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Published byHoward Thornton Modified over 8 years ago
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Selected Products of Bioprocessing digging a bit deeper
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Citric acid 1923, first commercial production by fermentation today, 99% produced via fermentation Mexico and S. America extract from lemons (7-9%) 250,000 Tons/year in 220 m 3 fermentors (about 6 m cube)
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Producers USA: 180,000 Tons/yr Pfizer Miles Lab Inc. Sturge Ltd of Birmingham (UK)
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Citric acid applications 60% used in food and beverage: fruit juice, candy, ice cream, marmalade enhances and preserves flavors 10% in pharmaceutical manufacture: blood preservative, iron citrate (Fe supplement), cosmetics 25% in chemical industry: antifoam, softener, textiles, metalurgical (chelator), replacement of polyphosphates in detergents
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Citric acid biochemistry structure produced by fermentation of carbohydrates
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glucose to pyruvate
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Citric acid cycle key to citrate overproduction
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Microbial culture Aspergillus niger (fungus)
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Source of glucose? beet molasses potato starch (fungi produce amylases) sucrose
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Types of culture stationary or surface culture submerged culture (most common) solid state, continuous, multi- stage culture
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Surface culture 8-12 days, but mycelium can be reused
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Submerged process 3-5 days
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Solid state bit of a mess! porous solid materials (sugarcane bagasse, potato or beet pulp... mixed with medium and inoculated 6-7 days fermentation, then extracted with water
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Culture conditions high initial sugar concentration important: 15-18% (A. niger likes it like that!) growth phase, followed by production phase pH from 1.4 to 3, to suppress contaminants and suppress oxalic acid production (by-product)
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More tedious conditions? inoculum is spores or mycelium older spores (>8 days) don’t germinate very well oxygen demand often larger than supply sometimes oxygen enriched air used but $$ly if O 2 limiting, bugs can metabolize citric acid (not helpful) agitation gets the acid away from the mycelium (inhibition) T opt = 25-30 o C 7-10 days for surface, and 4-5 days for submerged cultures
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Any genetic improvements? few mutation and selection of spores (shotgun approach) difficult as no efficient screening protocol for citrate overproducers
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