Filamentous Fungi

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Compared to yeasts, filamentous fungi have been used less frequently for bioconversion of distillery wastes. The reasons might be that they are slower growing and more susceptible to infection. However, filamentous fungi have some advantages as they produce a series of extracellular hydrolytic enzymes and are therefore able to exploit complex carbohydrates without prior hydrolysis; this property enables them to grow in starch and cellulose substrates. The second advantage is in their filamentous morphology that allows separation of the biomass by simple filtration. Compared to yeasts, filamentous fungi have lower sensitivity to variations in temperature, pH, nutrients, and aeration, and they also have a lower nucleic acid content in the biomass (Araiijo et al. 1977). Various species of fungi were used for distillery stillage fermentations, among them Aspergillus spp. being the most popular ones. Aspergillus oryzae (Araiijo et al. 1977; De Lamo and De Menezes 1978) and Aspergillus niger (De Lamo and De Menezes 1978) were selected out of several filamentous fungi due to their high biomass yield, rapid filtration, and substantial COD reduction in cane molasses stillage. A. niger was also suitable for bioconversion of rice spirit

(Yang and Lin 1998). Aspergillus awamori var. kawachi and Aspergillus usami mut. shirousami were used for byconversion of distillery waste of a Japanese alcohol beverage, shochu (Kidaetal. 1995;Morimuraetal. 1991; 1992; 1994a). Filamentous fungi were chosen for conversion of stillage, due to their texture, protein profile, and easy harvesting, and Aspergillus phoenicis was the most promising among isolates from contaminated stillage (De Gonzales and De Murphy 1979). Aspergillus species were also suitable for converting fruit based distillery stillages, A. niger biomass produced in vinasse from raisin brandy has a good amino acid content (Aran 1977; Yazicioglu et al. 1980), while cellulolytic Aspergillus species were very effective in improving filtration and reducing COD of apple brandy slops (Friedrich et al. 1983; 1986; 1987; Gunde-Cimerman et al. 1986; Perdih et al. 1991). Many other fungi proved promising in treating and converting different kinds of stillages. For example, Penicillium species were chosen for utilization of white wine vinasse, due to their good adaptation, utilization of the medium, and development at low pH values (Magny et al. 1977). Penicillium oxalicum produced the highest biomass amount with high protein content in raisin brandy vinasse (Aran 1977; Yazicioglu et al. 1980). Geotrichum candidum was selected from a variety of soil microorganisms for whisky stillage conversion (Quinn and Marchant 1979a,b; 1980) and for decolorizing molasses stillage, since it was able to reduce the phenolic compounds (Fitzgibbon et al. 1995; 1998). Compared to several yeasts, molds, and bacteria, Paecilo-myces varioti was very effective in aerobic treatment (Nudel et al. 1987) and for producing single cell protein (SCP) from cane molasses stillage (Azzam and Heikel 1989; Cabib et al. 1983). Gliocladium deliquescens performed best among different fungi in rum distillery wastewater (Rolz et al. 1975). Acremonium fusidioides was isolated from soil, treated with stillage, and it clarified and decolorized the effluent and produced the highest biomass amount (Rosalem et al. 1985). Trichoderma species were successfully utilized in aerobic treatment of cane molasses stillage (Nudel et al. 1987) and for bioconversion of fruit distillery slops; the fungi degraded raw fibers, exhibited high cellulolytic activity, and produced high protein content in the biomass (Friedrich et al. 1986; Perdih et al. 1991). Fusarium moniliforme grown in vinasse from raisin brandy produced high lipid biomass (Aran 1977; Yazicioglu et al. 1980). Myrothecium verrucaria was effective in reducing organic substances in apple distillery slop as well as in improving its filterability (Friedrich et al. 1986). Aureobasidium sp. could produce a biopolymer pullulan from corn condensed distiller's solubles (Leathers and Gupta 1994). Among the microorganisms tested for the treatment and bioconversion of shochu, a Japanese distilled spirit, zygomycetous fungi, Absidia atrospora and Gongronella butleri strains were selected and used in a cost effective procedure for chitosan production in the wastewater (Yokoi et al. 1998).

The development of basidiomycetous fungi (mushrooms) in submerged culture is interesting because of their probable suitability as cheap substitutes for mushroom fruiting bodies in certain kinds of food. Falanghe (1962) investigated the suitability of stillage for growing mushroom mycelia as a source of protein and fat. Among ten strains cultivated in submerged conditions, Agaricus campestris and Boletus indecisus were chosen as the two most suitable. A. campestris was more effective in producing mycelial protein content. B. indecisus, however, exhibited a greater ability for mycelial production. The dried mycelia had a pleasant slight flavor and they seemed to have adequate characteristics for improving foods; their growth in pellet form enabled easy separation from the medium. In apple distillery slop, Phanerochaete chrysosporium grew successfully; it reduced the amount of fiber and improved protein content in the biomass (Friedrich et al. 1986). Coriolus versicolor and P. chrysosporium could be used for reducing pollution and decolorizing the diluted molasses spent wash (Fitzgibbon et al. 1995; 1998). Other white rot fungi, Funalia trogii and Trametes versicolor were used for producing plant growth hormones in vinasse from molasses and, in addition, partial COD and color were removed (Ytirekli et al. 1999).

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