Mesophilic Culture Research Articles

An alternative approach to recover lead, silver and gold from black gossan (polymetallic ore). Study of biological oxidation and lead recovery stages

A novel procedure to recover lead, silver and gold from polymetallic sulphide ores, cleaner than the traditional hydrometallurgical route (hot brine leaching), is proposed. This process consists of a biooxidation stage, where sulphides are oxidised by the action of extremophiles, followed by an acid washing and a citrate leaching in which lead is recovered. The final solid obtained, mainly composed of quartz, is rich in silver and gold. This paper is focused on the biooxidation and the lead recovery of the black gossan, a polymetallic sulphide ore with valuable amounts of lead, silver and gold. Biooxidation performed with a mixed mesophilic culture (mainly Acidithiobacillus ferrooxidans) at 20% pulp density is able to dissolve the sulphide matrix, removing the gold refractory behaviour and producing jarosite, beaverite, gypsum and anglesite. A previous sulphuric acid washing of biooxidation residue greatly improves the lead recovery in the citrate stage. In the sulphuric acid washing, jarosite and beaverite are dissolved, being the most important variables the temperature and sulphuric acid concentration. The jarosite dissolution kinetics shows that the rate controlling step is the chemical reaction, with an activation energy of 86.4 kJ/mol. A linear relationship between the jarosite dissolved and lead recovered is found, reinforcing the necessity of a previous H2SO4 washing. The optimal pH range for lead recovery in the citrate solution is 5–9. Pulp densities higher than 5% produces an unstable solution, precipitating a part of the lead. A negative effect of gypsum has been confirmed through several citrate leaching tests performed with pure anglesite. The solid obtained after the studied stages is suitable to recover gold and silver that contains.

Synchrotron Radiation Based Study of the Catalytic Mechanism of Ag+ to Chalcopyrite Bioleaching by Mesophilic and Thermophilic Cultures

The catalytic mechanism of Ag+ for chalcopyrite bioleaching by mesophilic culture (at 30 °C) and thermophilic culture (at 48 °C) was investigated using synchrotron radiation-based X-ray diffraction (SR-XRD) and S K-edge and Fe L-edge X-ray absorption near edge structure (XANES) spectroscopy. Bioleaching experiments showed that copper extraction from chalcopyrite bioleaching by both cultures was promoted significantly by Ag+, with more serious corrosion occurring on the minerals surface. SR-XRD and XANES analyses showed that the intermediates S0, jarosite and secondary minerals (bornite, chalcocite and covellite) formed for all bioleaching experiments. For these secondary minerals, the formation of bornite and covellite was promoted significantly in the presence of Ag+ for both cultures, while Ag+ has almost no effect on the formation of chalcocite. These results provided insight into the catalytic mechanisms of Ag+ to chalcopyrite bioleaching by the mesophilic and thermophilic cultures, which are both probably due to the rapid formation of bornite by Ag+ and the conversion of bornite to covellite.

Bioleaching of arsenopyrite from Janggun mine tailings (South Korea) using an adapted mixed mesophilic culture

This article explores a heap bioleaching technology for the removal of arsenic (As) from mine tailings using the GEOCOAT™ technique. Small-scale columns were operated at fixed temperatures of 20 °C, 30 °C, and 45 °C and at ramped-up temperatures from 25 °C to 45 °C using a mixed mesophilic acidophilic iron and sulfur oxidizing microbial culture, adapted to high As concentration (20 g/L). The packed-bed columns were filled with inert granite pebbles coated with Janggun Mine tailings, irrigated with a 1 g/L ferrous-enriched 0 K medium and aerated with 200 mL/min compressed air. To study the microbial colonization at various stages of the leaching process relative to the initial inoculum, the ramped-up-temperature experiment was conducted in triplicate and the columns were sacrificed after different leaching periods. The fixed-temperature column samples were sampled upon the termination of each experiment, for microbial speciation of the culture attached to the mineral during the leaching of the ore. The As that was released into the solution, the iron oxidation rates, the pH and the redox potential were used to assess the leaching performance of each column. A triangulation of the results between the fixed and the ramped-up temperatures allowed determination of the influence of temperature on As leaching kinetics and microbial distribution. 94–97% As removal was achieved among the various column experiments, 88 days after inoculation. The results showed that increased temperature induced an increased lag in the As leaching phase. Temperature also affected the abundance of acidophilic microorganisms present in the combined bulk volume of the column and on the mine tailings. The mesophilic bacterial species Acidithiobacillus caldus and Leptospirillum ferriphilum were the dominant biooxidation species (> 60%) in both the inoculum applied to the columns and in Col. A operated at a fixed 20 °C. Increased incubation temperature resulted in a decrease in the number of bacterial cells; however, the number of archaeal cells remained similar with a resulting increase in the archaeal dominance at 45 °C. The ramped-up temperature study showed similar results with an increase in both cell numbers and archaeal dominance between day 42 and 84. Overall, this study demonstrated the feasibility of As detoxification from the Janggun Mine tailings using microbial heap leaching.

Influence of X-ray μ-Computed Tomography on the microbial activity of a mixed thermophilic and mesophilic bioleaching culture colonising a mineral surface

X-ray micro-Computed Tomography (X-ray μCT) allows for non-invasive 3D investigations of heap leaching processes. It permits study of mineral liberation, pore network structure in particles or beds, and bioleaching of non-surface mineral grains. A premise for bioleaching studies integrating X-ray μCT is that the metabolic activity of microorganisms is not affected by X-ray energy doses. This study therefore evaluates the compatibility of bioleaching microorganisms with X-ray energy exposure. The X-ray effect on a mixed thermophilic culture suspended in solution was assessed using imaging conditions of 35–150 kV, 200–280 μA and 1–2 hours. Microorganisms were unaffected between 35–90 kV and 200–280 μA while there was some detrimental effect at 120 and 150 kV. The X-ray influence on a mixed mesophilic culture colonising a mineral surface was investigated at 90 kV and 225 μA for a 1 h exposure time. The system was monitored before and after exposure through measurement of: redox potential of the effluent solution, microbial cell concentration, heat output from the colonised surface using isothermal microcalorimetry (IMC), and cell attachment on the ore surface using scanning electron microscopy (SEM). The redox and cell concentration measurements showed insignificant differences between exposed and unexposed samples. Equivalent heat generation and good colonization of the mineral surface was demonstrated, confirming continued microbial activity post exposure, hence recommending its use in support of bioleaching studies.

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.

Investigating the Bioleaching of an Arsenic Mine Tailing Using a Mixed Mesophilic Culture

The aim of this study was to investigate the microbial colonization and arsenic leaching kinetics of South Korean mine tailings containing arsenopyrite at fixed temperatures (20°C, 30°C and 45°C) and at ramped up temperatures (25 to 45°C, with a 2°C daily increase). The experiments were conducted in a packed bed of inert granite pebbles coated with the tailings material and leached with a mesophilic culture dominated by Acidithiobacillus caldus (56%), a lesser percentage of Leptospirillum ferriphilum (29%) and Archaea (15%), using 1 g/L ferrous-enriched 0K medium. The ramped-up temperature experiment was conducted in triplicate and columns were sacrificed after different leach periods to study the evolution of microbial species dominating the colonization. The leaching performance was evaluated using the arsenic released into solution, the iron oxidation rates, the pH and the redox potential. The microbial speciation of the culture attached to the solids during the leach experiment was determined upon completion of each experiment. A steady arsenic solubilisation of between 94 and 97% was observed among the various column experiment after 88 days post inoculation. Microbial speciation performed following the leaching of the mineral indicated a shift of microbial communities in the columns when compared to the initial inoculum.

Investigating the Microbial Metabolic Activity on Mineral Surfaces of Pyrite-Rich Waste Rocks in an Unsaturated Heap-Simulating Column System

Microbial association with and colonisation of mineral surfaces plays a key role in enhancing the extraction of metals from ores during heap bioleaching processes. On the other hand, if uncontrolled, the same association can also lead to the generation of acid rock drainage (ARD) effluents from mine waste. This study aims to measure microbial metabolic activity of a mixed mesophilic culture on the surfaces of pyrite-bearing waste rocks of different grades over time. The waste rocks are milled, size fractionated and coated onto glass beads, to provide a defined surface area. The metabolic activity on the mineral surface is measured with isothermal microcalorimetry (IMC) complemented with scanning electron microscopy (SEM) and analysis of solution chemistry to measure leach agents and metal release into the pregnant leach solution (PLS). The waste rock samples showed a similar degree of leaching when the solution chemistry was analysed, despite having different sulphide content. However, when metabolic activity of the micro-organisms on the mineral surface was measured, greater activity was seen with higher sulphide content. This data informs an ongoing study to establish a flow-through configuration of the biokinetic test for ARD prediction accounting for both leach solution and microbial-mineral interaction as well as differing kinetics of acid-neutralising and generating reactions to enable the refinement of the current batch method.

Insights into Heap Bioleaching at the Agglomerate-Scale

Previous agglomerate-scale heap bioleaching studies have outlined the variations in cell numbers of the liquid and attached phases during colonisation of sterilised ore by a pure culture. In this study, a mixed mesophilic culture was used in agglomerate-scale columns containing non-sterilised low-grade copper ore. Over a six - month period, columns were harvested at various intervals to provide snapshots of the metal distribution and the quantity, location, and ecological variations of mineral-oxidizing microbes within the ore bed. The initial colonisation period in this experiment was dissimilar to previous work, as the indigenous community was retained within the ore-bed throughout acid agglomeration. The overall colonisation phase lasted for approximately 1,000 hours until cell concentrations stabilised. In each column, less than 0.05% of the total cells were found in the leachate, 15-20% in the interstitial phase and the remaining ~80% were attached to the mineral surface. Once cell numbers had stabilised, interstitial cell concentrations were approximately 2,000× greater than those in the leachate. This difference persisted for the duration of the experiment. Copper concentrations in the two liquid phases generally decreased over time, but were on average 50× higher in the interstitial phase. Iron concentrations were more stable, but again were 30× higher in the interstitial phase. This demonstrates that that the difference in cell concentration between the leachate and interstitial phases cannot be explained through diffusion gradients within the system as it is much greater than those observed for the dissolved metals. It also shows that the specific environmental conditions of the interstitial and attached cells are very different to those inferred through analysis of leachates alone.

Biological methanation of CO2 in a novel biofilm plug-flow reactor: A high rate and low parasitic energy process

The performance of a novel biofilm plug flow reactor containing a mixed anaerobic microbial culture was investigated for the conversion of CO2/H2 to CH4. Unlike conventional gas-liquid contactors that depend on agitation, gas diffusion was decoupled from power consumption for mixing by increasing the gas phase inside the reaction space whilst increasing the gas residence time. The mixed mesophilic culture exhibited good biofilm formation and metabolic activity. Within 82days of operation, 99% and 90% CH4 conversion efficiencies were achieved at total gas throughputs of 100 and 150v/v/d, respectively. At a gas input rate of 230v/v/d, methane evolution rates reached 40v/v/d, which are the highest to date achieved by fixed film biomethanation systems. Significant gas transfer related parasitic energy savings can be achieved when using the novel plug flow design as compared to a CSTR. The results and modelling parameters of the study can aid the development of high rate, low parasitic energy biological methanation technologies for biogas upgrading and renewable power conversion and storage systems. The study has also established a reactor system which has the potential of accelerating biotechnology developments and deployment of other novel C1 gas routes to low carbon products.

Impact of furfural on biological hydrogen production kinetics from synthetic lignocellulosic hydrolysate using mesophilic and thermophilic mixed cultures

The impact of furfural on hydrogen production and microbial growth kinetics was assessed using mixed anaerobic cultures at mesophilic and thermophilic conditions. Mesophilic experiments showed a hydrogen yield of 1.6 mol H2/mol initial sugars at 1 g/L furfural which is a 45% enhancement from the control (0 g/L furfural) at a substrate-to-biomass ratio (S°/X°) of 4 gCOD/gVSS. On the other hand, thermophilic experiments showed no enhancement at 1 g/L furfural but rather a 53% decrease in hydrogen yield from its control. Furfural inhibition threshold limit was observed to be greater than 1 g/L for mesophilic experiments and less than 1 g/L for thermophilic experiments. In both cases, 4 g/L was the most recalcitrant furfural concentration, with propionate and lactate the most predominant soluble metabolites in the mesophilic and thermophilic experiments respectively. It was also noted that in the presence of furfural, hydrogen-producers in both mesophilic and thermophilic mixed cultures were inactivated as no hydrogen was produced until furfural was completely degraded irrespective of sugars degradation. This study also presents the kinetics of microbial growth and substrate degradation obtained using the Monod model on MATLAB®, ignoring an inhibition term. IC50 of the mesophilic and thermophilic experiments were 1.03 g/L and 0.5 g/L respectively indicating that the thermophilic hydrogen producers were more strongly affected by furfural than the mesophilic cultures.

Using isothermal microcalorimetry to measure the metabolic activity of the mineral-associated microbial community in bioleaching

Microbial colonisation of mineral ore is critical in efficient mineral solubilisation for metal recovery in heap bioleaching processes. A better understanding of the processes and behaviour by which microorganisms attach to, and colonise, mineral surfaces may help to enhance bioleaching processes. The direct quantification of metabolic activity of mineral associated cells is difficult and has not been demonstrated adequately in ore beds typical of heap leaching. In this investigation, isothermal microcalorimetry (IMC) was used to measure metabolic activity of a mixed mesophilic culture colonising the mineral surface. IMC is non-destructive and measures continuous heat flow from chemical or biological processes. Our results showed an increase of heat output from the colonised surfaces of mineral concentrate in the biotic system with respect to the abiotic system, caused by oxidative reactions facilitated by the mineral-microbial biofilm. This confirmed that the attached microorganisms were metabolically active and facilitated ongoing mineral leaching through regeneration of lixiviants. The progression of mineral colonisation in a mini-column system was monitored using IMC, scanning electron microscopy and conventional wet chemistry measurements.

Comparative study of S, Fe and Cu speciation transformation during chalcopyrite bioleaching by mixed mesophiles and mixed thermophiles

The bioleaching experiments of chalcopyrite were conducted with mixed mesophilic culture (30°C), moderately thermophilic culture (45°C) and extremely thermophilic culture (65°C), respectively. During bioleaching, the S/Fe/Cu speciation was analyzed by synchrotron radiation (SR) based X-ray diffraction (XRD) and S, Fe and Cu K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the chalcopyrite dissolution could be significantly promoted by these mixed cultures, and the promotion effects were enhanced with the increase of bioleaching temperature. For all bioleaching tests, the formation of intermediates S0, jarosite and secondary minerals (chalcocite, bornite and covellite) was detected, in which the formation of bornite, chalcocite and covellite was just related with redox potential. The formation of bornite could accelerate chalcopyrite dissolution, while the decrease of bioleaching microorganisms could reduce chalcopyrite dissolution.

The Effect of Probiotic Lactic Acid Bacteria on the Characteristics of Galotyri Cheese

This study evaluated the effect of probiotic bacteria on the characteristics of the traditional Greek Galotyri cheese. Four Galotyri cheeses were made with the mesophilic starter culture BT002 along with the probiotic strains Lactobacillus acidophilus NCFM, Lactobacillus acidophilus 145, Lactobacillus paracasei subsp. paracasei LbC 81 or Lactobacillus rhamnosus LC 705 and a cheese was also made without the addition of probiotics. The microbiological, physicochemical, aromatic and sensory characteristics of the products were investigating during 30 days of storage at 4oC. The results indicated that probiotics remained above the recommended level for the therapeutic minimum (106 cfu g-1) after 30days. The addition of probiotics did not change the yield, chemical composition and sensory characteristics of Galotyri cheese. A total of 32 aromatic compounds were identified, of these acetaldehyde, diacetyl and acetoin presented in higher levels in cheeses containing probiotic strains. It was concluded that high quality Galotyri cheese with improved health enhancing properties could be produced.

Action of Antimicrobial Copper on Bacteria and Fungi Isolated from Commercial Poultry Hatcheries

ABSTRACT Since 2008, when the US Environmental Protection Agency (EPA) registered copper and its alloys as an antimicrobial agent for contact surfaces, research has demonstrated their antimicrobial activity. The aim of this study was to evaluate the efficacy of antimicrobial copper against bacteria and fungi isolated from commercial poultry hatcheries in order to develop a microbiological control alternative in these environments. Samples were collected from the surfaces of hatcher baskets from two hatcheries. Mesophilic microorganisms and fungi/yeasts were isolated and standardized in concentration of 105 cells/mL. Four copper plates and four stainless steel plates were completely immersed for one minute in bacteria and fungi/yeasts solutions and left to dry for a day at room temperature. Subsequently, samples were collected from the metal plates with the aid of sterile swab and delimiter. These samples were planted onto Plate Count Agar (for mesophilic culture) and Sabouraud Dextrose Agar (for fungi and yeast culture) and incubated at 36°C for 48 hours and at 25°C for 5-7 days, respectively. After incubation, the colonies recovered from the plates were counted according to IN 62 of the Brazilian Ministry of Agriculture. Almost all contamination was eliminated from the surface of copper plates in a single day, while the stainless steel plates proved to be innocuous to the screened microorganisms. Copper, as a contact surface, proved to have important antimicrobial action on bacteria, fungi and yeasts common to hatcheries.

ДОСЛІДЖЕННЯ ПРОЦЕСІВ ФЕРМЕНТАЦІЇ ТА ФІЗИЧНОГО ВИЗРІВАННЯ ВЕРШКІВ У ВЕСНЯНО-ЛІТНІЙ ПЕРІОД РОКУ ПРИ ВИРОБНИЦТВІ МАСЛА З ПРОБІОТИЧНИМИ ВЛАСТИВОСТЯМИ

Метою досліджень було встановити та обґрунтувати оптимальні параметри ферментації та фізичного визрівання вершків при виробництві кисловершкового масла у весняно-літній період року за поєднання класичних для масла змішаних мезофільних культур Flora Danica (FD) – Lactococcus lactis ssp. cremoris, Lactococcus lactis ssp. lactis, Leuconostoc mesenteroides ssp. cremoris, Lactococcus lactis ssp. diacetylactis із термофільною монокультуроюLactobacillus acidophilus пробіотичного штаму La-5 (La-5). Було виготовлено чотири групи кисловершкового масла. У заквашених вершках контролювали активність кислотоутворення за зміною титрованої і активної кислотності та кислотність плазми.
 Встановлено можливість поєднання класичних змішаних мезофільних культур FD з термофільною монокультурою L. acidophilus пробіотичного штаму La-5 за ферментації вершків у технології кисловершкового масла з пробіотичними властивостями. Експериментально встановлено дозу інокуляції і раціональне співвідношення між FD і La-5 у складі заквашувальної композиції безпосереднього внесення – 1 : 1 при вихідній концентрації кожної культури у вершках 1·106 КУО/см3 для виробництва кисловершкового масла з пробіотичними властивостями. Встановлено параметри процесу ферментації та фізичного визрівання вершків за поєднання заквашувальних культур FDта La-5 у весняно-літній період року: температура ферментації (30 ± 1) ºС, тривалість 4 год.; температура фізичного визрівання (5 ± 1) ºС, тривалість 6 год.

AVALIAÇÃO FÍSICO-QUÍMICA, MICROBIOLÓGICA E SENSORIAL DE QUEIJO MINAS FRESCAL DE LEITE DE CABRA DESENVOLVIDO POR ACIDIFICAÇÃO DIRETA E FERMENTAÇÃO LÁTICA

O objetivo deste estudo foi avaliar o efeito da acidificação direta por ácido lático e por adição de cultura starter mesofílica tipo O (Lactococcus lactis subsp. lactis e Lactococcus lactis subsp. cremoris) nas propriedades físico-químicas, microbiológicas e sensoriais de queijo Minas frescal de leite de cabra. Duas formulações de queijo Minas frescal foram elaboradas por acidificação com ácido lático e com cultura mesofílica tipo O e avaliadas quanto a qualidade microbiológica, quantificando S. aureus, psicrotróficos, bactérias láticas, coliformes termotolerantes e quanto a presença de Salmonella sp. Quanto as análises físico-químicas, foram realizadas determinação de gordura, cinzas, umidade, acidez titulável em ácido lático e pH. As modificações físico-químicas no queijo Minas frescal foram avaliadas durante o período de estocagem de 14 dias e analisada a sua aceitabilidade e intenção de compra por meio da avaliação sensorial. Os resultados revelaram que ambas as formulações do queijo Minas frescal apresentavam-se em boas condições higiênico-sanitárias e de consumo. Quanto aos parâmetros físico-químicos, os teores de gordura, cinzas e umidade dos queijos não diferiram significativamente entre si (p < 0,05). O queijo obtido por acidificação direta por ácido lático foi o que apresentou menor contagem de bactérias láticas totais e acidez, maior valor de pH e maior aceitabilidade sensorial e intenção de compra diferindo do queijo obtido por fermentação lática. Os resultados mostram que a forma de acidificação afeta as características do produto e sua aceitação pelos consumidores. A utilização do leite de cabra para produção do queijo Minas frescal apresenta potencial de aplicação na indústria de lácteos, agrega valor, tornando-o um produto alternativo aos consumidores alérgicos ao leite bovino.

Metal biorecovery in acid solutions from a copper smelter slag

Slags from metallurgical processes represent a potential resource of metals but also waste materials that have not been successfully beneficiated to date. For this study, a bulk slag sample from a copper smelter was evaluated under chemical and bacterial leaching conditions to test the solubilization of Cu and Zn in acidic, sulfate-rich solutions. Fayalite, magnetite and glassy silicates as well as Cu-sulfides and sphalerite were the major phases of the slag. The acid demand of the slag was satisfied with a 24h contact time with sulfuric acid. A mixed mesophilic culture capable of oxidizing iron and sulfur and dominated by Acidithiobacillus thiooxidans, A. ferrooxidans, and Leptospirillum ferriphilum was used for bioleaching. The maximum extent of Zn leaching was 14%, contrasted with 83% Cu in experiments with an initial pH of 2.1–2.2, 10% pulp density, 10gL−1S0 addition, 5% inoculum, and 25d contact time. Biological S0 oxidation was an important source of acid in bioleaching experiments. Ferric iron did not enhance the solubilization of Cu and Zn appreciably.

Effect of buffalo milk on the yield and composition of buffalo feta cheese at various processing parameters

Abstract The aim of this study was to analyze the composition of Iranian buffalo milk and study the effect of different parameters such as fat content, acidity of milk, starter culture and temperature on the composition of buffalo feta cheese. The feta cheese yields obtained from buffalo milk were higher in comparison with the yields reported for cow milk. Higher yields were obtained when the fat content of the milk was increased. Rise in the raw milk acidity increased the yield and reduced the fat, protein and lactose loses. Thermophilic and mesophilic starter cultures exhibited better activities at 38 °C and 34 °C, respectively. Pasteurization resulted in significantly (p 0.05). The results of this study revealed that buffalo milk could be regarded as a good source for the production of feta cheese due to elevated amounts of fat, protein and Ca. The results showed that optimum conditions were needed to achieve the higher yields.

Sugarcane Juice Processing: Microbiological Monitoring

This study was undertaken to evaluate a pilot plant designed for sugarcane juice processing. The juice was extracted in an electric mill and acidified with citric acid until the pH of 4.3. Next, it was pasteurized in a plate heat exchanger at 95°C/30 sec, cooled to 10°C before being filled into a plastic bottle and induction sealed. Product filling was performed in an ISO class 5 unidirectional air-flow cabins. Three batches of acidified sugarcane juice were produced. The qualities of the raw material, rinse water of the processing and filling line, packaging and end product were all microbiologically evaluated. Hedonic scale tests were used to evaluate the sensory acceptance of the product. The total mean counts in mesophilic culture of molds and yeasts from the natural, fresh sugarcane juice were (6.26 and 5.20) log CFU/mL, respectively. These mean counts, in both rinse water samples of the processing line and the bottles, were lower than 1 log CFU/mL. The mean counts of molds and yeasts in acidified and pasteurized sugarcane juice were (2.63 and lower than 1) log CFU/mL, respectively. The findings indicated that the procedures that were evaluated met standards for acidified sugarcane juice to be produced then stored under refrigeration.

Long term impact of stressing agents on fermentative hydrogen production: Effect on the hydrogenase flux and population diversity

In this study, the long term effect of different microbial stressing agents on hydrogen (H2) production was examined using repeated batch cultivations. When compared to thermophilic cultures, higher H2 yields were observed in mesophilic cultures receiving repeated glucose addition. Methane production was only observed in control mesophilic cultures receiving repeated 5 glucose additions. Lower hydrogenase evolution specific activity was observed in thermophilic cultures (except alkali-treated cultures) compared to mesophilic cultures. For both mesophilic and thermophilic cultures, the hydrogenase uptake specific activity of the untreated control cultures exhibited higher levels of activity than the pretreated cultures. A flux balance analysis (FBA) showed negligible homoacetogenic flux in mesophilic cultures pretreated with linoleic acid (LA) and loading shock (LS) after successive batch cultivations. The homoacetogenic flux accounted for approximately 98% loss in the H2 yield in untreated mesophilic control cultures. Both homoacetogens (Eubacterium sp.) and aceticlastic methanogens (Methanosaeta sp. and Methanosarcina sp.) were abundant in the control cultures. In comparison, Clostridium sp. were dominant in mesophilic stress treated cultures whereas under thermophilic conditions, the dominant microorganisms were Flavobacterium sp., Bacillus sp., Thermoanaerobacter sp., Bacteroides sp., Lactobacillus sp. and Thioalkalivibrio sp.