Surface fermentation

The effectiveness of microbial cellulose production depends mainly on the strain, the composition of the culture medium (the C source used being very significant), the fermentation temperature, oxygen supply, and the implementation of static or agitated systems. The cost of the media is an important factor for cost-effective BNC production, and therefore its composition and volume as well as the fermenter surface area should all be considered. 

By approximately 8 weeks after birth, the mminant has developed a fully functional mmen capable of extensive fermentation of feed nutrients (4). The rate of development of the mminal environment depends on the amount of milk consumed by the neonate in relation to its growth requirements, the avadabihty and consumption of readily digestible feedstuffs, and the physical form of the feedstuffs (4). The mmen develops much faster with hay than with milk (36). Concentrates, ie, high cereal grain diets, increase the absorptive surface of the mmen but mminal size and musculature develops much more slowly with a concentrate diet than with a forage diet (4). 

Lactic Acid B cteri. The lactic acid bacteria are ubiquitous in nature from plant surfaces to gastrointestinal tracts of many animals. These gram-positive facultative anaerobes convert carbohydrates (qv) to lactic acid and are used extensively in the food industry, for example, for the production of yogurt, cheese, sour dough bread, etc. The sour aromatic flavor imparted upon fermentation appears to be a desirable food trait. In addition, certain species produce a variety of antibiotics. 

In 1973, a multistage surface-fermentation process was patented in Japan for the production of acetic acid (42) eight surface fermenters were connected in series and arranged in such a way that the mash passed slowly through the series without disturbing the film of yAcetobacter on the surface of the medium. This equipment is reported to produce vinegar of 5% acidity and 0.22% alcohol with a mean residency time in the tanks of 22 h. 

A commercial bacterial cellulose product (CeUulon) was recently introduced by Weyerhaeuser (12). The fiber is produced by an aerobic fermentation of glucose from com symp in an agitated fermentor (13,14). Because of a small particle diameter (10 P-m), it has a surface area 300 times greater than normal wood cellulose, and gives a smooth mouthfeel to formulations in which it is included. CeUulon has an unusual level of water binding and works with other viscosity builders to improve their effectiveness. It is anticipated that it wiU achieve GRAS status, and is neutral in sensory quaUty microcrystaUine ceUulose has similar attributes. 

Fermentation. The microbial production of citric acid on a commercial scale was begun in 1923 utilizing certain strains yispergillus nigerio produce citric acid on the surface of a sucrose and salt solution. This tray fermentation technique is still used today, although it is being replaced by a submerged process known as deep tank fermentation (14—22). 

Until about 1950, the predominant method of producing industrial enzymes was by extraction from animal or plant sources by 1993, this accounts for less than 10%. With the exception of trypsin, chymosin, papain [9001 -73-2J, and a few others, industrial enzymes are now produced by microorganisms grown in aqueous suspension in large vessels, ie, by fermentation (qv). A smaH (5%) fraction is obtained by surface culture, ie, soHd-state fermentation, of microorganisms (13). 

Interfacial Phenomena These can significantly affect overall mass transfer. In fermentation reactors, small quantities of surface-active agents (especially antifoaming agents) can drastically reduce overall oxygen transfer (Aiba et al., op. cit., pp. 153, 154), and in aerobic... 

For MPN determination, sterile pipettes calibrated in 0.1-ml increments are used. Other equipment includes sterile screw-top dilution bottles containing 99 ml of water and a rack containing six sets of five lactose broth fermentation tubes. A sterile pipette is used to transfer 1.0-ml portions of the sample into each of five fermentation tubes. This is followed by dispensing 0.1 ml into a second set of five. For the next higher dilution (the third), only 0.01 ml of sample water is required. This small quantity is very difficult to pipette accurately, so 1.0 ml of sample is placed in a dilution bottle containing 99 ml of sterile water and mixed. The 1.0-ml portions containing 0.01 ml of the surface water sample are then pipetted into the third set of five tubes. The fourth set receives 0.1 ml from this same dilution bottle. The process is then carried one more step by transferring 1.0 ml from the first dilution bottle into 99 ml of water in the second for another hundredfold dilution. Portions from this dilution bottle are pipetted into the fifth and sixth tube sets. After incubation (48 h at 35 C), the tubes are examined for gas production and the number of positive reactions for each of the serial dilutions is recorded. 

Chloramphenicol may be prepared by fermentation or by chemical synthesis. The fermentation route to chloramphenicol is described in U.S. Patents 2,4B3,B71 and 2,4B3,B92. To quote from U.S. Patent 2,4B3,B92 The cultivation of Streptomyces venezuelae may be carried out in a number of different ways. For example, the microorganism may be cultivated under aerobic conditions on the surface of the medium, or it may be cultivated beneath the surface of the medium, i.e., in the submerged condition, if oxygen is simultaneously supplied. 

This material was made up with distilled water to provide 41 g per liter, and the mixture was adjusted to pH 7.0 with potassium hydroxide solution. To the mixture were added per liter 5.0 g of calcium carbonate and 7.5 ml of soybean oil. 2,000 ml portions of this medium were then added to fermentation vessels, equipped with stirrers and aeration spargers, and sterilized at 121°C for 60 minutes. After cooling the flasks were inoculated with a suspension of strain No. ATCC 11924 of Streptomyces lavendulae, obtained from the surface of agar slants. The flasks were stirred for 4 days at 28°C at approximately 1,700 rpm. At the end of this period the broth was found to contain cycloserine in the amount of about 250 C.D.U./ml of broth. The mycelium was separated from the broth by filtration. The broth had a pH of about 7.5. Tests showed it to be highly active against a variety of microorganisms. 

Figure 6.4 Stylised representation of changing parameters and penicillin production in cultures of Penldlllum notatum, grown as a surface culture on Czapek-Dox medium (adapted from Hockenhull DJ-D "Production of Antibiotics by Fermentation in Essays in Applied Microbiology edited by Norris J R Richmond M H 1981. John Wiley Sons Ltd Chichester).

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