Nutritional Requirements 129 supply both carbon and energy needs. Others need a variable number of additional organic compounds as nutrients. these additional organic nutri- ents are called growth factors and have a purely biosynthetic function, being equired as precursors of certain organic cell constituents that the organism is unable to synthesize. Most microorganisms that depend on organic carbon sources also require Co2 as a nutrient in very small amounts. In the fermentation of beet molasses to ethanol and glycerol, it was found that by manipulating several fermentation parameters, the ethanol yield (90.6%)and concentration(.5%v/v)remained essentially the same, while the glycerol concentration went from 8.3 g/l to 11.9 g/l. The CO, formation, however, was reduced! With glycerol levels over 12 g/l, the ethanol yield and concentration reduced with the CO2-formation near normal again. 15)In fermentations, the carbon source on a unit of weight basis may be the least expensiveraw material, however, quite often represents the largest single cost forraw material due to the levels required. Facultative organisms incorporate oughly 10% of substrate carbon in cell material, when metabolizing anaerobically, but 50-55%of substrate carbon is converted to cells with fully aerobic metabolism. Hence, if 80 grams per liter of dry weight of cells are required in an aerobic fermentation, then the carbon required in that fermen tation equals(80/2)(100/50)=80 grams of carbon. If this is supplied as the hexose glucose, with molecular weight 180 and carbon weight 72, then(80) 180)/72=200 gram per liter of glucose are required Carbohydrates are excellent sources of carbon, oxygen, hydrogen, and metabolic energy. They are frequently present in the media in concentrations higher than other nutrients and are generally used in the range of 0. 2-25% The availability of the carbohydrate to the microorganism normally depends upon the complexity of the molecule. It generally may be ranked as hexose>disaccharides> pentoses > polysaccharides Carbohydrates have the chemical structure of either polyhydroxyaldehydes or polyhydroxyketones. In general, they can be divided into three broad classes: monosaccharides, disaccharides and polysaccharides. Carbohy drates have a central role in biological energetics, the production of ATP. The progressive breakdown of polysaccharides and disaccharides to simpler sugars is a major source of energy-rich compounds. a during catabolism glucose, as an example, is converted to carbon dioxide, water and energy Enzymes catalyze the conversion from complex to simpler sugars. Three major interrelated pathways control carbohydrate metabolismNutritional Requirements 129 supply both carbon and energy needs. Others need a variable number of additional organic compounds as nutrients. These additional organic nutri￾ents are called growth factors and have a purely biosynthetic function, being required as precursors of certain organic cell constituents that the organism is unable to synthesize. Most microorganisms that depend on organic carbon sources also require CO, as a nutrient in very small amounts.['] In the fermentation of beet molasses to ethanol and glycerol, it was found that by manipulating several fermentation parameters, the ethanol yield (90.6%) and concentration (8.5% v/v) remained essentially the same, while the glycerol concentration went from 8.3 gA to 11.9 gA. The CO, formation, however, was reduced! With glycerol levels over 12 gA, the ethanol yield and concentration reduced with the C0,-formation near normal again.[5] In fermentations, the carbon source on a unit of weight basis may be the least expensive raw material, however, quite often represents the largest single cost for raw material due to the levels required. Facultative organisms incorporate roughly 10% of substrate carbon in cell material, when metabolizing anaerobically, but 50-55% of substrate carbon is converted to cells with fully aerobic metabolism. Hence, if 80 grams per liter of dry weight of cells are required in an aerobic fermentation, then the carbon required in that fermen￾tation equals (80/2) (100/50) = 80 grams of carbon. Ifthis is supplied as the hexose glucose, with molecular weight 180 and carbon weight 72, then (80) (1 80)/72 = 200 gram per liter of glucose are required. Carbohydrates are excellent sources of carbon, oxygen, hydrogen, and metabolic energy. They are frequently present in the media in concentrations higher than other nutrients and are generally used in the range of 0.2-25%. The availability of the carbohydrate to the microorganism normally depends upon the complexity of the molecule. It generally may be ranked as: hexose > disaccharides > pentoses > polysaccharides Carbohydrates have the chemical structure of either polyhydroxyaldehydes or polyhydroxyketones. In general, they can be divided into three broad classes: monosaccharides, disaccharides and polysaccharides. Carbohy￾drates have a central role in biological energetics, the productionofATP. The progressive breakdown of polysaccharides and disaccharides to simpler sugars is a major source of energy-rich compounds.['] During catabolism, glucose, as an example, is converted to carbon dioxide, water and energy. Enzymes catalyze the conversion from complex to simpler sugars. Three major interrelated pathways control carbohydrate metabolism: