Pilot-Scale Gas Double-Dynamic Solid-State Fermentation for the Production of Industrial Enzymes

Valorising pasta industry wastes by the scale up and integration of solid-state and liquid-submerged fermentations

Pasta waste has previously been studied in a process to obtain lactic acid through a sequential hydrolysis and fermentation. The process was improved by using enzymes produced via solid-state fermentation of wheat bran in shake flasks. However, the scale-up of the solid-state fermentation is a complex task. In this study, amylase was produced in a home-designed tray bioreactor which allowed to carry out the hydrolysis and fermentation steps at the pilot scale. Due to the efficiency of the solid-state fermentation and the activity of the enzyme, only a small amount (100 g) of wheat bran was required to achieve high yields in a hydrolysis in a 72 L bioreactor (50 L working volume). Overall, the lactic acid yield was 0.68 gLA/gdS, and after the purification, the lactic acid recovered was 55 %, with a total ion concentration of 500 mg/L and an enantiomeric purity of 98.1 % L-LA.

Comparison of Liquid and Solid-State Fermentation Processes for the Production of Enzymes and Beta-Glucan from Hulled Barley

Solid-state fermentation using hulled barley was carried out to produce enzymes and β-glucan. The one-factor-at-a-time experiments were carried out to determine the optimal composition of the basal medium. The modified synthetic medium composition in liquid-state fermentation was determined to be 70 g/l hulled barley, 0 g/l rice bran, 5 g/l soytone, and 6 g/l ascorbic acid. Optimal pretreatment conditions of hulled barley by solid-state fermentation were evaluated in terms of maximum production of fungal biomass, amylase, protease, and β-glucan, which were 1.26 mg/g, 31310.34 U/g, 2614.95 U/g, and 14.6% (w/w), respectively, at 60 min of pretreatment condition. Thus, the solid-state fermentation process was found to enhance the overall fermentation yields of hulled barley to produce high amounts of enzymes and β-glucan.

It Works! Organic-Waste-Assisted Trichoderma spp. Solid-State Fermentation on Agricultural Digestate

This study aimed at valorizing digestate through Trichoderma spp. solid-state fermentation (SSF) to produce a potentially ameliorated fertilizer combined with fungal biomass as a value-added bioproduct. Plant-growth-promoting Trichoderma atroviride Ta13, T. reesei RUT-C30, T. asperellum R, and T. harzianum T-22 were tested on different SSF substrates: whole digestate (WD), digestate dried up with wood sawdust (SSF1), and digestate enriched with food waste and dried up with wood sawdust (SSF2). The fungal biomass was quantified by using a qPCR assay. The growth of the four Trichoderma spp. was only observed on the SSF2 substrate. The highest quantity of mycelium was produced by T. reesei RUT-30 (689.80 ± 80.53 mg/g substrate), followed by T. atroviride Ta13, and T. asperellum R (584.24 ± 13.36 and 444.79 ± 91.02 mg/g substrate). The germination of Lepidium sativum seeds was evaluated in order to assess the phytoxicity of the Trichoderma-enriched substrate. The treatments with 7.5% SSF2-R, 3.75% SSF2-T-22, and 1.8% SSF2-Ta13 equally enhanced the root elongation in comparison to the non-fermented SSF-2. This study demonstrated that digestate, mixed with agro-food waste, was able to support the cultivation of Trichoderma spp., paving the way to the valorization of fermented digestate as a proper biofertilizer.

Large-scale production of enzymes for biotechnology uses

Enzymes are biocatalysts that speed up the chemical reaction to obtain the final valuable product/s. Biotechnology has revolutionized the use of traditional enzymes to be applicable in industries such as food, beverage, personal and household care, agriculture, bioenergy, pharmaceutical, and various other segments. With respect to the exponential growth of enzymes in biotech industries, it becomes important to highlight the advancements and impact of enzyme technology over recent years. In this review article, we discuss the existing and emerging production approaches, applications, developments, and global need for enzymes. Special emphasis is given to the predominantly utilized hydrolytic microbial enzymes in industrial bioprocesses.

Improving enzyme production by solid-state cultivation in packed-bed bioreactors by changing bed porosity and airflow distribution

Enzymes production by solid-state cultivation in packed-bed bioreactor needs to be improved by mathematical modeling and also by experimentation. In this work, a mixture of sugarcane bagasse and wheat bran was used for the growth of the fungus Myceliophthora thermophila I-1D3b, able to secrete endoglucanase and xylanase, enzymes of interest in the second-generation ethanol production. Bench and pilot-scale bioreactors were used for the experiments, while critical parameters as bed porosity and airflow distribution were evaluated. Results showed enzymes with higher activities for the most porous medium, even though the less substrate amount to be cultivated. For the pilot-scale bioreactor, only the most porous medium was evaluated using different airflow distribution techniques. Using an inner tube for air supply resulted in more homogeneous enzyme production, with higher activities. The results here presented will be helpful for the scale-up of this class of bioreactor into industrial apparatuses.

Production of high-value bioproducts enriched with γ-linolenic acid and β-carotene by filamentous fungi Umbelopsis isabellina using solid-state fermentations

Solid-state fermentation is a useful tool for utilizing different plant-based materials as cultivation substrates in order to produce potentially high-value fermented bioproducts. The aim of the present study was to successfully prepare various types of such bioproducts, using a zygomycetous strain Umbelopsis isabellina CCF2412. Various legume and cereal substrates were utilized effectively, while a few of them were obtained from agricultural waste, which is particularly advantageous from ecological and economic point of view. A common feature of the produced fermented materials was the increased content of different polyunsaturated fatty acids and carotenoid pigments in these bioproducts. Subsequent to the optimization of the solid-state fermentation process using cornmeal as the cultivation substrate, bioproducts enriched with γ-linolenic acid (11.45 mg γ-linolenic acid per gram of bioproduct), β-carotene (50.90 μg β-carotene per gram of bioproduct), and various microbial sterols were obtained. Appropriate n–6/n–3 acid ratio and enrichment of other microbial substances, such as the pigments and sterols mentioned above, in the fermented bioproducts widens the applicability of these bioproducts in different industries. The fermented cereal bioproducts produced in the present study from fermented wheat bran substrate were used for evaluating their application as feed for broiler chicken, and satisfactory results were obtained. Therefore, the present study creates novel opportunities for improving the quality of fermented bioproducts obtained during solid-state fermentation processes, especially for application in the feed industry.

Humidity Control Strategies for Solid-State Fermentation: Capillary Water Supply by Water-Retention Materials and Negative-Pressure Auto-controlled Irrigation

Solid-state fermentation (SSF) has regained interest owing to its advantages in solid waste treatment and fermentation industries. However, heterogeneous heat and mass transfer are often caused by the absence of free water and noticeable water loss from microbial utilization and moisture evaporation in SSF. It is necessary to explore more effective ways to solve issues of water loss and water supplement in SSF based on online capillary water monitoring, because capillary water is the dominant form of water that is present and lost in substrate. Two novel capillary-water supply strategies were proposed, established and evaluated using three selected reference strains, including water-retention materials and negative-pressure auto-controlled irrigation (NPACI). This study employed superabsorbent polymer, a kind of water-retention material to enhance enzyme productivity with the most significant increase of 2.47 times. Moreover, the combination of NPACI and 0.1% superabsorbent polymers increased productivity by 2.80-fold, together with lowered gradients of temperature, moisture and products. Furthermore, a modified liquid-supply SSF was constructed through successful capillary water control by proposed humidity control strategies. This modified SSF system could address the shortcomings of inhomogeneous culture of traditional SSF.

Two-steps gas double-dynamic solid-state fermentation enhances growth and spore production of Conithyrium minitans

Gas double-dynamic solid-state fermentation (SSF) is a promising strategy with the potential in transforming open-pattern fermentation into closed-pattern fermentation. This paper investigated gas double-dynamic SSF performance in cultivating Coniothyrium minitans (C. minitans), as well as its effect on physiology of C. minitans. Results showed that gas double-dynamic increased biomass content by 48.6%. High temperature impeded pycnidia formation and increased glycine production. More pycnidia formed in solid matrix at 20 °C, which was responsible for higher conidia production (1.5 (±0.03) × 10¹⁰ spores/g dry mass), indicating decisive role of high temperature in pycnidia formation of C. minitans in solid-state fermentation. Higher glycine content may be the response of high temperature stress which has close relationship with pycnidia and conidia production. Based on the findings, a two-step strategy for gas double-dynamic SSF was proposed and an satisfactory conidia production was obtained while fermentation period shortened.

Enzymatic saccharification of lignocellulosic biorefinery: Research focuses

To realize lignocellulosic biorefinery is of global interest, with enzymatic saccharification presenting an essential stage to convert polymeric sugars to mono-sugars for fermentation use. This mini-review summarizes qualitatively the research focuses discussed the review articles presented in the past 22 months and other relevant papers. The research focuses on pretreatment with improved efficiency, enhanced enzyme production with high yields and high extreme tolerance, feasible combined saccharification and fermentation processes, detailed mechanisms corresponding to the enzymatic saccharification in lignocellulosic biorefinery, and the costs are discussed.

Bioreactors in solid state fermentation technology: Design, applications and engineering aspects

In recent years, substantial credibility in employing Solid-State Fermentation (SSF) technique has been witnessed owing to its numerous advantages over submerged fermentation (SmF). In spite of enormous advantages, true potential of SSF technology has not been fully realized at industrial scale. The lack of rational and scalable bioreactor designs backed by mathematical models and automated control system that could successfully address heterogeneity with respect to heat and mass, and also operate aseptically, remains the prime reason for it. As a result, there still exists vast scope in SSF bioreactor research and development to facilitate broad spectrum of biotechnological applications. The present article reviews state-of-the-art in SSF technology with focus on bioreactors that have been employed for bioprocess applications, in particular, enzyme production. Based on the mode of operation, bioreactors are divided into four categories with emphasis on design features, effect of operating conditions on productivity, applications and limitations. Selected modeling studies developed over the years, have been revised and presented in problem specific manner in order to address the limitations. Some interesting designs including few recent ones that have been proposed and/or employed at pilot and industrial levels are discussed in more detail.

Solid state fermentation (SSF): diversity of applications to valorize waste and biomass

Solid state fermentation is currently used in a range of applications including classical applications, such as enzyme or antibiotic production, recently developed products, such as bioactive compounds and organic acids, new trends regarding bioethanol and biodiesel as sources of alternative energy, and biosurfactant molecules with environmental purposes of valorising unexploited biomass. This work summarizes the diversity of applications of solid state fermentation to valorize biomass regarding alternative energy and environmental purposes. The success of applying solid state fermentation to a specific process is affected by the nature of specific microorganisms and substrates. An exhaustive number of microorganisms able to grow in a solid matrix are presented, including fungus such as Aspergillus or Penicillum for antibiotics, Rhizopus for bioactive compounds, Mortierella for biodiesel to bacteria, Bacillus for biosurfactant production, or yeast for bioethanol.

A novel solid state fermentation coupled with gas stripping enhancing the sweet sorghum stalk conversion performance for bioethanol

BACKGROUND

Bioethanol production from biomass is becoming a hot topic internationally. Traditional static solid state fermentation (TS-SSF) for bioethanol production is similar to the traditional method of intermittent operation. The main problems of its large-scale intensive production are the low efficiency of mass and heat transfer and the high ethanol inhibition effect. In order to achieve continuous production and high conversion efficiency, gas stripping solid state fermentation (GS-SSF) for bioethanol production from sweet sorghum stalk (SSS) was systematically investigated in the present study.

RESULTS

TS-SSF and GS-SSF were conducted and evaluated based on different SSS particle thicknesses under identical conditions. The ethanol yield reached 22.7 g/100 g dry SSS during GS-SSF, which was obviously higher than that during TS-SSF. The optimal initial gas stripping time, gas stripping temperature, fermentation time, and particle thickness of GS-SSF were 10 h, 35°C, 28 h, and 0.15 cm, respectively, and the corresponding ethanol stripping efficiency was 77.5%. The ethanol yield apparently increased by 30% with the particle thickness decreasing from 0.4 cm to 0.05 cm during GS-SSF. Meanwhile, the ethanol yield increased by 6% to 10% during GS-SSF compared with that during TS-SSF under the same particle thickness. The results revealed that gas stripping removed the ethanol inhibition effect and improved the mass and heat transfer efficiency, and hence strongly enhanced the solid state fermentation (SSF) performance of SSS. GS-SSF also eliminated the need for separate reactors and further simplified the bioethanol production process from SSS. As a result, a continuous conversion process of SSS and online separation of bioethanol were achieved by GS-SSF.

CONCLUSIONS

SSF coupled with gas stripping meet the requirements of high yield and efficient industrial bioethanol production. It should be a novel bioconversion process for bioethanol production from SSS biomass.