title: Water and glucose gradients in the substrate measured with NMR imaging during solid-state fermentation with Aspergillus oryzae.
abstract: Gradients inside substrate particles cannot be prevented in solid-state fermentation. These gradients can have a strong effect on the physiology of the microorganisms but have hitherto received little attention in experimental studies. We report gradients in moisture and glucose content during cultivation of Aspergillus oryzae on membrane-covered wheat-dough slices that were calculated from (1)H-NMR images. We found that moisture gradients in the solid substrate remain small when evaporation is minimized. This is corroborated by predictions of a diffusion model. In contrast, strong glucose gradients developed. Glucose concentrations just below the fungal mat remained low due to high glucose uptake rates, but deeper in the matrix glucose accumulated to very high levels. Integration of the glucose profile gave an average concentration close to the measured average content. On the basis of published data, we expect that the glucose levels in the matrix cause a strong decrease in water activity. The results demonstrate that NMR can play an important role in quantitative analysis of water and glucose gradients at the particle level during solid-state fermentation, which is needed to improve our understanding of the response of fungi to this nonconventional fermentation environment.
authors.affiliation: Wageningen University, Department of Agrotechnology and Food Sciences, Food and Bioprocess Engineering Group, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
authors.forename: Frank-Jan
authors.initials: FJ
authors.lastname: Nagel
authors.forename: Henk
authors.initials: H
authors.lastname: Van As
authors.forename: Johannes
authors.initials: J
authors.lastname: Tramper
authors.forename: Arjen
authors.initials: A
authors.lastname: Rinzema
mesh_terms: D001236:Aspergillus oryzae / Q000737:chemistry / Q000254:growth & development / Q000276:immunology / Q000378:metabolism*; D003198:Computer Simulation; D004058:Diffusion; D005285:Fermentation; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008954:Models, Biological; D008956:Models, Chemical; D011522:Protons; D015203:Reproducibility of Results; D012212:Rheology / Q000379:methods; D012680:Sensitivity and Specificity; D013379:Substrate Specificity; D014908:Triticum / Q000276:immunology / Q000378:metabolism; D014867:Water / Q000737:chemistry / Q000378:metabolism*
chemical_list: D011522:Protons; D014867:Water; D005947:Glucose