ABSTRACT
INTRODUCTION Filamentous fungi colonize food ingredients, penetrating into them, releasing a variety of enzymes, raising metabolites and reaction products and increasing their biomass. In many cases, this sequence of events is considered as spoilage (Pitt and Hocking, 1985) because of off-odours, unwanted discolourations, taste defects, and toxicity. Interestingly, however, mankind experienced that in certain situations, colonizing filamentous fungi (moulds in short) bring about desirable changes in foods, and termed them fermentations (Fukushima, 1985). Considering the chiefly aerobic metabolism of moulds, the usage of the term fermentations - indicating the anaerobic mechanism of energy generation - is incorrect by definition. Nevertheless the term fungal food fermentation is widely accepted in the sense of bioprocesses resulting in improvements of quality. Whereas the origin of fungal food fermentation is the Orient, some specific processes have developed in Europe. Increasing international travel and trade have been the vehicle for the worldwide distribution of some of the derived products. In principle, the birth of fungal food fermentations must have been from "spoilage"; from an ecological point-of-view it may thus be expected that the concept of "spoilage associations" (Dalgaard et al., 2003) also applies to fungal food fermentations. This implies ecological niches consisting of suitable substrate, microbial competition, and favourable envi
ronmental conditions. It therefore seems quite logical to encounter moulds with optimum growth temperature (Topt) of 20-30 °C in the moderate climates, and those with Topt of 30-40 °C in the humid tropics. Table 1 presents an overview of selected filamentous fungi, the fermented foods in which they feature, their role in quality improvement, and some recent literature references. In the following sections these cases will be discussed in some detail, with a focus on the scientific questions of recent interest. Zygomycetes Among the Zygomycetes, mainly the order of Mucorales is of relevance for this chapter. Four genera, i.e., Actinomucor, Amylomyces, Mucor, and Rhizopus are of functional importance in a diversity of Oriental fungal fermented food products. The genus Amylomyces is considered by some (R. A. Samson, personal communication) as a domesticated form of Rhizopus. Amylomyces rouxii could not be discriminated from Rhizopus oryzae on the basis of 18S-28S rRNA because the amplified sequences were identical (Abe et al., 2004); A. rouxii could only be distinguished from R. oryzae because of its much higher number of chlamydospores in the aerial and substrate mycelium. On the other hand, the genotypes of Actinomucor, Rhizopus and Mucor were shown to be distinguishable as separate clusters (Han et al., 2004b). Actinomucor elegans (Han et al., 2001) and A. taiwanensis (Chou et al., 1988) are used as pure culture starters in the manufacture of Chinese fu-ru or sufu (Figure 1a).
