Fermentation, Volume 10, Issue 2 (February 2024) – 43 articles

This study investigated the combined impact of essential oil blends (EOBs) and fumaric acid (FA) on ruminal fermentation in dairy cows using the rumen simulation technique (RUSITEC) system. Three rumen-cannulated, non-lactating Holstein Friesian cows served as inoculum donors. The substrate, a total mixed ration (TMR), comprised corn silage, alfalfa hay, and a concentrate mix in a 3:1:1 ratio. The four treatments evaluated were Control (TMR without additives), EFA1 (TMR + EOB1 + FA), EFA2 (TMR + EOB2 + FA), and EFA3 (TMR + EOB3 + FA). Sixteen fermentation chambers were randomly assigned to the treatments, each with four replicates, following a completely randomized design during a 9-day experimental period. EOBs and FA were added at 10 µL/g feed and 3% of TMR, respectively. After a 4-day adaptation, samples were collected for 5 days. Results revealed that EFA1 significantly reduced (p = 0.0351) CH₄ emissions by 60.2% without negatively impacting dry matter disappearance, fiber fraction digestibility, pH, or gas volume. All EFAs increased (p < 0.001) the propionate molar proportion and decreased (p < 0.001) the acetate-to-propionate ratio. EFA2 decreased (p < 0.05) the acetate proportion by 3.3% compared to the control. In conclusion, EFA1 is recommended as an effective nutritional intervention to mitigate CH₄ emissions and optimize ruminal fermentation in dairy cows. Full article

Currently, industry in all its forms is vital for the human population because it provides the services and goods necessary to live. However, this process also pollutes soils and rivers. This research provides an environmentally friendly solution for the generation of electrical energy and the bioremediation of heavy metals such as arsenic, iron, and copper present in river waters used to irrigate farmers’ crops. This research used single-chamber microbial fuel cells with activated carbon and zinc electrodes as anodes and cathodes, respectively, and farmers’ irrigation water contaminated with mining waste as substrate. Pseudomonas stutzeri was used as a biocatalyst due to its ability to proliferate at temperatures between 4 and 44 °C—at which the waters that feed irrigated rivers pass on their way to the sea—managing to generate peaks of electric current and voltage of 4.35 mA and 0.91 V on the sixth day, which operated with an electrical conductivity of 222 mS/cm and a pH of 6.74. Likewise, the parameters of nitrogen, total organic carbon, carbon lost on the ignition, dissolved organic carbon, and chemical oxygen demand were reduced by 51.19%, 79.92%, 64.95%, 79.89%, 79.93%, and 86.46%. At the same time, iron, copper, and arsenic values decreased by 84.625, 14.533, and 90.831%, respectively. The internal resistance values shown were 26.355 ± 4.528 Ω with a power density of 422.054 mW/cm² with a current density of 5.766 A/cm². This research gives society, governments, and private companies an economical and easily scalable prototype capable of simultaneously generating electrical energy and removing heavy metals. Full article

2,3,5-trimethylpyrazine (TMP), as a volatile heterocyclic nitrogen compound, has a wide range of applications. To explore an efficient and environmentally friendly way to produce TMP, Bacillus strains were isolated from Daqu using traditional separation and purification methods. The fermentation products were detected by gas chromatography–mass spectrometry (GC-MS), and the species relationship of strains was analyzed by morphological and phylogenetic tree construction. Single factors were selected to optimize the fermentation process of TMP production, and a Box–Behnken design was used for response surface testing. The LC-6 strain isolated from Daqu was Bacillus amyloliquefaciens, and its fermentation products contained TMP, with a relatively high value of 0.071 ± 0.011 mg/g, indicating that the LC-6 strain was a potentially valuable TMP-producing bacterium. The results of single-factor testing showed that temperature, bottle capacity, and water addition significantly affected TMP production. Box–Behnken design and response surface analysis revealed that the order of influence on TMP yield was as follows: water addition > temperature > bottle capacity. Response surface optimization results showed that the optimal parameters for wheat medium fermentation were temperature 37 °C, bottle capacity 100 g/250 mL, and water addition 39 mL. Under these fermentation conditions, the average production of TMP was 0.446 ± 0.052 mg/g, which was 0.375 mg/g higher than that obtained before optimization. Compared with the previous period, the production of TMP indeed increased, providing a basis for further research on the solid-state fermentation process of TMP synthesis. Full article

Salt is a key ingredient that can both enhance the taste and extend the shelf life of fermented vegetables. However, it is important to note that excessive salt levels can have adverse effects on consumer health. This study aimed to investigate the impact of various salt additions (2%, 4%, 6%, 8%, and 10% wt/wt) on the flavor profile of fermented ciba pepper, a traditional Chinese fermented chili sauce, using gas chromatography–ion mobility spectrometry (GC-IMS) in combination with an electronic nose (E-nose). Fermented ciba pepper samples were prepared with different salt additions: 2% (LJA), 4% (LJB), 6% (LJC), 8% (LJD), and 10% (LJE) (wt/wt). The physicochemical and sensory properties of the fermented ciba pepper samples were evaluated. Sensory evaluation indicated that LJC and LJD received higher scores compared to the other groups. The total acid and amino acid nitrogen contents displayed contrasting trends with the salt additions (p < 0.05). The E-nose analysis successfully differentiated the flavor profiles of the ciba pepper samples fermented with varying salt additions. Additionally, the GC-IMS analysis identified a total of 72 volatile compounds, including 14 alcohols, 21 esters, nine aldehydes, four acids, eight ketones, three terpenes, and eight other substances. Notably, the ciba pepper samples with lower salt additions exhibited higher levels of alcohols, aldehydes, and esters. In conclusion, the addition of salt during the fermentation process significantly influenced the formation of flavor compounds in ciba pepper. This study provides valuable insights into ciba pepper fermentation with different salt additions and offers prospects for the development of low-salt fermented ciba pepper products. Full article

Few studies have evaluated the impact of a lipid-rich diet with palmitic acid (PA) in ruminal fermentation. The objective was to evaluate the in vitro bath culture of the protected PA on the ruminal fermentative variables. Four diets were used: (a) without protected PA (nPA) and (b) inclusion of protected PA at three levels: PA3 = 3%, PA6 = 6%, and PA9 = 9% dry matter (DM). The maximum gas production occurred without including protected PA and the low gas production given with the inclusion of protected PA9 (p ≤ 0.05). Meanwhile, the inclusion with 3 and 6% of protected PA showed a higher level of gas production kinetics than the other treatments (p ≤ 0.05). DM and organic matter degradation after 72 h of incubation linearly decreased (p ≤ 0.05) with a high level of protected PA. The level of C16:0 in the protected AP increased with the higher level of supplemented AP (p ≤ 0.05). The best efficiency in propionic acid, decrease in methane, and increase in biohydrogenation (79%) occurred with the inclusion of protected PA3 (p ≤ 0.05). In conclusion, supplements with protected PA at 3 and 6% increased PA availability. The results indicate good benefits of protected PA on fermentative variables, and these doses seem ideal for future research in lactating goats. Full article

Microbial electrochemical systems have shown great value as a means of enhancing the efficiency of fermentation reactions, but at present, there is no reliable means to balance the extracellular electron supply and corresponding intracellular demands in these systems. The current work describes the unique use of an oxidation–reduction-potential (ORP)-level-controlled microbial electrolysis cell (MEC) system to successfully balance the extracellular electron supply and succinic acid fermentation via A. succinogenes (130Z). The ORP-controlled MEC system with neutral red (NR) yielded a significant increase in succinic acid production (17.21%). The utilization of NR in this MEC system improved the ORP regulatory sensitivity. The optimal approach to the ORP level control was the use of a −400 mV high-voltage electric pulse-based strategy, which increased the yield of succinic acid by 13.08% compared to the control group, and reduced the energy consumption to 52.29% compared to the potentiostatic method. When compared to the −1 V constant potential MEC system, the high-voltage electric pulse-based ORP strategy for the MEC system control provided sufficient electrons to this system while using less electricity (11.96%) and producing 12.48% (74.43 g/L) more succinic acid during fed-batch fermentation. The electronic utilization efficiency of the ORP-controlled MEC system was 192.02%, which was 15.19 times that of the potentiostatic system. The electronic utilization efficiency is significantly increased in the ORP-controlled MEC system. Succinic acid production is ensured by a high-voltage electric pulse-based method, while the influence on cell growth and power consumption are minimized. Fed-batch fermentation with the high-voltage electric pulse-based ORP strategy for MEC system control is noted to be ideal to achieve a further increase in succinic acid concentration and electronic utilization efficiency. Full article

Background: This study aimed to investigate the impact of in vitro rumen fermentation (IVRF) on the microbiome structure and composition of rumen fluid before and after fermentation assays. Methods and Results: Six separate fermentation batches were run for 48 h using maize silage as the basal feed. Rumen fluid samples were analyzed before (RF; only rumen fluid inoculant) and after 48 h fermentation assay (MS; maize silage as the substrate) and further processed for microbiome analysis using amplicon sequencing targeting the V4 region of the bacterial 16S rRNA gene. Bacterial alpha diversity revealed that the Shannon index and observed index were similar between MS and RF fluid. The core microbiome was detected in 88.6% of the amplicon sequence variants in MS and RF. Taxonomic analysis at the phylum level showed similar abundances of Bacteroidetes, Proteobacteria, Firmicutes, Verrucomicrobiota, Spirochaetota, Patescibacteria, and Campilobacterota in MS and RF. The Bray–Curtis distance matrix showed similar bacterial community structure among MS and RF samples. Conclusion: Our results indicated that the in vitro procedure did not affect the bacterial community structure compared to the original rumen fluid inoculum. It should be noted that assessing the microbiome at a single endpoint (i.e., 48 h) may not provide a comprehensive understanding of the microbiome profile dynamics. However, the findings of this study provide a basis for future microbiome-based in vitro fermentation tests and confirm that the technique allows a high degree of species diversity that approximates the rumen function in vivo. Full article

Enzymatic solid-state fermentation can improve the nutritional quality of feed materials. The current study aimed to determine the effect of the solid-state fermentation of rapeseed meal (RSM) with carbohydrase/s and phytases in various combinations. RSM was fermented for 24 h at 25 °C with eight commercial preparations and mixtures thereof to prepare eleven products (PHYL—liquid-6-phytase; RON NP—6-phytase; RON HI—6-phytase; RON R—α-amylase; RON WX—β-xylanase; RON VP—β-glucanase; RON A—α-amylase, β-glucanase; RON M—xylanase, β-glucanase; RON NP+M; RON NP+A; RON NP+M+R). Afterward, the enzymes were deactivated at 70 °C within 15 min, and the biomass was dried for 24 h at 55 °C. Carbohydrase and/or phytase additives did not positively affect crude or true protein content or reduce crude fiber (p > 0.05). Among the products after fermentation, a significant reduction in the content of the raffinose family oligosaccharides, glucosinolates, and phytate was found. In the presence of phytase, the phytate reduction was more significant (p < 0.01) than that in the presence of carbohydrases only. The addition of carbohydrases together with phytases did not improve the results in comparison with phytases alone (p > 0.05). The most valuable effect was found for liquid-6-phytase (PHYL). Full article

Lutein, a yellow xanthophyll carotenoid, is increasingly recognized for its nutraceutical benefits, particularly in protecting the retina’s macula from age-related degeneration. Microalgae are a promising source of lutein, which can be a primary product or a coproduct in biorefineries. Certain microalgae exhibit lutein levels (up to 1.7%) surpassing those of common dietary sources like kale, spinach, and egg yolk (approximately 0.7–0.9%). Predominantly associated with photosystem II’s light-harvesting complex, lutein is crucial in photosynthesis and cellular defense. However, being quantitatively minor among cellular constituents, lutein necessitates specialized processing for efficient extraction. Although ubiquitous in microalgae, it is not as easily inducible as β-carotene and astaxanthin in Dunaliella salina and Haematococcus pluvialis, respectively. Currently, microalgal lutein production predominantly occurs at the bench scale, presenting challenges in scaling up. Factors like culture medium significantly influence biomass and lutein yields in industrial production, while downstream processing requires cost-effective, food-grade solvent extraction techniques. This review delves into contemporary methods and innovative progress in microalgal lutein production, emphasizing industrial-scale processes from biomass cultivation to final product formulation. A conceptual industrial process proposed in this review shows that two 10 m³ photobioreactors could produce 108 kg dry mass for Chlorella minutissima, which can be processed into approximately 616 g of lutein extract, or over 6000 capsules of finished nutraceutical daily. Despite lutein production via microalgae being in nascent stages at large scales, existing research provides a solid foundation for well-informed scale-up endeavors. Full article

This study aimed to develop bioactive bi-layer edible films based on starch (primary layer) and LAB-fermented whey and/or mango pulp powder solutions (secondary layer). Bioactive bi-layer edible films were evaluated for their physical properties, mechanical properties, antioxidant capacity, and Lactobacillus rhamnosus availability for 28 days (4 and 20 °C). Selected bioactive bi-layer edible film was applied to sushi to evaluate its sensory acceptance. The results indicated that bi-layer edible films based on LAB-fermented whey/mango solutions presented a higher quantity of phenolic compounds (95.87–107.67 mg GAE/100 g) and higher antioxidant capacity (74.84–77.64%). In addition, the higher viability (10⁶–10⁷ CFU/g) of L. rhamnosus after edible film production was obtained in those formulated with whey. After the storage period, the antioxidant capacity of all edible films was significantly affected by the storage time, while edible films containing whey in their formulation and stored at 4 °C had a L. rhamnosus count higher than 6 log cycles, which is the minimum required threshold to exert its beneficial effects in humans. The sushi covered with the selected bi-layer edible film was well accepted by the consumers, showing acceptance values between “I like it” and “I like it much”. Therefore, the developed bi-layer edible films can serve as an alternative for adding health-promoting compounds to sushi with an adequate sensory acceptance of the consumers. Full article

E2-Spy (abbreviated as ES) plays a vital role as a component in the Bacterial-Like Particles (BLPs) vaccine against classical swine fever virus (CSFV). This vaccine demonstrates remarkable immunoprotection, highlighting the importance of augmenting ES production in the development of CSFV subunit vaccines. In this study, a Pichia pastoris strain capable of high-yield secretory production of ES was developed through signal peptide engineering, gene dosage optimization and co-expression of molecular chaperones. Initially, a hybrid signal peptide cSP3 was engineered, leading to a 3.38-fold increase in ES production when compared to the control strain 1-α-ES. Subsequently, cSP3 was evaluated for its expression efficiency alongside different commonly used signal peptides under multicopy conditions. SDS-PAGE analysis revealed that 2-αd14-ES exhibited the highest ES production, displaying a 4.38-fold increase in comparison to 1-α-ES. Afterwards, SSA1, YDJ1, BIP, LHS1, and their combinations were integrated into 2-αd14-ES, resulting in a 1.92-fold rise in ES production compared to 2-αd14-ES (equivalent to a 6.18-fold increase compared to 1-α-ES). The final yield of ES was evaluated as 168.3 mg/L through comparison with serially diluted BSA protein bands. Full article

This study examined the safety of meat products from north Serbia (Vojvodina), smoked in traditional conditions, from a PAH point of view, and assessed the possibility of their reduction in these types of products. Samples of dry cured meat products, bacons and dry fermented sausages smoked in six different chambers on the territory of Vojvodina were examined. The contents of 16 polycyclic aromatic hydrocarbons, from the United States Environmental Protection Agency list (16 US-EPA PAHs), and sensory quality of meat products were determined. The total content of 16 US-EPA PAHs in dry cured meat products was in the range from 99.73 μg/kg to 412.76 μg/kg; in bacons it was in the range from 36.43 μg/kg to 188.86 μg/kg; and in dry fermented sausages in the range from 47.23 μg/kg to 270.60 μg/kg. The lowest contents of 16 US-EPA PAHs compounds were determined in meat products smoked in traditional conditions during 3–5 days (3–4 h per day) at a distance of 2.5 m between the fire and products. Generally, it can be concluded that shortening of smoking process is justified, because products of good sensory quality and with decreased content of PAHs compounds were obtained. Benzo[a]pyrene, whose maximum allowed content in smoked meat products is 2 μg/kg, was below the limit of detection in all examined traditional meat products from Vojvodina. Also, contents of PAH4, sum of benz[a]anthracene, chrysene, benzo[a]pyrene and benzo[b]fluoranthene, were in the range from ND to 2.22 μg/kg, still greatly lower than the set maximum value. These results indicated the safety of dry cured meat products, bacons and dry fermented sausages from the territory of north Serbia (Vojvodina), as defined by EU Regulation 2023/915 criteria for PAHs contents. Full article

This study addresses the production enhancement of pullulan, an extracellular polysaccharide with various applications. Pullulan is primarily produced by Aureobasidium pullulans (A. pullulans), and genetic modification is commonly used to increase its yield. However, there is a need for a more efficient and safer method. To achieve this, we designed a high-throughput screening system utilizing a unique fluorescent protein specific to pullulan. Ultraviolet (UV) mutagenesis was applied to create a pool of mutant strains, and flow cytometry allowed for single-cell screening. Our approach yielded strain M1-B3, which exhibited a substantial increase in pullulan production from 26.5 g/L to 76.88 g/L. Additionally, the molecular weight of the produced pullulan significantly increased, expanding its potential commercial application. This study demonstrates an efficient and safe method to enhance pullulan production in A. pullulans. The UV mutagenesis and flow cytometry based on screening not only increased yield but also improved pullulan’s molecular weight. The adaptability of this method to other polysaccharides and its potential for genomic analysis and broader applications make it a valuable tool in bioproduction. Full article

Providing simultaneously autotrophic and heterotrophic carbon sources is a promising strategy to overcome the limits of autotrophic syngas fermentations. D-xylose and L-arabinose are particularly interesting as they can be obtained by the hydrolysis of lignocellulosic biomass. The individual conversion of varying initial concentrations of these pentoses and D-fructose as reference was studied with C. autoethanogenum in fully controlled stirred-tank reactors with a continuous syngas supply. All mixotrophic batch processes showed increased biomass and product formation compared to an autotrophic reference process. Simultaneous CO and D-xylose or L-arabinose conversion was observed in contrast to D-fructose. In the mixotrophic batch processes with L-arabinose or D-xylose, the simultaneous CO and sugar conversion resulted in high final alcohol-to-acid ratios of up to 58 g g⁻¹. L-arabinose was superior as a mixotrophic carbon source because biomass and alcohol concentrations (ethanol and 2,3-butanediol) were highest, and significant amounts of meso-2,3-butanediol (>1 g L⁻¹) in addition to D-2,3-butanediol (>2 g L⁻¹) were solely produced with L-arabinose. Furthermore, C. autoethanogenum could not produce meso-2,3 butanediol under purely heterotrophic conditions. The mixotrophic production of meso-2,3-butanediol from L-arabinose and syngas, both available from residual lignocellulosic biomass, is very promising for use as a monomer for bio-based polyurethanes or as an antiseptic agent. Full article

Lactic acid is widely used in the food industry. It can be produced via chemical synthesis or biotechnological pathways by using renewable resources as substrates. The main challenge of sustainable production lies in reaching productivities and yields that allow for their industrial production. In this case, the application of process engineering becomes a crucial tool to improve the performance of bioprocesses. In this work, we performed the solid-state fermentation of grape stalk using Rhizopus oryzae NCIM 1299 to obtain lactic acid, employing three different temperatures (22, 35, and 40 °C) and a relative humidity of 50%. The Logistic and First-Order Plus Dead Time models were adjusted for fungal biomass growth, and the Luedeking and Piret with Delay Time model was used for lactic acid production, obtaining higher R² values in all cases. At 40 °C, it was observed that Rhizopus oryzae grew in pellet form, resulting in an increase in lactic acid productivity. In this context, the effect of temperature on the kinetic parameters was evaluated with a polynomial correlation. Finally, using this correlation, a smooth and continuous optimal temperature profile was obtained by a dynamic optimization method, improving the final lactic acid concentration by 53%. Full article

Bacterial cellulose (BC) is a pure exocellular polysaccharide produced by micro-organisms. It has several properties in comparison with plant-derived cellulose that make it perfectly suitable for many applications, ranging from the food industry to the biomedical area. Different production methods and modification or functionalization procedures have been investigated in response to the many possible attractive applications of BC. This review overviews the different fermentation techniques and functionalization methods together with the main possible biotechnological applications of BC for food industry and biomedical purposes. Full article

As methane fermentation is inhibited by ammonia derived from organic waste, anaerobic microbial communities tolerant to enriched wastewater with high concentrations of ammonia and salt must be obtained for methane fermentation. Therefore, acclimation cultures were prepared in bottles for 60–80 weeks with artificial wastewater medium added every 2 weeks, using three types of sludge from wastewater treatment plants in food factories. These cultures were maintained without substantially decreasing methanogenesis and gradually increasing NH₄-N and salt concentrations to 5 and 34 g/L, respectively, via the accumulation of ammonia and salt through anaerobic digestion and direct addition. The culture did not show the severe inhibition of methanogenesis or the accumulation of volatile fatty acids (VFAs) such as acetic and propionic acids. The analysis of bacterial consortia in the acclimated sludge based on the 16S rRNA sequence showed that hydrogenotrophic methanogenic bacteria of the genus Methanoculleus were dominant among archaea, whereas bacteria from the orders Clostridiales and Bacteroidales were dominant among eubacteria. Further, VFA-assimilating bacteria, including synthetic acetate-oxidizing bacteria coupled with hydrogenotrophic Methanoculleus to convert methane from acetate, were present to prevent the excessive accumulation of VFAs in the acclimation culture. The proposed acclimation process can enhance the anaerobic digestion of wastewater for methane production. Full article

Proteases are important enzymes because of their extended uses in several industries, such as food, beverages, pharmacy, detergents, and many others. Aspergillus is one of the most used fungi strains for enzyme production by solid-state fermentation (SSF). Disponibility of the carbon source is a key factor for protease production. In addition, the selection of solid support has great importance, as it must provide suitable airflow through the packed bed and nutrient diffusion inside the fermentable mass. Six Aspergillus strains and two inert supports (Agrolite (AL) and Polyurethane (PUF)) were tested for protease production from fish flour (FF) at different glucose concentrations (0, 5, 10, 15%) by SSF. The FF/PUF mixture at 70/30 (w/w) ratio, with 75.39% moisture, and a critical moisture point of 0.11 gH₂O/g, presented a texture that allowed heat and mass transfer and provided enough moisture to make free water available as required for microorganism growth during the fermentation process. Aspergillus oryzae 2095 produced higher amounts of neutral and alkaline proteases with the addition of 5% glucose to the growth medium. Kinetics studies reveal that protease production is partially associated with growth. The extracts obtained can be used in different industries, and especially to prepare fish high-value by-product hydrolysates. Full article

Pennycress (Thlaspi arvense L.) is an annual cover crop known for its exceptional cold tolerance and high oil and protein yields. Pennycress can be integrated into a corn–soybean rotation in the U.S. However, the utilization of pennycress biomass remains largely unexplored, including assessing compositional changes through its growth and organic matter digestibility. This study harvested pennycress at three growth stages, characterized the biomass for anaerobic digestion (AD), and tested the effects of concurrent alkali pretreatment and ensiling on the biomass methane yield. Results showed that the biomass harvested when the plants were undergoing senescence (“third-harvest”) had higher contents of acid detergent fiber, neutral detergent fiber, and lignin, while the biomass harvested when 80–90% of the pods were fully-sized (“second-harvest”) had the highest protein content. The AD experiments showed that the first-harvest biomass (90% of flowers opened) failed to produce biogas due to a drop in the pH and alkalinity, the second-harvest biomass was inhibited for methane production (45.74 ± 0.20 L/kg-VS), and the third-harvest biomass had a methane yield of 171.80 ± 4.82 L/kg-VS. After the alkali pretreatment and ensiling, a methane yield of 270.4 ± 3.10 L/kg-VS was obtained from the second-harvest biomass, representing a significant 4.5-fold increase (adjusted for the organic matter loss) relative to the untreated second-harvest biomass. Full article

This study aims to investigate the effect of methionine analogue 2-hydroxy-4-methylthiobutanoic acid isopropyl ester (HMBi) on the rumen microbial community, microbial carbohydrate-active enzymes (CAZy), and protein metabolism pathways in yak. Twenty-four male Maiwa yaks (252.79 ± 15.95 kg) were selected and randomly divided into groups that received the basal diet alone, or a diet supplemented with different amounts of HMBi (5 g, 10 g or 15 g). At the phylum level, the group receiving 5 g of HMBi showed a considerably higher relative abundance of Lentisphaerae than the other treatment groups (p < 0.05). The relative abundance of Actinobacteria decreased linearly with the increase in HMBi supplemental levels (p < 0.05). The relative abundance of Prevotella increased linearly with the increasing level of HMBi supplementation (p < 0.05). The relative abundance of Butyrivibrio linearly decreased (p < 0.05), and the relative abundance of Alistipes tended to linearly decrease (p = 0.084). The addition of HMBi had linear or quadratic effects on the relative abundance of CAZy enzymes and functional proteins in the rumen of yak (p < 0.05). Conclusively, these results indicated that feeding yaks a diet supplemented with HMBi is an excellent strategy to enhance carbohydrate breakdown, and improve rumen microbial structure and function. Full article

Oxidoreductase (OXR) enzymes are in high demand for biocatalytic applications in the food industry and cosmetics (glucose oxidase (GOx) and cellobiose dehydrogenase (CDH)), bioremediations (horseradish peroxidase (HRP) and laccase (LAC)), and medicine for biosensors and miniature biofuel cells (GOx, CDH, LAC, and HRP). They can be used in a soluble form and/or within the yeast cell walls expressed as chimeras on the surface of yeast cells (YSD), such as P. pastoris and S. cerevisiae. However, most of the current studies suffer from either low yield for soluble enzyme expression or low enzyme activity when expressed as chimeric proteins using YSD. This is always the case in studies dealing with the heterologous expression of oxidoreductase enzymes, since there is a requirement not only for multiple OXR gene integrations into the yeast genome (super transformations), and codon optimization, but also very careful design of fermentation media composition and fermentation conditions during expression due to the need for transition metals (copper and iron) and metabolic precursors of FAD and heme. Therefore, scientists are still trying to find the optimal formula using the above-mentioned approaches; most recently, researcher started using protein engineering and directed evolution to increase in the yield of recombinant enzyme production. In this review article, we will cover all the current state-of-the-art technologies and most recent advances in the field that yielded a high expression level for some of these enzymes in specially designed expression/fermentation systems. We will also tackle and discuss new possibilities for further increases in fermentation yield using cutting-edge technologies such as directed evolution, protein and strain engineering, high-throughput screening methods based on in vitro compartmentalization, flow cytometry, and microfluidics. Full article

Nitrites are universally acknowledged natural toxic substances that frequently lead to poisoning in humans and animals. During fermentation, certain microorganisms utilize a portion of the nitrogen element and reduce nitrates to nitrites through specific metabolic pathways. In this study, a highly effective lactic acid bacterial strain, Lactiplantibacillus plantarum A50, was isolated and screened from alfalfa silage for its remarkable ability to degrade nitrites. L. plantarum A50 exhibits exceptional nitrite removal capacity, with a degradation rate of 99.06% within 24 h. Furthermore, L. plantarum A50 demonstrates normal growth under pH values ranging from 4 to 9 and salt concentrations of 5%, displaying excellent tolerance to acidity, alkalinity, and salinity. Additionally, it undergoes fermentation using various carbon sources. Within the first 6–12 h of culture, L. plantarum A50 primarily achieves nitrite degradation through non-acidic processes, resulting in a degradation rate of 82.67% by the 12th hour. Moreover, the metabolites produced by L. plantarum A50 exhibit a synergistic interaction with acidity, leading to a nitrite degradation rate of 98.48% within 24 h. Notably, both L. plantarum A50 and MRS broth were found to degrade nitrites. Consequently, a non-targeted metabolomic analysis using LC-MS was conducted to identify 342 significantly different metabolites between L. plantarum A50 and MRS broth. Among these, lipids and lipid-like molecules, organic acids and derivatives, organic oxygen compounds, and organoheterocyclic compounds emerged as the main constituents. Lipids and lipid-like molecules, derivatives of glucose and galactose, amino acids and their derivatives, as well as organoheterocyclic compounds, are likely to play a role in nitrite elimination. Through the enrichment analysis of differential metabolic pathways using KEGG, nine distinct pathways were identified. These pathways provide essential nutrients, maintain cellular structure and function, participate in substance transport, regulate metabolic activities, and enhance resistance against pathogenic microorganisms in L. plantarum A50. Full article

In order to promote the consumption and application of cassava in the food industry, the cassava–acerola cherry juice beverage was developed using lactic acid bacteria fermentation, which improved the flavor attraction and nutritional value, increased the added value of cassava and acerola cherry. The study investigated the effects of both pure and mixed fermentation using Lactobacillus plantarum (L. plantarum) HNC7 on the chemical compounds and antioxidant activities in cassava–acerola cherry juice. Following 72 h of fermentation, the fruit juice showed increased acidity, a decrease in pH, and higher consumption of soluble solids, and a significant rise in volatile substance content and antioxidant activity (p < 0.05). Notably, the HNC7-YLC92 binary combination demonstrated the most effective fermentation, resulting in a product with uniform color, moderate sourness and sweetness, and a delicate and smooth taste. Overall, the HNC7-YLC92 binary combination, due to its beneficial biological properties, shows great potential as the optimal strain for fermenting this juice. This provides a reference for selecting industrial fermentation conditions and strains, aiming to develop new value-added cassava products and increase their consumption. Full article

Since ancient times, the placenta has been used to produce cosmetic and health food products, whereas fermentation is a technology that has been used to produce foods and cosmetics. For application in cosmetics, traditional placental extracts produced solely by proteolysis have not had enough moisturizing properties or the ability to stimulate the proliferation of epidermal keratinocytes. We combined these two traditional approaches to produce raw materials without such drawbacks that are suitable for cosmetic applications. Using a unique lactic acid bacterial strain, Enterococcus faecalis PR31, to directly ferment and digest both porcine and equine placentas, we produced the following liquid products: placenta ferment filtrates. The ferment filtrates stimulated the proliferation of not only normal human dermal fibroblasts but also epidermal keratinocytes. The ferments had higher equilibrium water content properties than traditional placental extracts, and the ferment derived from the porcine placenta maintained high stratum corneum water content levels for up to 6 h after its application on the skin. Metabolome analysis revealed various molecules that were increased by fermentation, among which lactic acid was assumed to play a central role in the high moisturizing properties. To conclude, the placenta ferment filtrates developed in this study are beneficial for cosmetic applications. Full article

Organic solid waste is a renewable resource as it can be transformed into a valuable product through various technologies. Composting is considered to be the most economical and effective technology for treating organic solid waste, but excessive amounts of heavy metals in organic solid waste compost are harmful to the environment. The current focus is on the addition of heavy metal passivators to organic solid waste to reduce the mobility and biotoxicity of heavy metals in situ or ex situ. The aims of this paper are to provide an overview of heavy metal passivators and their passivation mechanisms in the field of organic solid waste composting and to provide a reference for research on the control of heavy metal pollution in the treatment of organic solid waste. Full article

To assess the probiotic potential of strain 68-1 with rutin conversion capabilities, isolated from Chinese traditional Jiangshui, a complete genomic analysis and in vitro tests were conducted. The Oxford Nanopore Technologies (ONT, Oxford, UK)–Illumina (San Diego, CA, USA) hybrid sequencing platform was used for whole genome sequencing and the results showed that strain 68-1 had a chromosome sequence of 3,482,151 bp, with 46.53% GC content and five plasmids with a sequence length ranging from 2009 bp to 48,711 bp. Strain 68-1 was identified as Lactiplantibacillus pentosus based on the whole genome sequence. A total of 133 genes encoding for carbohydrate-active enzymes (CAZymes) were identified and genes that may be involved in rutin conversion were found in the L. pentosus 68-1 genome. L. pentosus 68-1 showed excellent tolerance to gastrointestinal juice and adhesion properties, and corresponding genes were identified. In addition, L. pentosus 68-1 exhibited strong antibacterial and antifungal activity, where organic acids may play a crucial role in its antagonistic ability. Moreover, the gene cluster for plantaricin_EF production was detected. No high virulence factor was found in the L. pentosus 68-1 genome and no hemolytic effect was observed. In addition, L. pentosus 68-1 showed resistance to ampicillin, gentamycin, and kanamycin, and the genomic analysis indicated that horizontal ARG transfer should not be possible. The results show that L. pentosus 68-1 could be developed as a novel probiotic candidate to improve rutin bioavailability in the food and feed industry. Full article

Biodiesel produced from waste cooking oil (WCO) is on the rise and inevitably leads to issues in managing glycerol waste. Due to the presence of colour, odour and other minor compounds, the refining costs for this type of glycerol are higher and uneconomical. The potential of biodiesel-derived glycerol waste (BDGW) obtained from WCO to produce the highly added product of docosahexaenoic acid (DHA), also known as omega-3 polyunsaturated fatty acid, via the marine microalga of Schizochytrium limacinum ATCC MYA-1381 under aerobic batch fermentation was investigated. Cell growth, as well as DHA production, were performed under various operating conditions, including aeration rates and BDGW concentrations. The effect of the substrate type on cell growth and DHA yield was evaluated. The optimum operating condition was obtained when the air flow of a 0.25 vvm and 50 g/L of the glycerol concentration was fed into the fermenter and maximum cell dry weight (11.40 g/L) and DHA yield (665.52 mg/g) were achieved. However, cell growth and DHA yield were not significantly different when S. limacinum was grown using various carbon sources. Successfully, it clearly demonstrates that the BDGW can be used as a cheap carbon source for DHA production via marine microalgae using aerobic batch fermentation. Full article

Prodigiosin (PG) is a secondary metabolite produced by Serratia marcescens which has a promising future in food, textile, and other industries due to its bright color and diverse biological activities. Currently, the production of PG is mainly restricted by the components of the fermentation medium and large losses during its extraction process, making large-scale industrial production impossible. In this study, a Box–Behnken design (BBD) was used to optimize the response surface of the fermentation medium of S. marcescens. The optimum medium composition was found to be sucrose, 16.29 g/L; peptone, 11.76 g/L; and tween 80, 2.64 g/L. This composition produced a PG amount of 1653.95 ± 32.12 mg/L, which is a 64-fold increase compared to the initial medium. A Box–Behnken design (BBD) was then used to optimize the response surface of the extraction process of PG, aiming to reduce loss during extraction. The optimal extraction conditions were determined to be a solvent fermentation liquid ratio of 9.12:1, an extraction temperature of 25.35 °C, and an extraction time of 30.33 min. These conditions resulted in a final PG production amount of 2142.75 ± 12.55 mg/L, which was nearly 84 times higher than the initial production amount of PG. These results provide essential theoretical and experimental support for the industrial production of PG. Full article