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#fermentation process

3 public questions tagged with this topic.

Basic Applied Biology

Batch fermentation is characterized by:

Batch fermentation represents simplest closed system operation where all nutritional components, medium, precursors and inoculum are added at beginning, vessel sterilized, and no further input or output occurs except for aeration gases, acid-base addition for pH control and occasional sampling until harvest after complete cycle. Microbial population traverses classic growth curve including lag adaptation with enzyme induction, exponential phase where Monod kinetics mu equals mu-max times S over Ks plus S governs, stationary phase where nutrient exhaustion and organic acid accumulation limit growth, and death phase. Mass balance applies only to initial volume, simplifying sterility validation, instrumentation and batch record traceability per lot. Advantages include flexible product changeover, reduced contamination cross-over and suitability for secondary metabolites like penicillin that require full physiological differentiation. Downsides encompass downtime for cleaning and sterilization, lower volumetric productivity compared to continuous systems and initial substrate inhibition at high sugar concentrations above 100 g per L causing osmotic stress and overflow metabolism.

Ref: Stanbury et al. Principles of Fermentation Technology 3rd ed. Ch 3 Batch culture; NCBI Bookshelf NBK 202 growth kinetics.

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Basic Applied Biology

Solid state fermentation is best suited for production of:

Solid state fermentation employs microbial growth on moist solid particles in near absence of free water, with water activity maintained around 0.6 to 0.9 and moisture bound within matrix pores. This environment mimics natural habitats of filamentous fungi where aerial mycelial penetration and sporulation are favored. Porous lignocellulosic substrates like wheat bran, rice husk, sugarcane bagasse, and soybean meal provide carbon, nitrogen and physical anchorage. Low water availability reduces bacterial contamination risk, limits catabolite repression, lowers effluent generation and enhances oxygen diffusion at substrate-air interface, favoring secretion of extracellular enzymes such as cellulases, amylases, glucoamylases, pectinases, xylanases and proteases by Aspergillus niger, Trichoderma reesei and Rhizopus oligosporus. Heat removal and mass transfer gradients remain challenges but high volumetric productivity, product stability and simplified downstream extraction make SSF economically attractive. In contrast, diffusible small molecules like penicillin and citric acid requiring precise dissolved oxygen and pH control are better produced in submerged fermentation with mechanically agitated bioreactors.

Ref: Pandey et al. Biotechnology Advances 2000 Solid state fermentation review; Stanbury et al. Principles of Fermentation Technology Ch 7.

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