Mixed Microbial Culture Research Articles

Effect of Operational Conditions on the Behaviour and Associated Costs of Mixed Microbial Cultures for PHA Production.

Massive production and disposal of petrochemical derived plastics represent relevant environmental problems. Polyhydroxyalkanoates (PHA) are a renewable alternative that can even be produced from wastes. The production of PHA from acetate using mixed microbial cultures was studied. The effect of two key operational conditions was evaluated, i.e., substrate concentration and cycle length. The effects of these factors on several responses were studied using a surface response methodology. Several reactors were operated under selected conditions for at least 10 solids retention times to ensure stable operation. Results show that conditions providing higher PHA content involve lower biomass productivities. This has a great impact on biomass production costs. Results suggest then that PHA content alone may not be a reasonable criterion for determining optimal conditions for PHB production. If production costs need to be reduced, conditions that provide a lower PHA content in the selection reactor, but a higher biomass productivity may be of interest.

Biological hydrogen gas production from gelatinaceous wastewater via stand-alone circular dark/photo baffled fermenter

The novel lab-scale stand-alone circular dark/photo baffled reactor (SCBR) was developed for the treatment of synthetic gelatinaceous wastewater and the enhancement of biohydrogen production (H2) using mixed microbial culture. The pilot system was operated at a constant hydraulic retention time (HRT) of 48 h with an organic loading rate of 1.3 gCOD/L/day and pH value of 6.5 ± 0.2. The results showed that the SCBR which consists of four compartments (C1, C2, C3, and C4) was efficient for the removal of chemical oxygen demand (COD). The total COD removal efficiency was recorded to be 78 ± 13% and the production rate of H2 was enhanced. The total HPR of SCBR was 14 ± 0.7 L/day. The results revealed that the production rate of volatile fatty acids (VFAs) by dark fermentation was much higher than the consumption rate by photofermentation, and VFAs production did not inhibit the H2 production or the treatment performance of SCBR.

Consistent production of high quality PHA using activated sludge harvested from full scale municipal wastewater treatment - PHARIO.

Production of polyhydroxyalkanoate (PHA) biopolymers by mixed microbial cultures concurrent to wastewater treatment is a valorization route for residual organic material. This development has been at pilot scale since 2011 using industrial and municipal organic residuals. Previous experience was the basis for a PHA production demonstration project: PHARIO. PHARIO was centred on processing surplus activated sludge biomass from the Bath full-scale municipal wastewater treatment plant in the Netherlands to produce PHA. Full-scale surplus activated sludge was fed to a pilot facility to produce PHA rich biomass using fermented volatile fatty acid (VFA) rich liquors from industry or primary sludge sources. A PHA rich biomass with on average 0.41 gPHA/gVSS was obtained with reproducible thermal properties and high thermal stability. A routine kilogram scale production was established over 10 months and the polymer material properties and market potential were evaluated. Surplus full-scale activated sludge, over four seasons of operations, was a reliable raw material to consistently and predictably produce commercial quality grades of PHA. Polymer type and properties were systematic functions of the mean co-polymer content. The mean co-polymer content was predictably determined by the fermented feedstock composition. PHARIO polymers were estimated to have a significantly lower environmental impact compared to currently available (bio)plastics.

Agroindustrial Wastewater Treatment with Simultaneous Biodiesel Production in Attached Growth Systems Using a Mixed Microbial Culture

The use of cyanobacteria in biological wastewater treatment technologies can greatly reduce operation costs by combining wastewater bioremediation and production of lipid suitable as biodiesel feedstock. In this work, an attached growth system was employed to achieve the above-mentioned dual objective using a mixed microbial culture dominated by Leptolyngbya and Limnothrix species in diverse heterotrophic consortia. Kinetic experiments on different initial pollutant concentrations were carried out to determine the ability of the established culture to remove organic load (expressed by d-COD, dissolved-Chemical Oxygen Demand), N and P from agroindustrial wastewaters (dairy, winery and raisin). Biomass and oil productivity were determined. It was found that significant removal rates of nutrients were achieved in all the wastewaters examined, especially in that originated from winery in which the highest d-COD removal rate (up to 97.4%) was observed. The attached microbial biomass produced in winery wastewater contained 23.2% lipid/biomass, wt/wt, which was satisfying. The growth in the dairy wastewater yielded the highest attached biomass productivity (5.03 g m−2 day−1) followed by the mixed effluent of winery-raisin (4.12 g m−2 day−1) and the winery wastewater (3.08 g m−2 day−1). The produced microbial lipids contained high percentages of saturated and mono-unsaturated fatty acids (over 89% in total lipids) in all substrates examined. We conclude that the proposed attached growth photobioreactor system can be considered an effective wastewater treatment system that simultaneously produces microbial lipids suitable as biodiesel feedstock.

PHA accumulation of a mixed microbial culture co-exists with ammonia partial nitritation

The nitrifying activity in mixed cultures enriched to accumulate polyhydroxyalkanoates (PHA) is in general inhibited by the addition of chemicals, such as allylthiourea (ATU). In the present study, a sequencing batch reactor was inoculated with a mixed microbial culture enriched in PHA-accumulating microorganisms, operating under complete aerobic conditions, feast/famine regime and with ATU addition. Genera Comamonas, Azoarcus and Thauera, all of them known as PHA-accumulating bacteria, were the dominant microbial populations present in the mixed culture. They showed a PHA storage capacity up to 60.0 wt%, as hydroxybutyrate (HB) and hydroxyvalerate (HV), in a HB:HV ratio of 63:37. After 20 days of operation, ATU addition was stopped and the reactor was run under the same operational conditions for 400 days. The development of partial nitritation activity (ammonia oxidation to nitrite) was observed, presumably due to free ammonia inhibition or the selected sludge retention time. Ammonium oxidizing bacteria (AOB) from genera Nitrosomonas, Nitrosococcus and Nitrosospira were detected, whereas the composition of the dominant PHA-accumulating microbial populations was the same as in the inoculum. This enriched mixed culture reached a maximum PHA accumulation of 59.2 wt%, with a HB:HV ratio of 59:41. Results showed the simultaneous occurrence of partial nitritation and the enrichment in PHA-accumulating microorganisms, which did not affect the maximum PHA storage capacity of the system.

Bio-electrodegradation of 2,4,6-Trichlorophenol by mixed microbial culture in dual chambered microbial fuel cells

2,4,6-Trichlorophenol (TCP) was bioelectrochemically treated in anodic and cathodic compartments of two identical dual chambered microbial fuel cells MFC-A and MFC-B under anaerobic and aerobic conditions, respectively, and energy was recovered in the form of electricity. It was observed that MFC-B with bio-cathodic treatment of TCP outcompeted the MFC-A with bio-anodic treatment. The maximum power density for MFC-A with bio-anode was found to be 446.76mW/m2 while for MFC-B with bio-cathode it was 1059.58mW/m2. The MFC-B consistently showed higher coulombic efficiency, power density and chemical oxygen demand removal efficiency indicating the better performance of the MFC-B as compared to the MFC-A. Scanning electron micrograph also confirmed better accumulation of microbes on the anode of MFC-B and hence its better performance in terms of energy recovery. Some major genera present in the microbial community were quantified using quantitative real-time polymerase chain reaction technique. It also confirmed the dominance of electroactive species in the bio-anodic sludge of MFC-B over the bio-anodic sludge of MFC-A. Cyclic voltammogram also asserted better electrochemical activity of the bio-cathode in the treatment of chlorinated phenol toxicants in MFC-B system. The study shows that MFC can be a viable option in treatment of recalcitrant chemical compounds like TCP with the generation of energy in the form of electrical power.

Antioxidant and antibacterial activities of exopolysaccharides produced by lactic acid bacteria isolated from yogurt

The objectives of this study were to optimize the conditions for cell growth and exopolysaccharides (EPS) production by using pure and mixed microbial cultures of Streptococcus thermophilus and Lactobacillus bulgaricus , and to evaluate the antioxidant and antibacterial activities of EPS in vitro . The mixed cultures of two strains showed a higher cell growth whereas the higher EPS production was detected in pure culture with S. thermophilus . The optimal medium were determined as follows (g/l): sucrose 50, yeast extract 10, KH 2 PO 4 3 , MgSO 4 .7H 2 O 0.05 and pH initial 6.5 at 30°C. Under the optimized conditions, the values of dry cell weight (DCW) and EPS were 5.2± 0.8 g/l and 56.8 ± 0.62 mg/ml, respectively. The EPS demonstrated a positive antioxidant potential on DDPH radical scavenging. The agar diffusion assay showed that purified EPS exhibited antibacterial activities against tested pathogens such as Escherichia coli ATCC 250922 and Staphyloccocus aureus ATCC 250923 at (62-1000) μg/mL. In conclusion, EPS have an antioxidant activity and could have applications in the food industry.

Antioxidant and antibacterial activities of exopolysaccharides produced by lactic acid bacteria isolated from yogurt

The objectives of this study were to optimize the conditions for cell growth and exopolysaccharides (EPS) production by using pure and mixed microbial cultures of Streptococcus thermophilus and Lactobacillus bulgaricus, and to evaluate the antioxidant and antibacterial activities of EPS in vitro. The mixed cultures of two strains showed a higher cell growth whereas the higher EPS production was detected in pure culture with S. thermophilus. The optimal medium were determined as follows (g/l): sucrose 50, yeast extract 10, KH2PO4 3 , MgSO4.7H2O 0.05 and pH initial 6.5 at 30°C. Under the optimized conditions, the values of dry cell weight (DCW) and EPS were 5.2± 0.8 g/l and 56.8 ± 0.62 mg/ml, respectively. The EPS demonstrated a positive antioxidant potential on DDPH radical scavenging. The agar diffusion assay showed that purified EPS exhibited antibacterial activities against tested pathogens such as Escherichia coli ATCC 250922 and Staphyloccocus aureus ATCC 250923 at (62-1000) μg/mL. In conclusion, EPS have an antioxidant activity and could have applications in the food industry.

Assessment of Protein-Rich Cheese Whey Waste Stream as a Nutrients Source for Low-Cost Mixed Microbial PHA Production

The critical step in the mixed microbial cultures (MMC) polyhydroxyalkanoates (PHA) production process is the selection of an MMC enriched in an efficient PHA-accumulating organism, usually requiring growth-nutrients supplementation. This study aimed at assessing cheese whey (CW) proteins as a source of nitrogen for PHA-producing MMC, thus eliminating or reducing the need for nutrients supplementation. The selection reactor, operated with fermented CW, under a feast–famine regime, was initially supplemented with ammonia–nitrogen in a C/N ratio of 100/15 (Cmol/Nmmol), which was gradually reduced until eliminated, in order to select a culture capable of using CW proteins nitrogen. Decreasing nitrogen supplementation from a C/N ratio of 100/10 to 100/7.5 lead to significant microbial community changes, and reduced the MMC PHA-storing capacity, storage yield, and PHA productivity, decreasing by 30%, and over 45%, respectively. The PHA-storing capacity further deteriorated as nitrogen supplementation was reduced, despite increased protein-uptake. Results show that a culture enriched in PHA-accumulators capable of using proteins as sole nitrogen source could not be attained. In conclusion, this work reports for the first time that an easily bioavailable nitrogen source is required for efficiently selecting PHA-accumulating cultures. Based on the results obtained from this work, a pilot scale plant (two reactors of 100 L) fed with cheese whey for production of PHA is currently being successfully operated under the scope of the YPACK EU project, in which the selection reactor is supplemented with nitrogen (ammonia) from a total C/N ratio of 100/10.

Bioconversion of Giant Cane for Integrated Production of Biohydrogen, Carboxylic Acids, and Polyhydroxyalkanoates (PHAs) in a Multistage Biorefinery Approach

A highly productive Arundo donax L. clone (Clone AD-20) was produced at full field to give 54.6 Mg total solids biomass Ha–1. Biomass was chemically and enzymatically pretreated, recovering 13.9 Mg Ha–1 of glucose and 3.6 Mg Ha–1 of xylose, i.e., 3.5–4.5 more than yield typically obtained from corn stover or switchgrass. The subsequent fermentation of the liberated sugars to organic acids (OA) by dark fermentation generated yields of 3850 Nm3 Ha–1 of biohydrogen and 14.2 Mg Ha–1 of OAs. OAs were then used as a feed to produce polyhydroxyalkanoates (PHA), with 3-hydroxybutyrate the major monomer present (PHB > 95% PHA), from a biological process using mixed microbial culture producing 5.04 Mg Ha–1 of PHA. An initial economic analysis indicated that this multistage biorefinery approach would result in a net revenue of 10,415 € Ha–1, which is approximately 9-fold greater than that obtained by a traditional biorefinery producing bioethanol.

Increasing cell concentration does not affect specific ferrous iron oxidation rate in a continuously stirred tank bioreactor

Microbial oxidation of ferrous to ferric iron allows efficient oxidative processing of sulfide minerals under ambient conditions. This study determined the effect of cell concentration of a mixed mesophilic microbial culture on iron oxidation rate, and evaluated if there was a cell concentration threshold that dictates a maximal volumetric iron oxidation rate. A bioreactor with feedback-loading of ferrous media was operated at 30 °C to maintain a redox potential of +480 mV vs. Ag/AgCl at pH of 1.3. A positive and linear correlation (R2 = 0.955) between the cell concentration (6.8 × 107–7.1 × 109 cells mL−1) and volumetric biological iron oxidation (up to 6.9 g L−1 h−1) was observed. The specific iron oxidation was not affected by cell concentration, and no biocatalytic threshold was observed. This indicated that a high cell concentration can be used to achieve a high volumetric iron oxidation rate, enabling the use of a compact reactor size.

Comparative study of polyhydroxyalkanoates production from acidified and anaerobically treated brewery wastewater using enriched mixed microbial culture

The production of polyhydroxyalkanoates (PHA) from wastewaters using microbial mixed cultures (MMC) has been attracting increased interest because of PHA's biodegradability characteristics. Production of PHA by an MMC enriched with PHA-accumulating bacteria was compared using anaerobically treated and acidified brewery wastewaters under various feeding strategies, namely pulse and batch feed addition. To obtain an enriched MMC, a sequencing batch reactor was inoculated with activated sludge fed with acetate and subjected to aerobic dynamic feeding. The enriched MMC was able to accumulate PHA up to 72.6% of cell dry weight (CDW) with pulse addition of acetate controlled by the dissolved oxygen (DO) concentration in the reactor. In a batch accumulation experiment with acetate, the PHA content achieved (28.5% CDW) was less than that of the pulse feeding strategy with the same amount of acetate (~2000 mg C/L). Using anaerobically treated and acidified brewery wastewater fed in pulses, the maximum PHA accumulated by the enriched MMC was similar for both wastewaters (45% CDW), in spite of the higher volatile fatty acid concentration in acidified brewery wastewater. The pulse feed addition controlled by the DO concentration was difficult to implement for wastewater as compared to acetate because the difference in DO concentration between substrate availability and depletion was low. For the batch addition of acidified wastewater, a slightly lower PHA content (39% CDW) was obtained. These results show that both brewery wastewaters can be utilized for PHA production with a similar maximum PHA storage capacity.

Response of Secondary Metabolism of Hypogean Actinobacterial Genera to Chemical and Biological Stimuli.

Microorganisms within microbial communities respond to environmental challenges by producing biologically active secondary metabolites, yet the majority of these small molecules remain unidentified. We have previously demonstrated that secondary metabolite biosynthesis in actinomycetes can be activated by model environmental chemical and biological stimuli, and metabolites can be identified by comparative metabolomics analyses under different stimulus conditions. Here, we surveyed the secondary metabolite productivity of a group of 20 phylogenetically diverse actinobacteria isolated from hypogean (cave) environments by applying a battery of stimuli consisting of exposure to antibiotics, metals, and mixed microbial culture. Comparative metabolomics was used to reveal secondary metabolite responses from stimuli. These analyses revealed substantial changes in global metabolomic dynamics, with over 30% of metabolomic features increasing more than 10-fold under at least one stimulus condition. Selected features were isolated and identified via nuclear magnetic resonance (NMR), revealing several known secondary metabolite families, including the tetarimycins, aloesaponarins, hypogeamicins, actinomycins, and propeptins. One prioritized metabolite was identified to be a previously unreported aminopolyol polyketide, funisamine, produced by a cave isolate of Streptosporangium when exposed to mixed culture. The production of funisamine was most significantly increased in mixed culture with Bacillus species. The biosynthetic gene cluster responsible for the production of funisamine was identified via genomic sequencing of the producing strain, Streptosporangium sp. strain KDCAGE35, which facilitated a deduction of its biosynthesis. Together, these data demonstrate that comparative metabolomics can reveal the stimulus-induced production of natural products from diverse microbial phylogenies.IMPORTANCE Microbial secondary metabolites are an important source of biologically active and therapeutically relevant small molecules. However, much of this active molecular diversity is challenging to access due to low production levels or difficulty in discerning secondary metabolites within complex microbial extracts prior to isolation. Here, we demonstrate that ecological stimuli increase secondary metabolite production in phylogenetically diverse actinobacteria isolated from understudied hypogean environments. Additionally, we show that comparative metabolomics linking stimuli to metabolite response data can effectively reveal secondary metabolites within complex biological extracts. This approach highlighted secondary metabolites in almost all observed natural product classes, including low-abundance analogs of biologically relevant metabolites, as well as a new linear aminopolyol polyketide, funisamine. This study demonstrates the generality of activating stimuli to potentiate secondary metabolite production across diverse actinobacterial genera.

Galacturonate Metabolism in Anaerobic Chemostat Enrichment Cultures: Combined Fermentation and Acetogenesis by the Dominant sp. nov. "Candidatus Galacturonibacter soehngenii".

Agricultural residues such as sugar beet pulp and citrus peel are rich in pectin, which contains galacturonic acid as a main monomer. Pectin-rich residues are underexploited as feedstocks for production of bulk chemicals or biofuels. The anaerobic, fermentative conversion of d-galacturonate in anaerobic chemostat enrichment cultures provides valuable information toward valorization of these pectin-rich feedstocks. Replicate anaerobic chemostat enrichments, with d-galacturonate as the sole limiting carbon source and inoculum from cow rumen content and rotting orange peels, yielded stable microbial communities, which were dominated by a novel Lachnospiraceae species, for which the name "Candidatus Galacturonibacter soehngenii" was proposed. Acetate was the dominant catabolic product, with formate and H2 as coproducts. The observed molar ratio of acetate and the combined amounts of H2 and formate deviated significantly from 1, which suggested that some of the hydrogen and CO2 formed during d-galacturonate fermentation was converted into acetate via the Wood-Ljungdahl acetogenesis pathway. Indeed, metagenomic analysis of the enrichment cultures indicated that the genome of "Candidatus G. soehngenii" encoded enzymes of the adapted Entner-Doudoroff pathway for d-galacturonate metabolism as well as enzymes of the Wood-Ljungdahl pathway. The simultaneous operation of these pathways may provide a selective advantage under d-galacturonate-limited conditions by enabling a higher specific ATP production rate and lower residual d-galacturonate concentration than would be possible with a strictly fermentative metabolism of this carbon and energy source.IMPORTANCE This study on d-galacturonate metabolism by open, mixed-culture enrichments under anaerobic, d-galacturonate-limited chemostat conditions shows a stable and efficient fermentation of d-galacturonate into acetate as the dominant organic fermentation product. This fermentation stoichiometry and population analyses provide a valuable baseline for interpretation of the conversion of pectin-rich agricultural feedstocks by mixed microbial cultures. Moreover, the results of this study provide a reference for studies on the microbial metabolism of d-galacturonate under different cultivation regimes.

Evaluation of heavy petroleum degradation using bacterial-fungal mixed cultures

The use of potent microbial mixed cultures is a promising method for the bioremediation of recalcitrant compounds. In this study, eight molds, three yeasts, and four bacterial isolates were screened from an aged oil-polluted area. An oil degradation assay with various combinations including Bacterial Mixed Culture (BMC), Fungal Mixed Culture (FMC), Fungal-Bacterial Mixed Culture (TMC), and Sequential Fungal-Bacterial Mixed Culture (SMC) was investigated. The results indicated that the SMC culture had the highest yield of degradation (65.96%) in comparison with the degradation yields of TMC, FMC and BMC, which were 59.04%, 56.64%, and 47.56%, respectively. The degradation of saturates, aromatics, resins, and asphaltenes in the crude oil found using the Iatroscan system were, as follows: 64.21%, and 67.63% for aromatics, 72.90%, and 73.59% for saturates, and 53.88% and 58.25% for resins with respect to the TMC and SMC cultures as the superior mixed cultures. The growth rates of yeasts, molds, and bacteria in the TMC and SMC cultures were compared for further evaluation of the role of each microorganism in the degradation. Our findings support the use of mixed cultures in the bioremediation of recalcitrant petroleum pollution.

Two-step biohydrometallurgical technology of copper-zinc concentrate processing as an opportunity to reduce negative impacts on the environment

Polymetallic concentrates obtained during ore beneficiation pose a significant problem for the mining and metallurgy industry due to an increase in load on subsequent comminution steps and a high loss of metals in slag during smelting. Storage of such slag can lead to pollution of groundwater due to weathering. Biohydrometallurgy is an option for the processing of sulfidic raw materials that has a low impact on the environment. Processing of sulfidic concentrates of copper-zinc ore via bioleaching techniques was studied in this paper. Three mixed microbial cultures of acidophilic microorganisms were enriched from industrial mining sites: two autotrophic mesophilic cultures containing Acidithiobacillus ferroxidans and Leptospirillum spp. (grown at 30 and 35 °C), and a mixotrophic moderate thermophilic culture containing Sulfobacillus thermotolerans, Leptospirillum ferriphilum, as well as the archaea Ferroplasma acidiphilum and Acidiplasma spp. (grown at 40 °C). The autotrophic microbial culture growing at 30 °C was used to generate an iron-containing biosolution for ferric leaching of a copper-zinc concentrate. Zinc and iron extracted into solution faster than copper during high-temperature (80 °C) ferric leaching of the concentrate due to galvanic interactions between minerals, redox conditions of the medium, and differences between mineral oxidation mechanisms. Weight loss of the leach residue was 34.0%, with relative copper content increased by 1.0%, zinc content decreased by 6.18%, and iron content decreased by 15.1%. Biooxidation of ferrous iron in the pregnant leach solution by three microbial cultures was also studied. The most effective culture was moderate thermophilic. The results of studies on the bioregeneration of leaching solutions are relevant to the development of a two-step biohydrometallurgical technology for processing of copper-zinc concentrate with a closed cycle of technological flows. The ferrous iron biooxidation rate by the moderate thermophilic culture reached 20 g L−1 day−1. The leach residue obtained can be considered a high-grade copper concentrate able to be processed via smelting. This bioleaching process would make it possible to reduce pollution of groundwater by some toxic metals stored in slags. An environmentally friendly technology flow sheet for copper-zinc sulfidic ore processing using two-step bioleaching treatment was proposed.

Impact of Organic Acids Supplementation to Hardwood Spent Sulfite Liquor as Substrate for the Selection of Polyhydroxyalkanoates-Producing Organisms

The effectiveness of polyhydroxyalkanoates (PHAs) production process from a waste stream is determined by the selection of a suitable mixed microbial culture (MMC). In this work, a feedstock from the paper industry, hardwood spent sulfite liquor (HSSL), supplemented with short-chain organic acids (SCOAs) to simulate a fermented effluent, was used as substrate to enrich a MMC in PHA-storing microorganisms. A stable culture was quickly established, and during the accumulation step the selected MMC reached a maximum PHA content of 34.6% (3HB:3HV-76:24). The bacterial community was analyzed through FISH analysis. Bacteria belonging to the four main classes were identified: Betaproteobacteria (44.7 ± 2.7%), Alphaproteobacteria (13.6 ± 1.3%) and Gammaproteobacteria (2.40 ± 1.1%) and Bacteroidetes (9.20 ± 3.8%). Inside the Betaproteobacteria class, Acidovorax (71%) was the dominant genus.

Dark fermentation metabolic models to study strategies for hydrogen consumers inhibition

A Flux Balance Analysis (FBA) metabolic model of dark fermentation was developed for anaerobic mixed cultures. In particular, the model was applied to evaluate the effect of a specific inoculum pre-treatment strategy, addition of waste frying oil (WFO) on H2-producing and H2-consuming metabolic pathways. Productions of volatile fatty acid (VFAs), CO2, H2 and CH4 measured through triplicate batch experiments, were used as constraints for the FBA model, to compute fluxes trough different metabolic pathways. FBA model could estimate the effect of pre-treatment with WFO on major microbial populations present in the mixed community (H2 producing bacteria, homoacetogen and methanogens). Results revealed that low concentrations of WFO did not completely inhibited hydrogenotrophic methanogens. FBA showed that acetoclastic methanogens were more sensitive to WFO, in comparison to hydrogenotrophic methanogens. The proposed model can be used to study H2 production by any other mixed microbial culture with similar substrates.

Preparation and Characterization of Electrospun Food Biopackaging Films of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Derived From Fruit Pulp Biowaste

In the present study, circular economy based and potentially low-cost poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was produced by mixed microbial cultures derived from fruit pulp, an industrial by-product of the juice industry. Three different chemical routes, namely non-extraction, extraction with sodium hypochlorite (NaClO), and extraction with chloroform, in combination with filtering and centrifugation, were explored to purify the biopolymer and find the most optimal solution for its processing via electrospinning. The resultant ultrathin fiber mats of the different extracted PHBV materials were thermally post-processed at different temperatures in order to obtain continuous films adequate for food packaging applications. The resultant films were characterized in terms of morphology, crystallinity as well as thermal, mechanical, and barrier properties. The results showed that extraction with both chloroform and NaClO with a post-treatment of filtering and centrifugation of the PHBV-containing biomass were necessary refining steps to allow its processing by electrospinning. In particular, the PHBV extracted with chloroform presented the highest degree of purity, resulting in more transparent films with lower wettability and higher flexibility. The here-formulated electrospun films made of biomass derived from biowaste exhibit great potential as interlayers or coatings for food biopackaging applications.

Metabolic modeling of the substrate competition among multiple VFAs for PHA production by mixed microbial cultures

Mixed microbial cultures (MMCs) are an effective method for polyhydroxyalkanoates (PHA) production. There are several models established to describe the metabolism of this process. Substrate competition was commonly found in the uptake of multiple volatile fatty acids (VFAs), thus this behavior should be considered in process modeling. In this study, a metabolic model is developed to describe for the first time the substrate competition among four commonly used VFAs (acetate, propionate, butyrate and valerate) in PHA production by MMCs. An inhibition parameter was introduced to describe the inhibition of butyrate and valerate on the uptake of acetate and propionate. The modeled results showed good agreement with experimental data within 95% confidence interval. This model enhanced the understanding of the metabolism of substrate uptake in PHA production, providing a successful approach to predict PHA composition and optimize the process efficiency when four competing VFAs are supplied.