Aerobic Solid-state Fermentation Research Articles

Multi-omics study of sulfur metabolism affecting functional microbial community succession during aerobic solid-state fermentation

Microbial-mediated sulfur metabolism is closely related to carbon and nitrogen metabolism in natural biological systems. In this study, the effects of sulfur metabolism on microbial communities and functional enzyme succession were investigated based on integrated multi-omics by adding sulfur-containing compounds to aerobic fermentation systems. Sulfur powder was oxidized to S2O32- and subsequently to SO42- by the microbial sulfur-oxidizing system, which lowered the pH to 7.5 on day 7. The decrease in pH resulted in Planifilum (secreted S8, M17 and M32 proteases) losing its competitive advantage, whereas Novibacillus (secreted M14 and M19 metalloproteases) became dominant. Structural proteomics indicated that the surface of Novibacillus proteases has more negatively charged amino acid residues that help maintain protein stability at low pH. These findings aid understanding of the effects of sulfur metabolism on fermentation and the mechanism of microbial adaptation after pH reduction, providing new perspectives on the optimization of fermentation processes.

A Critical Evaluation of Recent Studies on Packed-Bed Bioreactors for Solid-State Fermentation

Packed-bed bioreactors are often used for aerobic solid-state fermentation, since the forced aeration supplies O2 and removes metabolic heat from the bed. Motivated by the potential for applications in biorefineries, we review studies conducted on packed-bed bioreactors over the last decade, evaluating the insights these studies provide into how large-scale packed beds should be designed and operated. Many studies have used low superficial air velocities and suffer from preferential airflow, such that parts of the bed are not properly aerated. Moreover, some studies have proposed ineffective strategies, such as reversing the direction of the airflow or introducing air through perforated pipes within the bed. Additionally, many studies have used narrow water-jacketed packed-bed bioreactors, but these bioreactors do not reflect heat removal in wide large-scale packed beds, in which heat removal through the side walls makes a minor contribution. Finally, we conclude that, although some attention has been given to characterizing the porosities, water sorption isotherms and volumetric heat and mass transfer coefficients of substrate beds, this work needs to be extended to cover a wider range of solid substrates, and work needs to be done to characterize how these bed properties change due to microbial growth.

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.

Bioconversion of food waste to crayfish feed using solid-state fermentation with yeast.

In order to realize the value-added utilization of food waste (FW), the preparation of crayfish (Procambarus clarkii) feed by yeast fermentation was investigated. Firstly, the suitable fermentation condition was obtained through a single factor experiment as follows: the initial moisture of the FW was adjusted to 60% with bran and inoculated with a 2% yeast mixture (Saccharomyces cerevisiae, Candida utilis, and Yarrowia lipolytica, 3:2:1) followed by aerobic solid-state fermentation for 7days. The crude protein and acid-soluble protein contents in the fermented feed were 25.14% and 5.16%, which were increased by 8% and 140.67%, respectively. The crude fat content was 0.74%, decreased by 68.29%. The content of antioxidant glutathione (571.78μg/g) increased 63.33%, and the activities of protease and amylase increased nearly 9 and 3 times, respectively. The maximum degradation rates of aflatoxin B1, zearalenone, and deoxynivalenol were 63.83%, 77.52%, and 80.16%, respectively. The fermented feeds were evaluated by substituting (0%, 10%, 30%, 50%, and 100%) commercial diet for crayfish (30-day culture period). When the replacement proportion was 30%, the weight gain of crayfish reached 44.87% (initial body weight 13.98 ± 0.41g), which was significantly increased by 10.25% compared with the control (p = 0.0005). In addition, the lysozyme and SOD enzyme activities in crayfish hepatopancreas were also increased significantly. Our findings suggest that yeast-fermented feed from FW can replace 30% of crayfish's conventional diet, which may improve crayfish's antioxidant capacity and enhance non-specific immunity by providing molecules such as glutathione.

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.

Intellectualized Control System of Biofermenter

The most promising and demanded development lines of the present-day production are its intellectualization and robotic automation. The processing of organic agricultural waste traditionally features the least application of robots. One of the most advanced technologies for solid organic waste treatment is its aerobic solid-state fermentation. The intellectualized control system of a fermenter contributes to the final product quality enhancement: the self-heating rate of the fermented material is 44% higher and the temperature dispersion at the measurement points is 87% lower. The resulting reduction in energy consumption improves the profitability of this processing technology by 10% or more. Higher efficiency may be achieved by further refinement of the intellectualized control system of a fermenter.

Novel strategy of incorporating biochar in solid-state fermentation for enhancing erythritol production by forming “microzones”

Biochar is increasingly considered in addressing bioprocess issues due to its strong adsorbability and excellent compatibility to microbes. Here, biochar was first applied in aerobic solid-state fermentation (SSF) for erythritol production. Biochars derived from different agricultural wastes under various pyrolysis temperatures were evaluated, and wheat straw pyrolyzed at 300 °C (WSc) performed the best in enhancing fermentative erythritol production, with a dosage of 4% (w/w). In this procedure, cell–biochar–substrate “microzones” were formed, which was conductive to cell growth and attachment, and hence contributed enhanced enzyme activities, oil consumption, and erythritol production. The resultant erythritol productions of batch and fed-batch fermentations were 207.3 and 222.5 mg/gds, respectively. In repeated-batch fermentation, high cell viability and robust erythritol synthesis were maintained throughout seven cycles. This study demonstrates that SSF can be remarkably facilitated by biochar addition, suggesting a new perspective of biochar application in microbiological processes.

Cattle barn bedding from recycled manure: some veterinary, technological and economic aspects of application

Agriculture modernization is a topical issue for both the global and domestic economy. Intensification of livestock farming results in an increased production of manure. Recycling of manure into bedding is one of the modern utilization technologies. National regulations do not specify requirements for currently applied bedding types, including manure-based bedding. The foreign experience, however, demonstrates several economic, zootechnical and hygienic advantages of this material. The field veterinary study revealed the positive health effect of bedding. The cows housed without bedding featured threefold higher risk of surgical diseases of limbs. Technical and economic assessment of a dairy farm with 1000 dairy cows showed the following annual operating costs when the major part of manure was passively composted and a part of manure was recycled into the bedding by (1) aerobic solid-state fermentation in a chamber fermenter and finish drying in a dryer drum – 24.2 million roubles; (2) aerobic solid-state fermentation in a drum fermenter – 21.7 million roubles; and (3) thermal drying in a dryer drum – 27.5 million roubles. At the same time, if all manure produced was composted and the bedding was purchased from external sources, the costs would be 27.9 to 35.2 million roubles depending on the bedding material.

Improving cellulosic ethanol fermentation efficiency by converting endogenous water-soluble carbohydrates into citric acid before pretreatment.

Water-soluble carbohydrates in raw lignocellulosic biomass are converted into hydroxymethylfurfural (HMF) in the acid-based pretreatment, thus increasing the detoxification intensity and reducing the fermentation efficiency of cellulosic ethanol. Therefore, reducing water-soluble carbohydrates in raw corn stover is crucially important to reduce the inhibitors' generation and improve the ethanol fermentation efficiency. In this study, aerobic solid-state fermentation of corn stover by inoculating Aspergillus niger spores converted 83% of the endogenous water-soluble carbohydrates into citric acid, leading to the decrease of 41% of HMF generation and 8% of sulfuric acid usage during the dry acid pretreatment. The reduced inhibitor generation improved the ethanol fermentability by 11% more ethanol than that of the corn stover without water-soluble carbohydrates' removal. This suggests that the removal of the water-soluble carbohydrates before pretreatment significantly reduced the inhibitors' generation in pretreatment and improved the fermentation efficiency of cellulosic ethanol.

Detoxification of Aflatoxin B₁ by Zygosaccharomyces rouxii with Solid State Fermentation in Peanut Meal.

Aflatoxins are highly carcinogenic, teratogenetic, and morbigenous secondary metabolites of Aspergillus flavus and A. parasiticus that can contaminate multiple staple foods, such as peanut, maize, and tree nuts. In this study, Zygosaccharomyces rouxii was screened out and identified from fermented soy paste—one kind of traditional Chinese food—to detoxify aflatoxin B1 (AFB1) by aerobic solid state fermentation in peanut meal. The optimal degradation condition was chosen from single factor experiment, and the most effective detoxification rate was about 97%. As for liquid fermentation, we tested the binding ability of Z. rouxii, and the highest binding rate reached was 74.3% (nonviable cells of Z. rouxii) in phosphate-buffered saline (PBS). Moreover, the biotransformation of AFB1 through fermentation of Z. rouxii in peanut meal was further verified by liquid chromatography/mass spectrometry (LC/MS). According to TIC scan, after fermentation by Z. rouxii, the AFB1 in peanut meal was prominently degraded to the lowering peaks of AFB1. Additionally, m/s statistics demonstrated that AFB1 may be degraded to some new products whose structural properties may be different from AFB1, or the degradation products may be dissolved in the aqueous phase rather than the organic phase. As far as we know, this is the first report indicating that the safe strain of Z. rouxii has the ability to detoxify AFB1.

Extraction of bioactive plant materials by simultaneous enzyme treatment and lactic acid fermentation – a mini-review

ABSTRACTMany plants contain valuable compounds which could be used as pharmaceuticals, nutrients, or cosmetics, etc. The objective of the current review is to describe the ENLAC process (enzyme-assisted solid-state lactic acid fermentation) which enables the preservation of plant biomass and enhances the recovery of valuable natural compounds from plants. The advantages attributed to ENLAC include the possibility of preserving the plant biomass until extraction under mild temperature conditions. Using fibrolytic enzymes, it was possible to increase the yield of extracted protein, chlorophyll and β-carotene from alfalfa silages, and to enhance the extraction of polyphenols from ensiled sage and rosemary. A further development of the process included the use of enzymes produced in situ by fungi under aerobic solid-state fermentation, which lowered the estimated costs of ENLAC considerably. We hope that the review will encourage researchers to pursue ENLAC and develop useful applications for it.

Valorization of soy waste through SSF for the production of compost enriched with Bacillus thuringiensis with biopesticide properties

There is a growing generation of biodegradable wastes from different human activities from industrial to agricultural including home and recreational activities. On the other hand, agricultural and horticultural activities require significant amounts of organic amendments and pesticides. In this framework, the present study evaluates the viability of soy fiber residue valorization as organic soil amendment with biopesticide properties through aerobic solid-state fermentation (SSF) in the presence of Bacillus thuringiensis (Bt). The experiments were performed first under sterile and non-sterile conditions at lab scale using 115 g of sample and controlled temperature (30 °C). Bt growth was successful in sterile conditions, obtaining 6.2 × 1011 CFU g−1 DM and 8.6 × 1010 spores g−1 DM after 6 days. Bt survived on solid culture under non-sterile conditions (3.8 × 109 CFU g−1 DM and 1.3 × 108 spores g−1 DM). Further, the valorization process was scaled-up to 10 L reactors (2300 g) under non-sterile conditions obtaining a final stabilized material with viable Bt cells and spores (9.5 × 107 CFU g−1 DM and 1.1 × 108 spores g−1 DM in average) after 9 days of SSF. These results confirm the possibility of managing biodegradable wastes by their transformation to a waste derived soil amendment with enhanced biopesticide effect, in comparison to traditional compost using a valuable and low-cost technique (SSF).

Integrated delignification and simultaneous saccharification and fermentation of hard wood by a white-rot fungus, Phlebia sp. MG-60

We propose a new process of unified aerobic delignification and anaerobic saccharification and fermentation of wood by a single microorganism, the white-rot fungus Phlebia sp. MG-60. This fungus is able to selectively degrade lignin under aerobic solid state fermentation conditions, and to produce ethanol directly from delignified oak wood under semi-aerobic liquid culture conditions. After 56d aerobic incubation, 40.7% of initial lignin and negligible glucan were degraded. Then under semi-aerobic conditions without the addition of cellulase, 43.9% of theoretical maximum ethanol was produced after 20d. Changing from aerobic conditions (biological delignification pretreatment) to semi-aerobic conditions (saccharification and fermentation) enabled the fermentation of wood by solely biological processes. This is the first report of ethanol production from woody biomass using a single microorganism without addition of chemicals or enzymes.

Gaseous concentration gradients in tray type solid state fermentors ? Effect on yields and productivities

In aerobic solid state fermentation systems, interaction of mass transfer effects with bioreaction plays an important role on the yields and productivities of the bioreactors. Experimental observations on the oxygen and carbon dioxide concentration gradients in a tray type solid state fermentation system are reported in this paper. Steep gradients are experienced in deep beds making large portions of the bioreactor ineffective. The results are useful in the design of the bioreactor in terms of efficient mass transfer as well as critical thickness of the substrate bed to be used.