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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. [ABSTRACT FROM AUTHOR]

Summary 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. [ABSTRACT FROM AUTHOR]

Abstract: In view of ever growing demand of citric acid, there is an urgent need to look for inexpensive and novel substrates for feasible production of citric acid. In this context, the present study was carried out to evaluate the potential of different agro-industrial wastes for hyper production of citric acid through solid-state and submerged fermentation by Aspergillus niger NRRL 567 and NRRL 2001. It was found that among all the solid substrates utilized, apple pomace with 66.0±1.9g/kg of dry substrate proved to be an excellent substrate for citric acid production by A. niger NRRL 567 at 72h of incubation. A. niger NRRL 2001 resulted in slightly lower citric acid concentration of 61.0±1.9g/kg of dry substrate at the same incubation time. APS-1 (apple pomace ultrafiltration sludge-1) gave highest citric acid production rate of 9.0±0.3g/l and 8.9±0.3g/l of substrate by A. niger NRRL 567 and NRRL 2001 by submerged fermentation, respectively. Further study with apple pomace and apple pomace ultrafiltration sludge-1 by A. niger NRRL 567 was carried out. Addition of 3% (v/w) ethanol and 4% (v/w) methanol to apple pomace gave significantly higher citric acid values of 127.9±4.3g/kg and 115.8±3.8g/kg of dry substrate by A. niger NRRL 567 by solid-state fermentation. Higher citric acid values of 18.2±0.4g/l and 13.9±0.4g/l of apple pomace ultrafiltration sludge-1 were attained after addition of 3% (v/v) ethanol and 4% (v/v) methanol, respectively by A. niger NRRL 567. Apple pomace solid waste and apple pomace ultrafiltration sludge-1 thus proved to be an excellent source for citric acid production, of the different substrates chosen. [Copyright &y& Elsevier]

Abstract: Solid-state citric acid fermentation was conducted in a 12-L rotating drum type bioreactor. The effect of inducers, ethanol and methanol were studied on citric acid bioproduction by Aspergillus niger NRRL 567 cultivated on apple pomace as a solid-substrate. Optimum conditions achieved for higher citric acid bioproduction (220.6±13.9g/kg dry solids, DS) were 3% (v/v) methanol, intermittent agitation of 1h after every 12h at 2rpm and 1vvm of aeration rate and 120h incubation time. The response surface optimization proved effective for higher citric acid extraction from fermented solid-substrate. Higher citric acid extraction of 294.19g/kg DS was achieved at optimum conditions: extraction time of 20min, agitation rate of 200rpm and extractant volume of 15ml by response surface methodology. [Copyright &y& Elsevier]