tea components through anaerobic fermentation.

Biohydrogen Production from Mushroom Cultivation Waste by Anaerobic Solid‐state Fermentation

AbstractMushroom cultivation waste (MCW) is a polypropylene bag stuffed with wood flour and nutrients for growing mushroom, which is a feasible feedstock for anaerobic biohydrogen production owing to its abundant availability, high organic and nutrient content. This study optimized the seed inoculum from various waste sludges (sewage sludge, cow dung and pig slurry), nutrient addition and operation conditions (moisture content and MCW powder particle size) for maximal biohydrogen production by solid‐state fermentation (SSF). SSF batch test was operated at a MCW 3 g total volatile solid (TVS)/L, temperature 55 °C and rotation speed of 15 rpm with a vertical rotative shaker. The peak hydrogen production performance of hydrogen production rate (HPR) 9.50 mol H2/kg‐d and hydrogen yield (HY) 0.29 mmol H2/g TVS) are obtained using sewage sludge 2 seed inoculum, nutrients addition, moisture content 70 % and particle size of 1.190∼0.590 mm. The results show that the MCW has the potential for hydrogen production by anaerobic mixed microflora using solid‐state fermentation. The bioenergy of 1842 kWh while using SSF to conver MCW to produce biohydrogen and it could reduce CO2 emission of 114–178 kg per year comparing using fossil fuel such as coal, fuel oil and natural gas.

Anaerobic Solid State Fermentation of Porcine Blood

An anaerobic solid state fermentation (ASSF) of porcine blood by two ferment agents was investigated. The free amino acids (FAA) content was applied as reference indicator, response surface design of Box-Behnken (BBD) was used to select the optimum conditions of ASSF of porcine blood. The optimum conditions were determined as porcine blood moisture of 76.0%, fermentation time of 7d, fermentation temperature of 39.0±0.5 oC, addition of the components of the mixture as follows: wheat bran 10.8 g , corn flour 1.2 g, Active 99 ferment agent I 0.768 g, Active 99 ferment agent II 0.19 g, porcine blood 86.0 g, resulting in FAA content of 23.8 mg/g. Evaluation experiments revealed that FAA content of 22.9 mg/g, which was 96.2% of the predicted value using Eq.2, and achieved a 14-fold increase comparing with the 1.5 mg/g which is the FAA content of unfermented mixture. It was confirmed that the protein of porcine blood was degraded into small peptides by Sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE).

Modeling of rotating drum bioreactor for anaerobic solid-state fermentation

Solid-state fermentation (SSF) has received more attention and has been applied to production of different products in recent years, especially biofuel production. The major problems to overcome in large-scale SSF are heat accumulation and heterogeneous distribution in a complex gas–liquid–solid multiphase bioreactor (or fermenter) system. In this work, a mathematical model of a rotating drum bioreactor for anaerobic SSF is developed considering the radial temperature distribution in the substrate bed. Validation experiments were conducted in a 5 m 3 pilot plant fermenter for production of fuel ethanol from milled sweet sorghum stalks. The model that was developed fit well with the experimental data. From these results, it was concluded that this mathematical model is a powerful tool to investigate the design and scale-up of an anaerobic SSF fermenter in the application of bioethanol production using cellulosic materials such as sweet sorghum stalks.

Two-particle model of anaerobic solid state fermentation

A structured mathematical model of anaerobic solid state fermentation (ASSF) has been developed. Since a stable ASSF requires addition of significant quantities of methanogenic seed sludge and mass-transfer limitation becomes important, the model postulates the existence of two different types of particles inside the fermenting solid mass--so-called "seed" particles with low biodegradability and high methanogenic activity and so-called "waste" particles with high biodegradability and low methanogenic activity. Any particle is assumed to be a completely mixed reactor and mass transfer of solutes between the particles is brought about by diffusion. The model includes multiple-reaction stoichiometry, microbial growth kinetics, material balances, liquid-gas interactions and liquid phase equilibrium chemistry. The theoretical model agrees on the qualitative level with existing experimental studies of ASSF. Hypothetical computer simulations are presented to illustrate the influence of biodegradability and mass transfer intensity on the stability of ASSF. On this basis, possible measures are proposed to prevent accumulation of volatile fatty acids inside the "seed" particles beyond their assimilative methanogenic capacity.

Solid-state fermentation of sugars in sweet sorghum

The sugars in unsterilized sweet sorghum solids fermented readily during anaerobic solid-state fermentation (SSF). Products, based on 100 g hexose, were: 36.7 g volatiles (mass loss), 32.8 g ethanol, 2.8 g glycerol, 12.7 g lactic acid, 2.0 g acetic acid, 4.8 g dextrans, and 4.2 g mannitol, presumably from fermentation with naturally occurring heterolactic bacteria, such as Leuconostoc dextranicum, as well as wild yeasts. Inoculation of unsterilized sorghum solids with 0.007% to 0.20% Saccharomyces cerevisiae increased fermentation rate, gas evolution, and yields of ethanol, glycerol, and acetic acid, while other yields decreased. With 0.2% yeast, yields were 40.9 g ethanol, 4.8 g glycerol, and 45.5 g gases. The volatiles from all fermentations had a strong odor of acetaldehyde. Compared with yields expected from the Pasteur equation, the ratio of mass loss to ethanol yield was 17% greater and glycerol yield was 50% greater, which suggests that significant amounts of acetaldehyde evaporated with CO 2 during SSF and Neuberg's second form of fermentation occurred to a much larger extent during SSF than in liquid phase fermentations.

Anaerobic solid state fermentation of cellulosic substrates with possible application to cellulase production

A solid state fermentation process was developed for the conversion of straw and cellulose under anaerobic conditions by a mixed culture of cellulolytic and methanogenic organisms. The bioconversion rate and efficiency were compared under mesophilic (35° C) and thermophilic (55° C) conditions. Cellulolytic activity was assayed in terms of sugar and overall soluble organic matter (chemical oxygen demand, COD) production. Maximum conversion rates were obtained under thermophilic conditions, i.e. 8.4 g and 14.2 g COD/kg·d, respectively, when wheat straw and cellulose were used as substrates. The cellulolytic activity of the reactor contents (23% dry matter), measured under substrate excess conditions, amounted to 50 g COD/kg·d. As a comparison, the activity of rumen contents (15% dry matter) measured by the same assay amounted to 150 g COD/kg·d. The anaerobic cellulases appeared to be substrate bound. This and the relative low activity levels attained, limit the perspectives of producing cellulase enzymes by this type of process.