ABSTRACT
INTRODUCTION Food is correlated with fungi in two opposite ways. In a positive way, we think of traditional and exotic fermented foods from different parts of the world. The variety of those foods is wide, ranging from tempe and soy sauce in Asia to different types of cheese in Europe and the Middle East (Campbell-Platt, 1994). For the case of these fermented foods, we use the ability of fungi to degrade complex polymeric substrates to smaller compounds that are easily taken up by men. Some fungi can also consecutively convert the degraded compounds into other type of desirable metabolic products that determine the typical composition, taste, odour, consistency and colour of fermented foods. In a negative way, we think of unwanted spoilage or rotting of foods. A negative view on fungi includes exactly the same principles of digestion of complex substrates and production of other products. In both views the benefit of the fungi is served namely, the optimal survival by living in, growing on, and colonising a food matrix. The process of how fungi grow on and colonise a solid food matrix is described as solid-substrate or solid-state fermentation (SSF). A growing interest in SSF has been shown by a significant increase in numbers of publications on this topic in the past 20 years. Sufficient knowledge about the process of how fungi interact with a substrate matrix is absolutely needed to manipulate SSF processes, in order to: (1) improve the desired fermented
(food) products yield and quality, and (2) prevent food spoilage. However, the knowledge of basic phenomena and their influence on metabolic responses in SSF is still relatively limited including such subjects as kinetics of enzyme production, release and transport, and kinetics of substrates conversion. Those processes are determined by transport phenomena of substrates, metabolites and hydrolytic enzymes. Knowledge of these transport phenomena is crucial to a further understanding of the kinetics in SSF. In this chapter, transport phenomena during fungal colonisation on a substrate matrix are described. Firstly, the occurrence of those phenomena and the complex consequences in SSF are explained. Secondly, some examples from published modelling and experimental work using diffusive transport phenomena are shown. Due to the complex features of SSF and based on diffusion as the transport mechanism, many authors have produced mathematical models to study and understand SSF, e.g., to predict biomass growth. Finally, possible transport phenomena other than diffusion are discussed. FUNGAL BIOMASS AND SUBSTRATE LAYERS The “system” of fungal colonisation on or/and in a substrate matrix consists of three entities: fungal biomass, substrate fragments, and water (Figure 1).
