Whole Broth Processing

The concept of recovering a metabolite directly from an unfiltered fermentation broth is of considerable interest because of its simplicity, the reduction in process stages and the potential cost savings. It may also be possible to remove the desired fermentation product continuously from a broth during fermentation so that inhibitory effects due to product formation and product degradation can be minimized throughout the production phase (Roffler et al., 1984; Diaz, 1988).

Bartels et al. (1958) developed a process for adsorption of streptomycin on to a series of cationic ion-exchange resin columns directly from the fermentation broth, which had only been screened to remove large particles so that the columns would not become blocked. This procedure could only be used as a batch process. Belter et al. (1973) developed a similar process for the recovery of novobiocin. The harvested broth was first filtered through a vibrating screen to remove large particles. The broth was then fed into a continuous series of well-mixed resin columns fitted with screens to retain the resin particles, plus the absorbed novobiocin, but allow the streptomycete filaments plus other small particulate matter to pass through. The first resin column was removed from the extraction line after a predetermined time and eluted with methanolic ammonium chloride to recover the novobiocin.

Karr et al. (1980) developed a reciprocating plate extraction column (Fig. 10.33) to use for whole broth processing of a broth containing 1.4 g dm"3 of a slightly soluble organic compound and 4% undissolved solids provided that chloroform or methylene chloride were used for extraction. Methyl-iso-butyl ketone, diethyl ketone and iso-propyl acetate were shown to be more efficient solvents than chloroform for extracting the active compound, but they presented problems since they also extracted impurities from the mycelia, making it necessary to filter the broth before beginning the solvent extraction. Considerable economies were claimed in a comparison with a process using a Pod-bielniak extractor, in investment, maintenance costs, solvent usage and power costs but there was no significant difference in operating labour costs.

An alternative approach is to remove the metabolite continuously from the broth during the fermentation. Cycloheximide production by Streptomyces griseus has been shown to be affected by its own feed-back regulation (Kominek, 1975). Wang et al. (1981) have tested two techniques at laboratory scale for improving production of cycloheximide. In a dialysis method (Fig. 10.34), methylene chloride was circulated in a dialysis tubing loop which passed through a 10 dm"3 fermenter. Cycloheximide in the fermentation broth was extracted into the methylene chloride. It was shown that the product yield could be almost doubled by this dialysis-solvent extraction method to over 1200 fig cm"3 as compared with a control yield of approximately 700 fig cm"3. In a resin method, sterile beads of XAD-7, an acrylic resin, as dispersed beads or beads wrapped in an ultrafiltration membrane, were put in fermenters 48 hours after inoculation. Some of the cycloheximide formed in the broth is absorbed by the resin. Recovery of the antibiotic from the resin is achieved by solvents or by changing the temperature or pH. When assayed after harvesting, the control (without resin) had a bioactivity of 750 fig cm"3. Readings of total bioactivity (from beads and broth) for the bead treatment and the membrane-wrapped bead treatments

Karr Diagram

Fig. 10.33a. Diagram of a 0.35-m internal diameter reciprocating plate column (Karr et al, 1980).

Plate Distillation

A Fermenter B Extractor

1 Dialysis tubing

2 Pump Aqueous layer Solvent laysr Air inlet Air outlet

Fig. 10.34. Dialysis-extraction fermentation system (Wang et al 1981).

A Fermenter B Extractor

1 Dialysis tubing

2 Pump Aqueous layer Solvent laysr Air inlet Air outlet

Fig. 10.33a. Diagram of a 0.35-m internal diameter reciprocating plate column (Karr et al, 1980).

Fig. 10.34. Dialysis-extraction fermentation system (Wang et al 1981).

(a) Vacuum and flash fermentations for the direct recovery of ethanol from fermentation broths.

(b) Extractive fermentation (liquid-liquid and two-phase aqueous) for the recovery of ethanol, organic acids and toxin produced by Clostridium tetani.

(c) Adsorption for the recovery of ethanol and cy-cloheximide.

(d) Ion-exchange in the extraction of salicylic acid and antibiotics.

(e) Dialysis fermentation in the selective recovery of lactic acid, salicylic acid and cycloheximide.

Whole Broth Processing

Fig. 10.33b. Plan of a 23.8-m stainless-steel plate for a 25-mm diameter reciprocating plate test column (Karr et al., 1980).

were 1420 ¿u,g cm"3 and 1790 /xg cm"3 respectively.

Roffler et al. (1984) reviewed the use of a number of techniques for the in-situ recovery of fermentation products:

Hansson et al. (1994) have used an expanded adsorption bed for the recovery of a recombinant protein produced by E. coli directly from the fermentation broth. The protein was produced in high yields (550 mg dm"3) and > 90% recovery together with concentration (volume reduction) and removal of cells was achieved on the expanded bed. Affinity chromatography was used for further purification, and again an overall yield of > 90% obtained.

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  • christina
    What is whole broth processing?
    3 years ago
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    What is wholebroth processing?
    3 years ago
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    What is whole broth process?
    3 years ago

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