title: Enhanced solid-state citric acid bio-production using apple pomace waste through surface response methodology.
abstract: OBJECTIVE
  To evaluate the potential of apple pomace (AP) supplemented with rice husk for hyper citric acid production through solid-state fermentation by Aspergillus niger NRRL-567. Optimization of two key parameters, such as moisture content and inducer (ethanol and methanol) concentration was carried out by response surface methodology.
  
  
  RESULTS
  In this study, the effect of two crucial process parameters for solid-state citric acid fermentation by A. niger using AP waste supplemented with rice husk were thoroughly investigated in Erlenmeyer flasks through response surface methodology. Moisture and methanol had significant positive effect on citric acid production by A. niger grown on AP (P < 0·05). Higher values of citric acid on AP by A. niger (342·41gkg(-1) and 248·42gkg(-1) dry substrate) were obtained with 75% (v/w) moisture along with two inducers [3% (v/w) methanol and 3% (v/w) ethanol] with fermentation efficiency of 93·90% and 66·42%, respectively depending upon the total carbon utilized after 144h of incubation period. With the same optimized parameters, conventional tray fermentation was conducted. The citric acid concentration of 187·96gkg(-1) dry substrate with 3% (v/w) ethanol and 303·34gkg(-1) dry substrate with 3% (v/w) methanol were achieved representing fermentation efficiency of 50·80% and 82·89% in tray fermentation depending upon carbon utilization after 120h of incubation period.
  
  
  CONCLUSIONS
  Apple pomace proved to be the promising substrate for the hyper production of citric acid through solid-state tray fermentation, which is an economical technique and does not require any sophisticated instrumentation.
  
  
  CONCLUSIONS
  The study established that the utilization of agro-industrial wastes have positive repercussions on the economy and will help to meet the increasing demands of citric acid and moreover will help to alleviate the environmental problems resulting from the disposal of agro-industrial wastes.
authors.affiliation: INRS-ETE, Université du Québec, Québec City, QC, Canada Institut de recherche et de développement en agroenvironnement inc. (IRDA), Québec City, QC, Canada.
authors.forename: G S
authors.initials: GS
authors.lastname: Dhillon
authors.forename: S K
authors.initials: SK
authors.lastname: Brar
authors.forename: M
authors.initials: M
authors.lastname: Verma
authors.forename: R D
authors.initials: RD
authors.lastname: Tyagi
mesh_terms: D001234:Aspergillus niger / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D005525:Food-Processing Industry; D007220:Industrial Waste; D027845:Malus; D000432:Methanol / Q000378:metabolism
chemical_list: D007220:Industrial Waste; D019343:Citric Acid; D000431:Ethanol; D000432:Methanol