Abstract
Pellet formation of filamentous fungi in submerged culture is an imperative topic of fermentation research. In this study, we report for the first time the growth of filamentous ascomycete fungus, Neurospora intermedia in its mycelial pellet form. In submerged culture, the growth morphology of the fungus was successfully manipulated into growing as pellets by modifying various cultivation conditions. Factors such as pH (2.0–10.0), agitation rate (100–150 rpm), carbon source (glucose, arabinose, sucrose, and galactose), the presence of additive agents (glycerol and calcium chloride) and trace metals were investigated for their effect on the pellet formation. Of the various factors screened, uniform pellets were formed only at pH range 3.0–4.0, signifying it as the most influential factor for N. intermedia pellet formation. The average pellet size ranged from 2.38 ± 0.12 to 2.86 ± 0.38 mm. The pellet formation remained unaffected by the inoculum type used and its size showed an inverse correlation with the agitation rate of the culture. Efficient glucose utilization was observed with fungal pellets, as opposed to the freely suspended mycelium, proving its viability for fast-fermentation processes. Scale up of the pelletization process was also carried out in bench-scale airlift and bubble column reactors (4.5 L).
Highlights
Filamentous fungi are widely used industrial microorganisms that contribute to the global economy via production of a plethora of important products such as antibiotics, enzymes, organic acids, human/animal food or pharmaceutical product (Liao et al 2007; Prajapati et al 2014; Zhang and Zhang 2015)
The edible ascomycete filamentous fungus N. intermedia, studied in this work has not been reported to grow as pellets, to the best of our knowledge
Five different factors as pH (2.0, 4.0, 5.5, 7.0, 9.0 and 10.0), agitation rate (100, 125 and 150 rpm), carbon source, presence of additive agents and trace metals were investigated for their effect on the pelletization process
Summary
Filamentous fungi are widely used industrial microorganisms that contribute to the global economy via production of a plethora of important products such as antibiotics, enzymes, organic acids, human/animal food or pharmaceutical product (Liao et al 2007; Prajapati et al 2014; Zhang and Zhang 2015). The ascomycete filamentous fungi Neurospora intermedia studied in this work has been traditionally used for the preparation of an indigenous Indonesian food, oncom. N. intermedia possess high ethanol fermenting capability compared to other edible filamentous fungi such as Aspergillus oryzae, Fusarium venenatum, Monascus purpureus, Rhizopus sp. A potential solution to overcome the problems associated with the filamentous growth is to obtain growth in the form of pellets. Filamentous fungi can be grown in submerged cultures in several different morphological forms such as free suspended mycelia (with typical diameters of 2–18 μm), or as mycelial clumps or as pellets (Liao et al 2007; Ward 2012). Pellet formation of the filamentous fungi in submerged cultivation has attracted the attention of researchers and industrial engineers since decades. Pellet morphologies have been classified into three different groups encompassing, (a)
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