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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]

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 ( Mn P) (1690.3 ± 87.6), lignin peroxidase ( Li P) (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. [ABSTRACT FROM AUTHOR]

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]