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Polyol accumulation by Aspergillus oryzae at low water activity in solid-state fermentation
George J G Ruijter1,2, Jaap Visser2, Arjen Rinzema3,2
1Wageningen University, Laboratory of Microbiology, Dreijenlaan 2, 6703HA Wageningen, The Netherlands.
Microbiology (Reading, England)
|April 10, 2004
Summary
Aspergillus oryzae accumulates unusual polyols like glycerol and erythritol under osmotic stress in solid-state fermentation. These polyols, along with mannitol, are regulated by specific dehydrogenases, suggesting adaptation to low water activity.
Area of Science:
- Microbiology
- Biochemistry
- Food Science
Background:
- Solid-state fermentation (SSF) involves low water activity (a(w)), creating osmotic stress for microorganisms.
- Aspergillus oryzae is a fungus used in food fermentation, but its response to osmotic stress in SSF is not fully understood.
Purpose of the Study:
- To investigate polyol accumulation and metabolism in Aspergillus oryzae during solid-state culture.
- To identify the enzymes involved in polyol biosynthesis under osmotic stress.
Main Methods:
- Culturing Aspergillus oryzae on whole wheat grains and wheat dough to model SSF.
- Measuring polyol concentrations and polyol dehydrogenase activities in fungal mycelia.
- Analyzing the correlation between enzyme activity and polyol accumulation.
Main Results:
- A. oryzae accumulated high concentrations of glycerol, erythritol, and arabitol, in addition to mannitol, at low a(w) (0.96-0.97).
- At least four distinct polyol dehydrogenases were identified, with high activity towards glycerol, erythritol, D-arabitol, and mannitol.
- NADP(+)-dependent glycerol and erythritol dehydrogenase activities strongly correlated with the accumulation of their respective polyols.
Conclusions:
- The accumulation of a mixture of polyols is characteristic of A. oryzae in SSF under osmotic stress.
- NADP(+)-dependent glycerol and erythritol dehydrogenases are likely involved in the biosynthesis of these polyols and are induced by osmotic stress.
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