Fermentable substrates

Sucrose is often used as a decorative agent to impart a pleasing appearance to baked goods and confections (36). In jams and jeUies, sugar raises osmotic pressure and lowers water activity to prevent spoilage (18). Sucrose is a fermentation substrate for lactic acid in cultured buttermilk (40) and lowers the freezing point of ice cream and other frozen desserts to improve product mouthfeel and texture. 

More recently, interest has developed in the use of enzymes to catalyze the hydrolysis of cellulose to glucose (25—27). Domestic or forest product wastes can be used to produce the fermentation substrate. Whereas there has been much research on alcohol fermentation, whether from cereal grains, molasses, or wood hydrolysis, the commercial practice of this technology is primarily for the industrial alcohol and beverage alcohol industries. About 100 plants have been built for fuel ethanol from com, but only a few continue to operate (28). 

Lactose is mainly used as a fermentation substrate for lactic acid bacteria in dairy products, such as yogurt and cheese. These bacteria break down lactose into lactic acid, which solidifies the milk, and creates an acid environment that favors the benign lactic acid bacteria over those that are more harmful. 

Pluske J.R., Siba P.M., Pethick D.W., Durmic Z., Multan B.P. and Hampson DJ. (1996). The incidence of swine dysentery in pigs can be reduced by feeding diets that limit the amount of fermentable substrate entering the large intestine . J Nutr, 126, 2920-2933. 

Polyphenols bound to DF can account for a substantial part of total PPs in foods and beverages. These polyphenols are not bioavailable in the human upper intestine and reach the colon, where they become fermentable substrates for bacterial microflora, along with the DF. 

As a result, the partial breakdown of the organic matter by fermentation yields organic products with a low molecular weight, e.g., VFAs, along with C02. Compared with the aerobic respiration, the fermentation is inefficient however, these fermentation products can to some extent, and in addition to fermentable substrate, be used by the sulfate-reducing bacteria that make use of sulfate as the terminal electron acceptor (Nielsen and Hvitved-Jacobsen, 1988). In the absence of sulfate, the methanogenic bacteria utilize the low molecular... 

Odour will return in treated slurry as a result of post treatment fermentation. The concentration of readily fermentable substrates, measured as BOD5, provide an indicator of this problem. In continuous culture without oxygen limitation the BOD5 can be described by a model derived from the Monod (13) model of microbial growth (14). The supernatant BOD5 (g/1) from treatment at 15 to 45°C, was described by equation 3 and the whole BOD5 by equations 4 and 5(15). 

If the slurry is to be stored after treatment the residual, readily-fermentable substrate requires consideration. As treatment time is extended the total BOD5 falls to a minimum value of about 20% of its value in raw slurry after treatment at 15°C, or 15% after treatment at higher temperatures, equations 4 and 5. It may be postulated that the difference between the actual residual total BOD5 and its minimal value will provide a more accurate measure of the residual, readily-fermentable substrate and hence an... 

The next step of the biotechnical sequence, yeast fermentation, is of the utmost importance to the chemistry of winemaking as well as to the formation of flavor substances. We have investigated this previously using 14C-tagged compounds (16). Amino acids, for example, enter the yeast fermentation with a quasi biochemical valence with regard to the formation of metabolic side products like alcohols and esters. In that respect, the composition of the fermentation substrate, the grape must, is highly important to the formation of aroma substances by yeasts. 

Thayer, D. W. Woody Plants A Renewable Fermentation Substrate, ... 

Taking the idea of yeast recovery one step further is continuous fermentation. This incorporates a vessel or vessels inoculated with yeast through which the fermentable substrate is passed continuously. The flow is designed to ensure that all the sugar is fermented before it exits the final fermenter as beer. This beer is clarified to remove any entrained yeast cells and a percentage of the yeast is recycled back into the system. 

Starch-derived sweeteners provide a highly fermentable substrate for many industrial applications. The ability of yeast to ferment starch-derived syrups is directly... 

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