POST-FERMENTATION GROWTH

Both yeast and bacteria are capable of utilizing the acid in production of diacetyl, acetoin, and acetic acid (see Fig. 1-11 A). Diacetyl resulting from yeast activity is typically below threshold, ranging from 0.2 to 0.3 mg/L. Its familiar buttery properties are perceived at higher concentrations and result from post-fermentation growth of LAB. Depending on the intrinsic... 

Long-term chemical changes also take place in the maturation vessel such as esterification and certain reductions. During the post-fermenting treatment of beer it is necessary to promote clarification of the beer and, by stabilizing treatment, ensure that turbidity due to chemical precipitation or growth of micro-organisms does not occur. 

Depending on the stage of yeast growth, prepare the appropriate dilutions using 9-mL isotonic saline dilution blanks. For example, in monitoring starter tanks, initial lO -lO" dilutions may be required to obtain countable numbers, whereas post-fermentation counts may be made directly without prior dilution. 

Considered to be spoilage microorganisms in winemaking (Drysdale and Fleet, 1988 Du Toit and Pretorius, 2002), growth of acetic acid bacteria results in oxidation of ethanol to acetic acid (the process of ace-tification). In addition, other odor- and flavor-active metabolites as well as polysaccharides including dextrans and levans may he formed (Colvin et al., 1977 Tayama et al., 1986). The latter can create problems during post-fermentation clarification and stabihty. 

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). 

This study demonstrated that the Pu-Erh tea contained lovastatin in a low, but yet detectable amount. The aqueous extract of Pu-Erh tea (PET) inhibited cholesterol biosynthesis in cultured human hepatoma cells (Hep G2). PET did not affect post-mevalonate events in the cholesterol pathway, since the incorporation of labeled mevalonate into cholesterol was not affected. Direct evidence to support the occurrence of lovastatin in PET was based on extensive purification and identification of lovastatin in its lactone form by mass spectrometry. To enrich lovastatin, PET was solvent extracted to recover lovastatin in lactone form. The content of lovastatin in Pu-Erh tea varied greatly among different batches. The situation is not unexpected, since the preparation procedure of Pu-Erh tea involves natural fermentation. The growth of Aspergillus and production of lovastatin in Pu-Erh tea during the fermentation and storage is not under control. 

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