Reference fermentation

Fig. 2. Ethanol productivity for untreated hydrolysate (black bar), fractions from strong anion-exchange resins (dark gray bars), fractions from weak anion-exchange resins (light gray bars), and reference fermentation (glucose added but no hydrolysate) (white bar). The maximum mean volumetric productivity of ethanol (Qe,0h) in g/ (L-h) is indicated above each bar.

Prior to the fermentations, the pH of the different hydrolysate samples was adjusted to 5.5 with NaOH (5 M). All fermentations were carried out under oxygen-limited conditions in 55-mL glass vessels containing 50 mL of medium of which 47.5 mL was hydrolysate (or, alternatively, an aqueous glucose solution for reference fermentations). The vessels were sealed with rubber stoppers and equipped with cannulas for outlet of C02. The hydrolysates were supplemented with nutrients as previously described (20). Fermentations of 35 g/L of glucose and nutrients but no hydrolysate were used for reference. The flasks were inoculated to an initial cell mass concentration of 2.0 g/L dry wt and incubated at 30°C with stirring. The fermentations were run for 36 h. Samples of 200 pL were taken after 0,2,4, 6, 8,10, 24, and 36 h. 

The maximum mean volumetric productivity of ethanol was obtained after 4 h in the reference fermentations. Therefore, the fermentability was evaluated by comparing the volumetric productivity, QEt0H (g/ [L-h]), of the different fermentations. QEt0H was calculated as the produced ethanol within the first 4 h of the fermentations divided by 4. 

Data about the physical characteristics of a bioreactor can provide only limited information. The complete characterization of a bioreactor requires additional studies involving biological test systems ( reference fermentations ). The fluid dynamics and rheological behavior of media are both directly and indirectly influenced by the presence of biological cells (Fiechter, 1978). Microbial processes whose growth or production kinetics are specifically dependent on changes in their medium or the reactor come into consideration as biological test systems (Karrer, 1978). Because of the central role of mass... 

During the 1980s, several distinctly different bioreactor designs (CSTR, Torus or horizontal loop bioreactor, jet loop bioreactor, compact loop bioreactor) were tested and compared at the Swiss Federal Institute of Technology, Zurich, by the group of Armin Fiechter. A reference fermentation with the strictly aerobic, non-fermentative, and glucose-insensitive yeast Trichosporon cutaneum on a defined medium was used [7]. The results of this study illustrate why the traditional CSTR, with multiple turbines, was and remains the most widely used reactor design. 

Welan is produced by 2is Pilcaligenes species (ATCC-31555) by aerobic fermentation, and marketed under the trade name BIOZAN (Merck and Co., Inc.) early reports also referred to it as S-130 (229). The polymer is stmcturaUy similar to geUan, sharing the same backbone sequence. It has an additional side group of an a-L-rhamnopyranosyl or an a-L-maimopyranosyl (Man ) unit linked (1— 3) to a P-D-glucopyranosyl unit in the backbone of the polymer ... 

Ivermectin is the catalytic reduction product of avermectin, a macroHde containing a spiroketal ring system. Two other related antibiotics having significantly different stmctural features and biological properties, moxidectin and milbemycin oxime, were more recentiy introduced into the market. Although these compounds have no antimicrobial activity, they are sometimes referred to as antibiotics because they are derived from fermentation products and have very selective toxicities. They have potent activity against worms or helminths and certain ectoparasites such as mites and ticks. 

The production of elfamycins is described in the references cited in Table 1. Fermentation yield improvements with aurodox (1, R = CH ) proved difficult because of feedback inhibition (48). Aurodox-resistant strains (49), however, responded positively to conventional mutagenic methods leading to yield increases from 0.4 to 2.5 g/L (50). Scale-up of efrotomycin (7, R = CH ) fermentations were found to be particularly sensitive to small changes in sterilization conditions of the oil-containing medium used (51). 

A Chinese pubHcation (47) with 17 references reviews the use of genetically engineered microorganisms for the production of L-ascorbic acid and its precursor, 2-KGA (49). For example, a 2-keto-L-gulonic acid fermentation process from sorbose has been pubUshed with reported yields over 80% (50). 

Whiskey. Whiskey refers to any alcohohc distiUate made from a fermented grain mash at less than 190° proof (95%) in such a manner that it possesses the taste, aroma, and characteristics generaUy attributed to whiskey. It is matured in new or used charred oak barrels. Whiskey can be further delineated by the cereal grains used and the maturation time and blending, if any. 

After 30 hours, the maximum and critical fermentation is underway and the pH must remain above 4.0 for optimal fermentation. However, accompanying bacterial contamination from various sources such as yeast contamination, improper cleaning procedures, slow yeast growth, or excessive temperatures can result in a pH below 4.0. The remaining amylase enzymes, referred to as secondary conversion agents, are inactivated and can no longer convert the dextrins to maltose. Under these circumstances, the fermentor pH continues to drop because of acid production of the bacteria, and the pH can drop to as low as 3.0. The obvious result is a low ethanol yield and quaUty deterioration. 

Early Industrial Enzymes. Enzymes were used in ancient Greece for the production of cheese (9). Early references to this are found in Greek epic poems dating from about 800 BC. Fermentation processes for brewing, baking, and the production of alcohol have been known since prehistoric times. 

While it is easy to add materials to a fermentation, removal is difficult. Membrane devices have been placed in the fermenter or in external recycle loops to dialyze away a soluble component. Cells release wastes or metabolites that can be inhibitory these are sometimes referred to as staling factors. Their removal bv dialysis has allowed cell concentrations to reach ten to one hundred times that of control cultures. 

There are many reactions in which the products formed often act as catalysts for the reaction. The reaction rate accelerates as the reaction continues, and this process is referred to as autocatalysis. The reaction rate is proportional to a product concentration raised to a positive exponent for an autocatalytic reaction. Examples of this type of reaction are the hydrolysis of several esters. This is because the acids formed by the reaction give rise to hydrogen ions that act as catalysts for subsequent reactions. The fermentation reaction that involves the action of a micro-organism on an organic feedstock is a significant autocatalytic reaction. 

From fermentation solutions of a Streptomyces aureofaciens mutant. Reference(s) ... 

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