Biotechnological potential of industrial wastes for economical citric acid bioproduction by Aspergillus niger through submerged fermentation

Submerged citric acid (CA) bioproduction was carried out by Aspergillus niger NRRL‐567 using various industrial wastes, such as brewery spent liquid (BSL), lactoserum and starch industry water sludge. CA bioproduction was carried out by varying the temperature (25–35 °C), pH (3–5), addition of inducers, incubation time and supplementation with different proportions of apple pomace ultrafiltration sludge (APS). The results indicated that under the best conditions with 3% (v/v) methanol, the optimal concentration of 11.34 g L^?1 CA was recorded using BSL at pH 3.5 and temperature 30 °C after 120‐h incubation period. Supplementation of methanol resulted in an increase of 56% CA production. Meanwhile, under similar conditions, higher concentration of 18.34 g L^?1 CA was reported with the supplementation of BSL with 40% (v/v) APS having suspended solids concentration of 30 g L^?1. The present study demonstrated the potential of BSL supplemented with APS as an alternative cheap substrate for CA fermentation.     

Periodically Fully Developed Heat and Fluid Flow Characteristics in a Furrowed Wavy Channel

Periodically fully developed two-dimensional (2D) flow in a furrowed wavy channel is investigated numerically at various Reynolds numbers (100–2123). For the laminar and transitional flow regime, the study is done for six geometrically different channels; corresponding to various nondimensional amplitude (0.05, 0.075, and 0.1) and wavelength (0.5 and 1). Critical Reynolds number—for the onset of periodic flow—decreases with increasing amplitude and wavelength. A flow regime map—demarcating steady and unsteady flow regime—is proposed. It is shown that the size of the vortex in streamlines and waviness in isotherms increase with increasing Reynolds number, amplitude and wavelength. The performance of wavy as compared to straight channel is studied with the help of ratio of Nusselt number, friction factor and area-goodness factor, and thermal-performance factor. With increasing Reynolds number, all these parameters remain almost constant in the steady regime and increase almost linearly in the unsteady regime. For the largest Reynolds number (close to 2000) studied here, the increase in the Nusselt number ratio—within the periodic flow regime—is 11.21% and 133% for the amplitude equal to 0.075 and 0.1, respectively, at a wavelength of 0.5; at a wavelength of 1.0, the increase is 101%, 134%, and 181% for the amplitude of 0.05, 0.075, and 0.1, respectively.     

Apple pomace ultrafiltration sludge – A novel substrate for fungal bioproduction of citric acid: Optimisation studies

Ever-growing demand for citric acid (CA) and urgent need for alternative sources has served as a driving force for workers to search for novel and economical substrates. Submerged fermentation was conducted using apple (Malus domestica) pomace ultrafiltration sludge as an inexpensive substrate for CA bioproduction, using Aspergillus niger NRRL567. The crucial parameters, such as total suspended solids and inducer concentration, were optimised by response surface methodology for higher CA production. The optimal CA concentrations of 44.9 g/100 g and 37.9 g/100 g dry substrate were obtained with 25 g/l of initial total solids and 3% (v/v) methanol and 25 g/l of total solids and 3% (v/v) ethanol concentration, respectively, after the 144 h of fermentation. Results indicated that total solids concentration, and methanol as an inducer, were effective with respect to higher CA yield and also indicated the possibility of using apple pomace sludge as a potential substrate for economical production of CA.     

Influence of aeration and agitation modes on solid‐state fermentation of apple pomace waste by Phanerochaete chrysosporium to produce ligninolytic enzymes and co‐extract polyphenols

The effect of different types of agitation (i) continuous agitation (C); (ii) continuous, discontinuous, continuous agitation (C/D/C); (iii) discontinuous, continuous, discontinuous agitation (D/C/D) and aeration (0.87, 1.25, 1.66 vvm) on ligninolytic enzyme production and polyphenolic compounds extraction by solid‐state cultures of Phanerochaete chrysosporium BKM‐F‐1767 was investigated. Higher production of manganese peroxidase (MnP) (1690.3 ± 87.6), lignin peroxidase (LiP) (387.9 ± 14.3) and laccase (898.9 ± 53.3 U gds^?1) and liberation of total polyphenolics (ranging from 12.22 ± 1.1 to 30.12 ± 0.88 mg gallic acid equivalents per gram DW) was obtained after 195, 147, 219 and 204 h of fermentation, respectively, using 1.66 vvm as airflow and (C/D/C) agitation mode. Maximal enzyme production and total polyphenolic content were influenced by aeration, and higher values were obtained using 1.66 vvm as airflow rate, followed by 1.25 and 0.83 vvm, respectively. They were also influenced by agitation, and maximal values were obtained using C/D/C, followed by D/C/D and continuous agitation, respectively. The agitation modes influenced the production of ligninolytic enzymes and simultaneous extraction of polyphenols.     

MspA Porin-Gold Nanoparticle Assemblies: Enhanced Binding through a Controlled Cysteine Mutation

In this study, the interactions of two gold nanoparticles of different sizes (average diameters of 3.7 +/- 2.6 and 17 +/- 3 nm) with octameric mycobacterial porin A from Mycobacterium smegmatis (MspA) and a mutant of MspA featuring a cysteine mutation in position 126 (Q126C) are investigated. From the observation of enhanced photoluminescence quenching, it is inferred that the presence of eight cysteines in the MspA Q126C mutant significantly enhances the binding of selected small gold nanoparticles within the inner pore of MspA. The large gold nanoparticle/porin complex shows photoluminescence enhancement, which is expected since the larger nanoparticles cannot dock within the homopore of MspA due to size exclusion. In addition to the fluorescence experiments, observation of energy transfer from the small gold nanoparticles to the MspA shows the close proximity of the small gold nanoparticles with the porin. Interestingly, the energy transfer of the large nanoparticle/MspA complex is completely missing. From high-performance liquid chromatography data, the estimated binding constants for small Au@MspA, large Au@MspA, small Au@MspAcys, and large Au@MspAcys are 1.3 x 10 (9), 2.22 x 10 (10), > 10 (12) (irreversible), and 1.7 x 10 (10), respectively.     

Rheological Studies During Submerged Citric Acid Fermentation by Aspergillus niger in Stirred Fermentor Using Apple Pomace Ultrafiltration Sludge

Rheological profile studies for apple pomace ultrafiltration sludge (APS) broth with filamentous fungus, Aspergillus niger NRRL-567 during citric acid (CA) fermentation are reported for the biomass developed in a 7.5 l bench scale fermentor. CA bioproduction of 23.67?±?1.0 g/l APS and 40.34?±?1.98 g/l APS was obtained in control (120 h) and in treatment with inducer, MeOH 3% (v/v), respectively, after 132 h of fermentation by A. niger NRRL 567. The rheological properties of the fermentation broth including pellets were analyzed. The control demonstrated non-Newtonian pseudoplastic behaviour due to more filamentous growth. However, in treatment supplemented with inducer (methanol), pellet form was observed during fermentation with less viscous non-Newtonian broths. The power law model was followed with good confidence of fit (77.8–88.9%) throughout the fermentation in treatment with MeOH as an inducer. However, power law was followed with moderate fit of confidence (65.3–75.9%) at the beginning of fermentation until 48 h and later followed a good confidence of fit (75.9–88.2%) until 144 h of fermentation in control. Important rheological changes occurred in the broth during maximal CA production phase along with increase in biomass in the pelleted mycelium form.     

Co‐culture strategies for increased biohydrogen production

Biological hydrogen production from organic wastes is a less expensive, less energy‐demanding, and environmental‐friendly process. Pure monoculture delivers low H₂ content and low yield; these limitations are overcome by a defined co‐culture system, which outperforms mixed cultures with increased H₂ yield. The strategies used in co‐culture systems for increasing H₂ production have been discussed in this review. The strategies include hydrolysis of a variety of complex substrates, such as cellulose, molasses, crude glycerol, and algal biomass into simple fermentable sugars for increased H₂ yield by eliminating the use of exogenous enzymes. The strategies can bring geographically distant isolated microorganisms from different sources to coexist for simultaneous utilization of substrate and end metabolites into H₂ production of 99.99% purity without the expenses of reducing agents. In the case of maximum hydrogen production using co‐culture strategies, Clostridium, Enterobacter, and photo‐fermenting bacteria in a consolidated bioprocess system will result in increased H₂ yield. A co‐culture system is more feasible to achieve theoretical H₂ yield with high conversion efficiency of organic wastes, enhance the economic viability of H₂ production, provide better effluent treatment quality, and concurrently address the limitations of H₂ production. Copyright © 2015 John Wiley & Sons, Ltd.     

Quest for sustainable bio‐production and recovery of butanol as a promising solution to fossil fuel

Biobutanol has conventionally been generated by fermentation of carbohydrates derived from biomass (starch or sugar‐based feedstock, such as corn) using Clostridia strains (mainly C. beijerinckii and C. acetobutylicum) under anaerobic conditions in batch mode. Under these premises, it has been tough for the acetone–butanol–ethanol fermentation to compete with petro‐butanol production from an energy efficiency and material consumption standpoint. Challenges for butanol production from biomass comprised high cost of feedstock, scarcity of hyper‐butanol producing bacteria and low butanol yield, volumetric productivity and titre, leading to high water usage and separation‐purification costs. This article is an up‐to‐date review on several under explored sections, such as optimization of fermenter feed, microbial culture responsible for solvent production (co‐culture techniques and electro‐biochemical process), latest recovery techniques and the studies integrating in situ continuous fermentation processes. Biobutanol refinery way forward should build upon the use of low‐cost lignocellulosic matter and zero cost organic wastes and by‐products from food, agriculture, forestry, fermentation and paper industries as feedstock; optimized fermentation of such diversified feed with appropriate hyper‐butanol producing strains in biofilm reactors and integration of fermentation step with hybrid high butanol‐selective recovery techniques. Copyright © 2015 John Wiley & Sons, Ltd.