Fungal solid state fermentation — an overview

Effects of the Incubation Period of Pleurotus ostreatus on the Chemical Composition and Nutrient Availability of Solid-State-Fermented Corn Stover

The current study aimed to optimize and improve the feeding value of Pleurotus ostreatus-fermented corn stover by evaluating the effects of five solid-state fermentation times and three in vitro fermentation periods on the chemical composition, dry matter disappearance (DMD), microbial mass and volatile fatty acid (VFA) production of treated and untreated corn stover. The study utilized a 3 × 5 factorial design, with eight replicates per treatment. Dry matter, crude protein (CP), ash and non-fiber carbohydrate (NFC) contents increased quadratically (p < 0.05) with increases in the solid-state fermentation time. Increases of 44.4-59.1%, 20.6-78.6% and 40.5-121% were noted for the CP, ash and NFC contents, respectively. Organic matter, ether extract, neutral detergent fiber and hemicellulose contents decreased quadratically (p < 0.05) across the treatments. Similar trends were noted for DM and fiber disappearance in the treatments. The total gas production and in vitro true dry matter digestibility (IVTDMD) increased quadratically, while microbial mass and in vitro apparent DMD increased in a linear manner. The total VFA, propionate and butyrate contents increased linearly. Both the acetate content and the A:P ratio decreased in a linear manner. The results show that the rumen fermentation pathway favors the production of propionate, with increases in propionate production of 7.46 and 8.30% after 2 and 4 wk, respectively. The study showed that a 2 wk period of solid-state fermentation is sufficient to provide a bio-transformed cow-calf feed resource from P. ostreatus-treated corn stover.

Solid-state fermentation in an earthen vessel: Trichoderma viride spore-based biopesticide production using corn cobs

The present study reports the production of Trichoderma viride spores in an earthen vessel using corn cobs. Using 4 kg of corn cobs, spore-based biopesticide was produced after 21 d with a maximum spore count of 2.50 × 109 spores/g of substrate and a moisture reduction from 70.80% w/v to 8.10% w/v. The gas chromatography-mass spectrometry analysis of its ethyl acetate extract revealed that it had 20 secondary metabolites, of which 13 were known to be antimicrobial, one was plant growth-promoting, and one performed both functions. Dried extract dissolved in methanol showed the minimum fungicidal concentration of 5-10 mg/ml against Rhizoctonia solani on potato dextrose agar plate. Plate assays and pot experiments on Rhizoctonia solani-infected potato plants exhibited good antifungal and plant growth-promoting activities. The biopesticide showed 71.28% viability over 10 m of storage in the same earthen vessel at 30 ± 2 °C. Thus, a simple, robust technology was developed with good potential for farm deployment.

Pullulanase: unleashing the power of enzyme with a promising future in the food industry

Pullulanases are the most important industrial group of enzymes in family 13 glycosyl hydrolases. They hydrolyze either α-1,6 and α-1,4 or both glycosidic bonds in pullulan as well as other carbohydrates to produce glucose, maltose, and maltotriose syrups, which have important uses in food and other related sectors. However, very less reports are available on pullulanase production from native strains because of low yield issues. In line with the increasing demands for pullulanase, it has become important to search for novel pullulanase-producing microorganisms with high yields. Moreover, high production costs and low yield are major limitations in the industrial production of pullulanase enzymes. The production cost of pullulanase by using the solid-state fermentation (SSF) process can be minimized by selecting agro-industrial waste. This review summarizes the types, sources, production strategies, and potential applications of pullulanase in different food and other related industries. Researchers should focus on fungal strains producing pullulanase for better yield and low production costs by using agro-waste. It will prove a better enzyme in different food processing industries and will surely reduce the cost of products.

Production of Glucoamylase from Novel Strain of Alternaria Alternata under Solid State Fermentation

Glucoamylase has an essential role as biocatalyst in various important industries of Pakistan. It is synthesized by using various fungal and bacterial strains, and different ecocultural conditions are applied under solid substrate fermentation method (SSF) to get the highest yield of glucoamylase. Alternaria alternata is an important fungus that can grow on industrial raw material like wheat bran, dried potato powder, tea leaves, rice husk, and sugar cane peel which are used as substrate. Among all, dried potato powder (10g) proved the best fermentation media for growth of fungal strain as well as maximum glucoamylase producer. Moreover, several chemical and physical states were also explored through solid substrate fermentation technique on glucoamylase yield. The highest glucoamylase production was recorded after 72 hours incubation in incubation chamber with 10g raw substrate, 1ml inoculum spore solution, 30°C temperature, and 5 pH. Further, phosphate buffer (5 pH) as moistening agent, 5% starch concentration and media additive as nitrogen (yeast extract), and carbon source (maltose) were screened for maximum glucoamylase titer (17.3 ± 0.05a°U/ml/min) and the highest specific activity (39.2U/mg). These cultural conditions were most appropriate for growth of A. alternata on solid media and production of highest glucoamylase under solid state fermentation procedure that could be utilized for commercial synthesis of glucoamylase.

Bioprocessing of pineapple waste biomass for sustainable production of bioactive compounds with high antioxidant activity

The effect of temperature, moisture content and pH during solid-state fermentation (SSF) of MD2 pineapple peel with Rhizopus oryzae (MUCL 28168) was evaluated on the release of bioactive compounds with antioxidant capacity. Applying a central composite design, it was found that temperature had a significant effect (p < 0.05) on the total phenolic content and DPPH antioxidant activity while for the ABTS radical elimination activity, the factor that presented a significant effect was the pH (p < 0.05); as this factor increases, the antioxidant activity enhances. The optimal conditions for fermentation process were 80% of moisture content, pH 5.5, temperature 37.3 °C and 24 h of process to maximize phenolic content and antioxidant activity. Gallic acid, chlorogenic acid, caffeic acid and cinnamic acid were identified in the extracts by HPLC analysis. These results permit to conclude that SSF of pineapple peel is an effective bioprocess for the release of phenolic compounds with antioxidant activity.

Graphical abstract

Valorization of Brewer’s Spent Grain Using Biological Treatments and its Application in Feeds for European Seabass (Dicentrarchus labrax)

Brewer’s spent grain (BSG) is the main brewery industry by-product, with potential applications in the feed and food industries due to its carbohydrate composition. In addition, the lignocellulosic nature of BSG makes it an adequate substrate for carbohydrases production. In this work, solid-state fermentation (SSF) of BSG was performed with Aspergillus ibericus, a non-mycotoxin producer fungus with a high capacity to hydrolyze the lignocellulosic matrix of the agro-industrial by-products. SSF was performed at different scales to produce a crude extract rich in cellulase and xylanase. The potential of the crude extract was tested in two different applications: -(1) - the enzymatic hydrolysis of the fermented BSG and (2) - as a supplement in aquafeeds. SSF of BSG increased the protein content from 25% to 29% (w/w), while the fiber content was reduced to 43%, and cellulose and hemicellulose contents were markedly reduced to around 15%. The scale-up of SSF from 10 g of dry BSG in flasks to 50 g or 400 g in tray-type bioreactors increased 55% and 25% production of cellulase and xylanase, up to 323 and 1073 U g⁻¹ BSG, respectively. The optimum temperature and pH of maximal activities were found to be 55°C and pH 4.4 for xylanase and 50°C and pH 3.9 for cellulase, cellulase being more thermostable than xylanase when exposed at temperatures from 45°C to 60°C. A Box–Behnken factorial design was applied to optimize the hydrolysis of the fermented BSG by crude extract. The crude extract load was a significant factor in sugars release, highlighting the role of hydrolytic enzymes, while the load of fermented BSG, and addition of a commercial β-glucosidase were responsible for the highest phenolic compounds and antioxidant activity release. The lyophilized crude extract (12,400 and 1050 U g⁻¹ lyophilized extract of xylanase and cellulase, respectively) was also tested as an enzyme supplement in aquafeed for European seabass (Dicentrarchus labrax) juveniles. The dietary supplementation with the crude extract significantly improved feed and protein utilization. The processing of BSG using biological treatments, such as SSF with A. ibericus, led to the production of a nutritionally enriched BSG and a crude extract with highly efficient carbohydrases capable of hydrolyzing lignocellulosic substrates, such as BSG, and with the potential to be used as feed enzymes with remarkable results in improving feed utilization of an important aquaculture fish species.

Challenges and opportunities in producing high-quality edible mushrooms from lignocellulosic biomass in a small scale

Mushrooms are high-value products that can be produced from lignocellulosic biomass. Mushrooms are the fruiting body of fungi and are domestically cultivated using lignocellulosic biomass obtained from agricultural byproducts and woody biomass. A handful of edible mushroom species are commercially cultivated at small, medium, and large scales for culinary and medicinal use. Details about different lignocellulosic biomass and their composition that are commonly used to produce mushrooms are outlined in this review. In addition, discussions on four major processing steps (i) producing solid and liquid spawn, (ii) conventional and mechanized processing lignocellulosic biomass substrates to produce mushroom beds, (iii) maintaining growth conditions in climate-controlled rooms, and (iv) energy requirements and managements to produce mushrooms are also provided. The new processing methods and technology outlined in this review may allow mushrooms to be economically and sustainably produced at a small scale to satisfy the growing food needs and create rural jobs. KEY POINTS: • Some of the challenges faced by small-scale mushroom growers are presented. This review is expected to stimulate more research to address the challenges.

Morphological growth pattern of Phanerochaete chrysosporium cultivated on different Miscanthus x giganteus biomass fractions

BACKGROUND

Solid-state fermentation is a fungal culture technique used to produce compounds and products of industrial interest. The growth behaviour of filamentous fungi on solid media is challenging to study due to the intermixity of the substrate and the growing organism. Several strategies are available to measure indirectly the fungal biomass during the fermentation such as following the biochemical production of mycelium-specific components or microscopic observation. The microscopic observation of the development of the mycelium, on lignocellulosic substrate, has not been reported. In this study, we set up an experimental protocol based on microscopy and image processing through which we investigated the growth pattern of Phanerochaete chrysosporium on different Miscanthus x giganteus biomass fractions.

RESULTS

Object coalescence, the occupied surface area, and radial expansion of the colony were measured in time. The substrate was sterilized by autoclaving, which could be considered a type of pre-treatment. The fastest growth rate was measured on the unfractionated biomass, followed by the soluble fraction of the biomass, then the residual solid fractions. The growth rate on the different fractions of the substrate was additive, suggesting that both the solid and soluble fractions were used by the fungus. Based on the FTIR analysis, there were differences in composition between the solid and soluble fractions of the substrate, but the main components for growth were always present. We propose using this novel method for measuring the very initial fungal growth by following the variation of the number of objects over time. Once growth is established, the growth can be followed by measurement of the occupied surface by the mycelium.

CONCLUSION

Our data showed that the growth was affected from the very beginning by the nature of the substrate. The most extensive colonization of the surface was observed with the unfractionated substrate containing both soluble and solid components. The methodology was practical and may be applied to investigate the growth of other fungi, including the influence of environmental parameters on the fungal growth.

Enrichment of laccase production by Phoma herbarum isolate KU4 under solid-state fermentation by optimizing RSM coefficients using genetic algorithm

The process parameters were optimized to obtain enhanced enzyme activity from the fungus Phoma herbarum isolate KU4 using rice straw and saw dust as substrate under solid-state fermentation using Response surface methodology (RSM). Genetic algorithm was used to validate the RSM for maximum laccase production. Six variables, viz., pH of the media, initial moisture content, copper sulphate concentration, concentration of tannic acid, inoculum concentration and incubation time were found to be effective and optimized for enhanced production. Maximum laccase production was achieved by RSM at pH 5·0 and 86% of initial moisture content of the culture medium, 150 µmol l^-1 of CuSO₄ , 1·5% tannic acid and 0·128 g inoculum g^-1 dry substrate inoculum size on the fourth day of fermentation. The highest laccase activity was observed as 79 008 U g^-1 , which is approximately sixfold enhanced production compared to the unoptimized condition (12 085·26 U g^-1 ).

The potential of fermentation on nutritional and technological improvement of cereal and legume flours: A review

Nowadays there is an increasing demand for vegetable protein sources as an alternative to that of animal origin, not only for its greater environmental sustainability but also for its relationship with lower risk of suffering cardiovascular diseases. Legumes, cereals and seeds are seen as a good proteinaceous source providing as well dietetic fiber and phytochemicals with antioxidant properties. However, their digestibility and bioavailability are limited by the presence of anti-nutritional factors (ANFs) but susceptible of being improved by soaking, cooking or fermentation. The objective of this work is to review the solid-state and submerged fermentation effect on nutritional and functional properties of legumes, cereals and seeds. The microorganisms involved (bacteria, fungus and yeasts) are able to produce enzymes that degrade ANFs giving rise to more digestible flours with a more interesting nutritional, sensorial and technological profile. Solid-state fermentation is more commonly used for its higher efficiency, accepting agro-industrial residues as substrates and its lower volume of effluents. Fermented legumes had their technological properties enhanced while an increment in antioxidant properties was characteristic of cereals. The present review highlights fermentation of cereals and legumes mainly as a key process that at industrial scale could generate new products with enhanced nutritional and technological properties.

A deep-sea hydrogen peroxide-stable alkaline serine protease from Aspergillus flavus

We report here the production of an alkaline serine protease by Aspergillus flavus isolated at 5600-m depth from deep-sea sediments of the Central Indian Basin. When grown on defatted groundnut oil meal at 30 °C for 48-72 h, this fungal isolate produced 2000-2500 ACU mL^-1 of alkaline protease. The purified protease had activity optima at pH 10.0 and 45 °C. It was a thiol-independent serine protease, identified as an alkaline serine protease ALP1 with a molecular mass of 42.57 kDa. The thermostability and activity of the enzyme increased at 60 °C, in the presence of additives such as sucrose, Tween 20, sorbitol, Ca²⁺ and glycerol and was not adversely affected by H₂O₂ indicating its potential as a detergent additive.

Solid-State Fermentation with Aspergillus niger GH1 to Enhance Polyphenolic Content and Antioxidative Activity of Castilla Rose (Purshia plicata)

This work was performed to study Castilla Rose (Purshia plicata) as a potential source of polyphenols obtained by solid-state fermentation (SSF)-assisted extraction using the microorganism Aspergillus niger GH1 and to evaluate the antioxidant activity of the extracted compounds. First, water absorption capacity (WAC) of the plant material, radial growth of the microorganism, determination of best fermentation conditions, and maximum accumulation time of polyphenols were tested. Then, a larger-scale fermentation, polyphenols isolation by column liquid chromatography (Amberlite XAD-16) and recovered compounds identification by HPLC-MS were made. Finally, the antioxidant activity of the recovered compounds was tested by ABTS, DPPH, and lipid oxidation inhibition assays. The best fermentation conditions were temperature 25 °C and inoculum 2 × 106 spores/g, while the maximum extraction time of polyphenols was 24 h (173.95 mg/g). The HPLC/MS analysis allowed the identification of 25 different polyphenolic compounds, and the antioxidant activity of the obtained polyphenols was demonstrated, showing ABTS assay the most effective with inhibition of 94.34%.

Tracing bacterial and fungal necromass dynamics of municipal sludge in landfill bioreactors using biomarker amino sugars

The dynamics of microbial necromass of municipal solid waste over long-term landfill remain unknown. This study presents the first investigation on the dynamics of bacterial and fungal necromass of municipal sludge in non-aeration versus alternating aeration landfill bioreactors by using amino sugar biomarkers. Results showed that under non-aeration treatment, the decomposition rate of muramic acid derived from bacteria is higher than that of fungal-derived glucosamine. The relative change in glucosamine and muramic acid in the early period of landfills under the alternating aeration treatment is consistent with that under non-aeration treatment. However, with the increase in alternating aeration cycles, bacterial necromass muramic acid exerts a lower decomposition rate than fungal necromass glucosamine. Throughout the entire landfill period, galactosamine is the amino sugar with the slowest decomposition rate under non-aeration mode but the amino sugar with the fastest decomposition rate under alternating aeration mode. The present work fills the knowledge gap of microbial necromass dynamics of municipal solid waste in landfills.

Laundry Detergent Compatibility and Dehairing Efficiency of Alkaline Thermostable Protease Produced from Aspergillus terreus under Solid-state Fermentation

Aspergillus terreus was chosen for production of alkaline protease using solid-state fermentation (SSF). The maximum enzyme yield reached about 34.87 U/mg protein after optimization of fermentation parameters. The produced alkaline protease was purified by precipitation with iso-propanol and then purified through gel filtration and ion exchange column chromatography with a yield of 53.58% and 5.09- fold purification. The enzyme has shown to have a molecular weight of 35 kDa. Optimal pH and temperature for the enzyme activity were 9.5 and 50°C respectively. The highest activity was reported towards casein, with an apparent Km value of 6.66 mg/mL and V_max was 30 U/mL. The enzyme activity was greatly repressed by phenylmethylsulfonyl fluoride (PMSF). Sodium dodecyl sulfate (SDS) caused activation in enzyme activity. The enzyme retained about 83.8, 70.6, 74.5, 76.4 and 66.4% of its original activity after incubation with Aerial, Leader, Oxi, Persil and Tide, respectively for 8 h at 60°C. Adding of the enzyme in detergents improved the cleansing performance to the blood stains and suggested to be used as a detergent additive. Our outcomes showed that protease could be used as environment green-approach in dehairing process.

Screening of potential IL-tolerant cellulases and their efficient saccharification of IL-pretreated lignocelluloses

Lignocellulosic biomass as one of the most abundant and renewable resources has great potential for biofuel production. The complete conversion of biomass to biofuel is achieved through the effective pretreatment process and the following enzyme saccharification. Ionic liquids (ILs) are considered as a green solvent for lignocellulose pretreatment. However, ILs exhibit an inhibitory effect on cellulase activity, leading to a subsequent decrease in the efficiency of saccharification. The screening of new potential IL-tolerant cellulases is important. In the current study, a fungal strain with a relatively high cellulase production was isolated and identified as Penicillium oxalicum HC6. The culture conditions were optimized using corn stover and peptone as the carbon source and nitrogen source at pH 4.0 and 30 °C with an inoculation size of 2% (v/v) for 8 days. It was found that P. oxalicum HC6 exhibited potential salt tolerance with the increase of the enzyme production at a salt concentration of 5.0% (w/v). In addition, high enzyme activities were obtained at pH 4.0–6.0 and 50–65 °C. The crude enzyme from P. oxalicum HC6 with good thermal stability was also stable in the presence of salt and ILs. Good yields of reducing sugar were obtained by the crude enzyme from P. oxalicum HC6 after the saccharification of corn stover that was pretreated by ILs. P. oxalicum HC6 with potentially salt-tolerant and IL-tolerant enzymes has great potential application in the enzymatic saccharification of lignocellulose.

Lignocellulosic biomass as one of the most abundant and renewable resources has great potential for biofuel production.

Challenges and opportunities of the bio-pesticides production by solid-state fermentation: filamentous fungi as a model

In recent years, production and use of bio-pesticides have increasing and replacing some synthetic chemical pesticides applied to food commodities. In this review, biological control is focused as an alternative, to some synthetic chemical treatments that cause environmental, human health, and food quality risks. In addition, several phytopathogenic microorganisms have developed resistance to some of these synthetic chemicals and become more difficult to control. Worldwide, the bio-pesticides market is growing annually at a rate of 44% in North America, 20% in Europe and Oceania, 10% in Latin and South American countries and 6% in Asia. Use of agro-industrial wastes and solid-state fermentation (SSF) technology offers an alternative to bio-pesticide production with advantages versus conventional submerged fermentations, as reduced cost and energy consumption, low production of residual water and high stability products. In this review, recent data about state of art regarding bio-pesticides production under SSF on agroindustrial wastes will be discussed. SSF can be defined as a microbial process that generally occurs on solid material in the absence of free water. This material has the ability to absorb water with or without soluble nutrients, since the substrate must have water to support the microorganism's growth and metabolism. Changes in water content are analyzed in order to select the conditions for a future process, where water stress can be combined with the best spore production conditions, obtaining in this way an inexpensive biotechnological option for modern agriculture in developing countries.

Inexpensive α-amylase production and application for fiber splitting in leather processing

Recently, the production of superior quality enzymes using waste sources has promoted greater research interest due to their enhanced enzyme activity, selectivity and stability.

Cellulase production by Aspergillus japonicus URM5620 using waste from castor bean (Ricinus communis L.) under solid-state fermentation

The activity of β-glucosidase (βG), total cellulase (FPase) and endoglucanase (CMCase), produced by Aspergillus japonicus URM5620, was studied on solid-state fermentation using castor bean meal as substrate. The effect of the substrate amount, initial moisture, pH, and temperature on cellulase production was studied using a full factorial design (2(4)). The maximum βG, FPase, and CMCase activity was 88.3, 953.4, and 191.6 U/g dry substrate, respectively. The best enzyme activities for all three enzymes were obtained at the same conditions with 5.0 g of substrate, initial moisture 15% at 25 °C and pH 6.0 with 120 h of fermentation. The optimum activity for FPase and CMCase was found at pH 3.0 at an optimum temperature of 50 °C for FPase and of 55 °C for CMCase. The cellulases were stable in the range of pH 3.0-10.0 at 50 °C temperature. The enzyme production optimization demonstrated clearly the impact of the process parameters on the yield of the cellulolytic enzymes.

Utilization of horticultural waste for laccase production by Trametes versicolor under solid-state fermentation

Horticultural waste collected from a landscape company in Singapore was utilized as the substrate for the production of laccase under solid-state fermentation by Trametes versicolor. The effects of substrate particle size, types of inducers, incubation temperature and time, initial medium pH value, and moisture content on laccase production were investigated. The optimum productivity of laccase (8.6 U/g substrate) was achieved by employing horticultural waste of particle size greater than 500 μm and using veratryl alcohol as the inducer. The culture was at 30 °C for 7 days at moisture content of solid substrate of 85% and initial pH 7.0. The decolorization was also investigated in order to assess the degrading capability of the ligninolytic laccase obtained in the above-mentioned cultures. The decolorization degree of a model dye, phenol red, was around 41.79% in 72 h of incubation. By far, this is the first report on the optimization of laccase production by T. versicolor under solid-state fermentation using horticultural waste as the substrate.

Production and partial characterization of arabinoxylan-degrading enzymes by Penicillium brasilianum under solid-state fermentation

The production of a battery of arabinoxylan-degrading enzymes by the fungus Penicillium brasilianum grown on brewer's spent grain (BSG) under solid-state fermentation was investigated. Initial moisture content, initial pH, temperature, and nitrogen source content were optimized to achieve maximum production of feruloyl esterase, xylanase, and alpha-L: -arabinofuranosidase. Under the optimum growth conditions (80% moisture, pH 6, 26.5 degrees C, and 5 g/l nitrogen source), the maximum level of feruloyl esterase (1,542 mU/g BSG) was found after 196 h, whereas xylanase (709 U/g BSG) and ArabF activity (3,567 mU/g BSG) were maximal after 108 h and 96 h, respectively. Based on substrate utilization data, the feruloyl esterases produced by P. brasilianum was anticipated to subclass B. A crude enzyme (CE) preparation from P. brasilianum culture grown on BSG was tested for the release of hydroxycinnamic acids and pentoses from BSG. The P. brasilianum CE produced in this work contains a balance of cell wall-modifying enzymes capable of degrading arabinoxylan of BSG by more than 40%.