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Water and glucose gradients in the substrate measured with NMR imaging during solid‐state fermentation with Aspergillus oryzae
Author(s) -
Nagel FrankJan,
Van As Henk,
Tramper Johannes,
Rinzema Arjen
Publication year - 2002
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.10332
Subject(s) - aspergillus oryzae , fermentation , moisture , substrate (aquarium) , chemistry , matrix (chemical analysis) , diffusion , solid state fermentation , food science , evaporation , water content , microorganism , water activity , biophysics , chromatography , biology , ecology , bacteria , geology , thermodynamics , organic chemistry , physics , genetics , geotechnical engineering
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. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 79: 653–663, 2002.