Showing papers on "Fermentation published in 2020"

Reviewing the potential of bio-hydrogen production by fermentation

Abstract: Hydrogen is a common reactant in the petro-chemical industry and moreover recognized as a potential fuel within the next 20 years The production of hydrogen from biomass and carbohydrate feedstock, though undoubtedly desirable and favored, is still at the level of laboratory or pilot scale The present work reviews the current researched pathways Different types of carbohydrates, and waste biomass are identified as feedstock for the fermentative bio-hydrogen production Although all techniques suffer from drawbacks of a low H2 yield and the production of a liquid waste stream rich in VFAs that needs further treatment, the technical advances foster the commercial utilization Bacterial strains capable of high hydrogen yield are assessed, together with advanced techniques of co-culture fermentation and metabolic engineering Residual VFAs can be converted The review provides an insight on how fermentation can be conducted for a wide spectrum of feedstock and how fermentation effluent can be valorized by integrating fermentation with other systems, leading to an improved industrial potential of the technique To boost the fermentation potential, additional research should firstly target its demonstration on pilot or industrial scale to prove the process efficiency, production costs and method reliability It should secondly focus on optimizing the micro-organism functionality, and should finally develop and demonstrate a viable valorization of the residual VFA-rich waste streams

Effects of lactic acid fermentation-based biotransformation on phenolic profiles, antioxidant capacity and flavor volatiles of apple juice

Abstract: Apple juice (AJ) was fermented by six select lactic acid bacteria (LAB), namely Lactobacillus plantarum 90 (Lp90), Lactobacillus helveticus 76 (Lh76), Lactobacillus casei 37 (Lc37), Lactobacillus paracasei 01 (Lpc01), Lactobacillus acidophilus 85 (La85) and Bifidobacterium lactis 80 (Bla80). The effects of LAB fermentation on sugars and organic acids contents, phenolic profiles, antioxidant capacity and flavor volatiles of fermented AJ (FAJ) were investigated. Results showed that AJ was an excellent food matrix for LAB strains. Lh76 and Lp90 showed the highest viable counts of 12.7 log CFU/mL at the end of fermentation. Lp90, La85 and Bla80 exhibited strong malolactic conversion capacity and finally produced lactic acid more than 6.5 mg/mL. In addtion, LAB fermentation significantly (p

Metabolic Hydrogen Flows in Rumen Fermentation: Principles and Possibilities of Interventions.

Abstract: Rumen fermentation affects ruminants productivity and the environmental impact of ruminant production. The release to the atmosphere of methane produced in the rumen is a loss of energy and a cause of climate change, and the profile of volatile fatty acids produced in the rumen affects the post-absorptive metabolism of the host animal. Rumen fermentation is shaped by intracellular and intercellular flows of metabolic hydrogen centered on the production, interspecies transfer, and incorporation of dihydrogen into competing pathways. Factors that affect the growth of methanogens and the rate of feed fermentation impact dihydrogen concentration in the rumen, which in turn controls the balance between pathways that produce and incorporate metabolic hydrogen, determining methane production and the profile of volatile fatty acids. A basic kinetic model of competition for dihydrogen is presented, and possibilities for intervention to redirect metabolic hydrogen from methanogenesis toward alternative useful electron sinks are discussed. The flows of metabolic hydrogen toward nutritionally beneficial sinks could be enhanced by adding to the rumen fermentation electron acceptors or direct fed microbials. It is proposed to screen hydrogenotrophs for dihydrogen thresholds and affinities, as well as identifying and studying microorganisms that produce and utilize intercellular electron carriers other than dihydrogen. These approaches can allow identifying potential microbial additives to compete with methanogens for metabolic hydrogen. The combination of adequate microbial additives or electron acceptors with inhibitors of methanogenesis can be effective approaches to decrease methane production and simultaneously redirect metabolic hydrogen toward end products of fermentation with a nutritional value for the host animal. The design of strategies to redirect metabolic hydrogen from methane to other sinks should be based on knowledge of the physicochemical control of rumen fermentation pathways. The application of new -omics techniques together with classical biochemistry methods and mechanistic modeling can lead to exciting developments in the understanding and manipulation of the flows of metabolic hydrogen in rumen fermentation.

A heterogeneous microbial consortium producing short-chain fatty acids from lignocellulose

Abstract: Microbial consortia are a promising alternative to monocultures of genetically modified microorganisms for complex biotransformations. We developed a versatile consortium-based strategy for the direct conversion of lignocellulose to short-chain fatty acids, which included the funneling of the lignocellulosic carbohydrates to lactate as a central intermediate in engineered food chains. A spatial niche enabled in situ cellulolytic enzyme production by an aerobic fungus next to facultative anaerobic lactic acid bacteria and the product-forming anaerobes. Clostridium tyrobutyricum, Veillonella criceti, or Megasphaera elsdenii were integrated into the lactate platform to produce 196 kilograms of butyric acid per metric ton of beechwood. The lactate platform demonstrates the benefits of mixed cultures, such as their modularity and their ability to convert complex substrates into valuable biochemicals.

Increased demand for NAD+ relative to ATP drives aerobic glycolysis

Abstract: Aerobic glycolysis, or preferential fermentation of glucose-derived pyruvate to lactate despite available oxygen, is a hallmark of proliferative metabolism that is observed across many organisms and conditions. To better understand why aerobic glycolysis is associated with cell proliferation, we examined the metabolic consequence of activating the pyruvate dehydrogenase complex (PDH) to increase mitochondrial pyruvate oxidation at the expense of fermentation. We find that increasing PDH activity impairs cell proliferation by reducing the nicotinamide adenine dinucleotide cofactor ratio (NAD+/NADH). This change in NAD+/NADH ratio is caused by an increase in mitochondrial membrane potential that impairs mitochondrial electron transport and NAD+ regeneration. Uncoupling mitochondrial respiration from ATP synthesis or increasing ATP hydrolysis restores NAD+/NADH homeostasis and proliferation even when glucose oxidation is increased. These data suggest that when the demand for NAD+ to support oxidation reactions exceeds the demand for ATP consumption in cells, NAD+ regeneration by mitochondrial respiration becomes constrained, promoting fermentation despite available oxygen. This argues that cells engage in aerobic glycolysis when the cellular demand for NAD+ is in excess of the cellular demand for ATP.

Malic acid production from renewables: A review

Abstract: Malic acid derived from fossil resources is currently applied in the food and beverage industries with a medium global production capacity. However, in the transition from a fossil‐based to a bio‐based economy, biotechnologically produced l‐malic acid may become an important platform chemical with many new applications, especially in the field of biopolymers. In this review, currently used petrochemical production routes to dl‐malic acid are outlined and insights into possible bio‐based alternatives for microbial l‐malic acid production are provided. Besides ecological reasons, the possibility to produce enantiopure l‐malic acid by microbial fermentation is the biggest advantage over chemical synthesis. State‐of‐the‐art and open challenges concerning production host engineering, substrate choice and downstream processing are addressed. With regard to production hosts, a literature overview is given covering the leading natural production strains of Aspergillus, Ustilago and Aureobasidium, as well as Escherichia coli as the most important engineered recombinant host. The utilization of renewable substrates as an alternative to glucose is emphasized in particular as a key aspect for a competitive bio‐based production. Out of the alternative substrates discussed in this review, the industrial side‐streams crude glycerol and molasses seem to be most promising for large‐scale l‐malic acid production. © 2019 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effects of different temperatures on bacterial diversity and volatile flavor compounds during the fermentation of suancai, a traditional fermented vegetable food from northeastern China

Abstract: The bacterial diversity and volatile flavor compounds (VFCs) during suancai fermentation in different temperatures were investigated by Illumina Hiseq sequencing and GC-MS. Firmicutes and Proteobacteria were observed to be the dominant phyla during the fermentation. Lactobacillus, Serratia, Leuconostoc, Pseudomonas, Pseudomonas, Pediococcus, etc., were observed as the main genus. Serratia and Pseudomonas predominated the early stage of suancai fermentation, while Lactobacillus predominated the later stage. Leuconostoc predominated the fermentation at 10 °C and 15 °C, while Weissella and Lactococcus predominated at 20 °C and 25 °C. A total of 86 VFCs were detected in all suancai samples. With the increase of the fermentation temperature, the kinds of VFCs were also increased. Lactobacillus, Pediococcus, Lactococcus, Brochothrix, Psychrobacter, Pseudoalteromonas, Acinetobacter and Enterobacter were the important bacteria related to VFCs during the fermentation. The bacteria were highly correlated with the VFCs in suancai fermentation. As the most dominant genus, Lactobacillus was significantly positive correlated with 13 VFCs. The correlation between the bacteria and VFCs in suancai could be used to search for microbial markers. In conclusion, 20 °C could accelerate the maturation and improve the sensory quality of suancai. This study could provide useful guidelines for screening of strains that contribute to the flavor formation in suancai fermentation.

Visible-light-driven amino acids production from biomass-based feedstocks over ultrathin CdS nanosheets.

Abstract: Chemical synthesis of amino acids from renewable sources is an alternative route to the current processes based on fermentation. Here, we report visible-light-driven amination of biomass-derived α-hydroxyl acids and glucose into amino acids using NH3 at 50 °C. Ultrathin CdS nanosheets are identified as an efficient and stable catalyst, exhibiting an order of magnitude higher activity towards alanine production from lactic acid compared to commercial CdS as well as CdS nanoobjects bearing other morphologies. Its unique catalytic property is attributed mainly to the preferential formation of oxygen-centered radicals to promote α-hydroxyl acids conversion to α-keto acids, and partially to the poor H2 evolution which is an undesired side reaction. Encouragingly, a number of amino acids are prepared using the current protocol, and one-pot photocatalytic conversion of glucose to alanine is also achieved. This work offers an effective catalytic system for amino acid synthesis from biomass feedstocks under mild conditions. Chemical production of amino acids from renewable carbon sources in an energy-saving manner is highly desirable. Here, the authors report visible-light-driven, CdS nanosheets-promoted synthesis of amino acids from biomass-based feedstock and NH3 under mild reaction conditions.

Functional role of yeasts, lactic acid bacteria and acetic acid bacteria in cocoa fermentation processes.

Abstract: Cured cocoa beans are obtained through a post-harvest, batchwise process of fermentation and drying carried out on farms in the equatorial zone. Fermentation of cocoa pulp-bean mass is performed mainly in heaps or boxes. It is made possible by a succession of yeast, lactic acid bacteria (LAB) and acetic acid bacteria (AAB) activities. Yeasts ferment the glucose of the cocoa pulp into ethanol, perform pectinolysis and produce flavour compounds, such as (higher) alcohols, aldehydes, organic acids and esters. LAB ferment the glucose, fructose and citric acid of the cocoa pulp into lactic acid, acetic acid, mannitol and pyruvate, generate a microbiologically stable fermentation environment, provide lactate as carbon source for the indispensable growth of AAB, and contribute to the cocoa and chocolate flavours by the production of sugar alcohols, organic acids, (higher) alcohols and aldehydes. AAB oxidize the ethanol into acetic acid, which penetrates into the bean cotyledons to prevent seed germination. Destruction of the subcellular seed structure in turn initiates enzymatic and non-enzymatic conversions inside the cocoa beans, which provides the necessary colour and flavour precursor molecules (hydrophilic peptides, hydrophobic amino acids and reducing sugars) for later roasting of the cured cocoa beans, the first step of the chocolate-making.

Lactic Acid Fermentation of Cereals and Pseudocereals: Ancient Nutritional Biotechnologies with Modern Applications

Abstract: Grains are a substantial source of macronutrients and energy for humans. Lactic acid (LA) fermentation is the oldest and most popular way to improve the functionality, nutritional value, taste, appearance and safety of cereal foods and reduce the energy required for cooking. This literature review discusses lactic acid fermentation of the most commonly used cereals and pseudocereals by examination of the microbiological and biochemical fundamentals of the process. The study provides a critical overview of the indispensable participation of lactic acid bacteria (LAB) in the production of many traditional, ethnic, ancient and modern fermented cereals and beverages, as the analysed literature covers 40 years. The results reveal that the functional aspects of LAB fermented foods are due to significant molecular changes in macronutrients during LA fermentation. Through the action of a vast microbial enzymatic pool, LAB form a broad spectrum of volatile compounds, bioactive peptides and oligosaccharides with prebiotic potential. Modern applications of this ancient bioprocess include the industrial production of probiotic sourdough, fortified pasta, cereal beverages and “boutique” pseudocereal bread. These goods are very promising in broadening the daily menu of consumers with special nutritional needs.

A Review of Selection Criteria for Starter Culture Development in the Food Fermentation Industry

Abstract: Starter cultures are defined as selected microbial preparations used to increase the efficiency of fermentation processes. In the food industry, numerous microbial cultures are used to ensure the p...

Distinct Changes of Metabolic Profile and Sensory Quality during Qingzhuan Tea Processing Revealed by LC-MS-Based Metabolomics

Abstract: Qingzhuan tea (QZT) is a unique type of dark tea exclusively produced in Hubei Province of China. In the current study, liquid chromatography-mass spectrometry (LC-MS) coupled with multivariate analysis was applied to characterize the chemical composition of QZT and investigate the effect of QZT processing on its metabolic profile and sensory quality. The contents of polyphenols and flavonoids decreased significantly while the polysaccharides content remained stable, while the theabrownin content inversely increased during QZT processing. LC-MS-based metabolomics analyses revealed that the tea sample after microbial fermentation (MFT) was dramatically different from the sample before microbial fermentation (UFT), while MFT was very similar to QZT. A total of 102 compounds were identified as critical metabolites responsible for metabolic changes caused by QZT processing, with the contents of catechins and flavonoids significantly decreased, and some novel phenolic acids and catechin derivatives were formed. The sensory quality of QZT was mainly formed during microbial fermentation, which greatly reduced the astringency and bitterness of raw tea leaves and produced its characteristic woody and stale aroma as well as mellow taste. These results suggested that microbial fermentation is the critical process in changing the metabolic profile of raw tea leaves and forming the sensory quality of QZT.

Microbial exopolysaccharides for immune enhancement: Fermentation, modifications and bioactivities

Abstract: Many microorganisms are able to synthesize polysaccharides and then secrete them into the external environment; these compounds are known as exopolysaccharides (EPS). The EPS are produced for various purposes including protection, adhesion, biofilm formation, and as a nutrient source. These polymers can be produced by microbes such as archaea, bacteria, and fungi. On an industrial scale, it is beneficial to use microbes because they can be cultivated using controlled conditions and produce a large quantity of EPS within short periods. Fermentation techniques, therefore, are important strategies that are used to improve product yield and productivity. These techniques can be done using submerged fermentation and solid-state fermentation. In addition, the application of optimization techniques are able to be used to obtain the maximum yield of microbial EPS. Some EPS (called bioactive EPS) derived from microbes show bioactivities such as anticancer, antioxidant, antimicrobial, and immunomodulatory activities. There are many factors influencing their bioactivities including their structure, molecular weight, functional groups, and monosaccharide compositions. Moreover, there are many reports where various methods have been used to modify microbial EPS to improve their bioactivities. The modification methods include biological, physical, chemical, and biomolecular modifications. Additionally, immunomodulatory EPS have been extensively studied. The immune stimulating activities of EPS have been investigated both in vitro and in vivo, and some reports have suggested possible pathways for activating the immune response. This review will focus on resources, fermentation, modification, and bioactivities of EPS, and review possible mechanisms of microbial EPS stimulating immune responses.

Enhancing CO2-Valorization Using Clostridium autoethanogenum for Sustainable Fuel and Chemicals Production

Abstract: Acetogenic bacteria can convert waste gases into fuels and chemicals. Design of bioprocesses for waste carbon valorization requires quantification of steady-state carbon flows. Here, steady-state quantification of autotrophic chemostats containing Clostridium autoethanogenum grown on CO2 and H2 revealed that captured carbon (460 ± 80 mmol/gDCW/day) had a significant distribution to ethanol (54 ± 3 C-mol% with a 2.4 ± 0.3 g/L titer). We were impressed with this initial result, but also observed limitations to biomass concentration and growth rate. Metabolic modeling predicted culture performance and indicated significant metabolic adjustments when compared to fermentation with CO as the carbon source. Moreover, modeling highlighted flux to pyruvate, and subsequently reduced ferredoxin, as a target for improving CO2 and H2 fermentation. Supplementation with a small amount of CO enabled co-utilization with CO2, and enhanced CO2 fermentation performance significantly, while maintaining an industrially relevant product profile. Additionally, the highest specific flux through the Wood-Ljungdahl pathway was observed during co-utilization of CO2 and CO. Furthermore, the addition of CO led to superior CO2-valorizing characteristics (9.7 ± 0.4 g/L ethanol with a 66 ± 2 C-mol% distribution, and 540 ± 20 mmol CO2/gDCW/day). Similar industrial processes are commercial or currently being scaled up, indicating CO-supplemented CO2 and H2 fermentation has high potential for sustainable fuel and chemical production. This work also provides a reference dataset to advance our understanding of CO2 gas fermentation, which can contribute to mitigating climate change.

A Holistic Review on Euro-Asian Lactic Acid Bacteria Fermented Cereals and Vegetables.

Abstract: Lactic acid fermentation is one of the oldest methods used worldwide to preserve cereals and vegetables. Europe and Asia have long and huge traditions in the manufacturing of lactic acid bacteria (LAB)-fermented foods. They have different cultures, religions and ethnicities with the available resources that strongly influence their food habits. Many differences and similarities exist with respect to raw substrates, products and microbes involved in the manufacture of fermented products. Many of them are produced on industrial scale with starter cultures, while others rely on spontaneous fermentation, produced homemade or in traditional events. In Europe, common LAB-fermented products made from cereals include traditional breads, leavened sweet doughs, and low and non-alcoholic cereal-based beverages, whereas among vegetable ones prevail sauerkraut, cucumber pickles and olives. In Asia, the prevailing LAB-fermented cereals include acid-leavened steamed breads or pancakes from rice and wheat, whereas LAB-fermented vegetables are more multifarious, such as kimchi, sinki, khalpi, dakguadong, jiang-gua, soidon and sauerkraut. Here, an overview of the main Euro-Asiatic LAB-fermented cereals and vegetables was proposed, underlining the relevance of fermentation as a tool for improving cereals and vegetables, and highlighting some differences and similarities among the Euro-Asiatic products. The study culminated in "omics"-based and future-oriented studies of the fermented products.