Solid-state food fermentations


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Titel Solid-state food fermentations
Looptijd 01 / 2003 - 12 / 2003
Status Afgesloten
Onderzoeknummer OND1295371

Samenvatting (EN)

This project on solid state food fermentations (SSF) integrates process-engineering studies at the fermenter and particle level with studies on physiology, gene expression and morphology. The fungus Aspergillus oryzae grown on wheat or wheat-flour model substrates is used as a model system, amylases and proteases are used as model products. Particularly novel aspects include the modelling of the effects of fungal mycelium on mixing in SSF and vice versa, studies on the effect of aerial mycelia, and transcriptomics- and proteomics-based approaches to detect SSF-specific genes and proteins and identify SSF-specific control elements. Our work on modelling of packed-bed fermentation, modelling of fungal growth and metabolism inside solid particles, and physiology extends previously reported studies to the level of a consolidated approach for design and operation.
In the initial phase of the project discrete element models were developed using a relatively simple drum fermenter. These models for mixing of the solid substrate particles were extended to other fermenter designs. Also heat and moisture distribution as well as the effects of formation of particle agglomerates were included in the model. Breaking up these agglomerates is of critical importance for solid-state fermentation to retain process control. The model predict agglomerates remaining after intermittent mixing, based on independent measurements of mycelium strength. In future research modelling of larger number and variable-sized particles in relation to aggregation due to fungal growth will be addressed.
In non-mixed packed-bed fermenters we demonstrated that mass transfer between particles and gas is not rapid enough to reach equilibrium. Existing process models underestimate the amount of air needed to cool the fermenter. We have adapted our process models to include temperate gradients and moisture loss. We have also extended the models to account for particle shrinkage due to evaporative cooling.
Inter-particle mycelium-bonds present an interesting dilemma: They need to be broken to maintain process control in conventional packed-bed fermenters, but breaking them is deleterious for aerial mycelium. Using wheat-flour model substrate, we have demonstrated that this aerial mycelium can strongly accelerate fungal growth and amylase production. In further experimentation these findings could not directly be implemented to accelerate packed-bed solid-state fermentation. Extension of the models to altered bed configuration (more void space, smaller particles) and industrially relevant, soy based substrates, revealed clear differences, suggesting a more complex relation between respiration and productivity then suggested from the wheat flour model.
Mathematical models were developed for hyphal extension and mycelial mats. To link these models to other aspects of fungal fermentation, such as enzyme production, requires more insight in topology of enzyme production.
We studied regulation of selected SSF specific genes (glucoamylase/protease), revealing an important contribution of nutrient availability and penetrative growth. Mutants with different morphology (hyper-branching) isolated by both classical and recombinant DNA approaches were analysed for gene expression. At least one of these mutants shows altered protein production and altered expression levels for SSF-specific genes. Analysis of cellular physiology under SSF conditions revealed accumulation of a mixture of polyols (glycerol, arabitol, erythritol and mannitol), while in SmF only mannitol was found. In agreement with this several polyol dehydrogenases had increased expression levels in SSF.
New SSF specific proteins have been identified by SDS-PAGE electrophoresis and in gel activity assays. Also a GFP based reporter approach was developed. Based on this and on specific immunodetection with glucoamylase specific antibodies, the study of SSF specific protein secretion and localisation was initiated.
Using transcriptomics-based techniques, we identified at least 5 new genes, specifically induced under SSF conditions. In the final phase of the project these are characterised in more detail

Betrokken organisaties

Betrokken personen

Projectleider Dr. L. Sijtsma

Bovenliggende onderzoeksactiviteit(en)


A34600 Voedingsmiddelen en genotmiddelen
D21300 Biochemie
D22100 Microbiologie

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