Bacteria and fermentation

Silage additives can be classified into two main types fermentation stimulants, such as sugar-rich materials, inoculants and enzymes, which encourage the development of lactic acid bacteria and fermentation inhibitors, such as acids and formalin, which partially or completely inhibit microbial growth. 

Lactose intolerance Several studies have shown that lactose-intolerant individuals suffer fewer symptoms if milk in the diet is replaced with fermented dairy products. The mechanisms of action of lactic acid bacteria and fermented dairy products include the following lower lactose concentration in the fermented product due to lactose hydrolysis during fermentation high lactase activity of bacterial preparations used in production and increased active lactase enzyme entering the small intestine with the fermented product or within the viable bacteria. 

Lin, T. Y. Chang Chien, M. F. (2007). Exopolysaccharides production as affected by lactic acid bacteria and fermentation time. Food Chemistry, 100,1419-1423. 

Sulfur Dioxide and Sulfites. Sulfur dioxide [7446-09-5], SO2, sodium bisulfite [15181-46-1], NaHSO, and sodium metabisulfite [23134-05-6] ate effective against molds, bacteria, and certain strains of yeast. The wine industry represents the largest user of sulfites, because the compounds do not affect the yeast needed for fermentation. Other appHcations include dehydrated fmits and vegetables, fmit juices, symps and concentrates, and fresh shrimp (79). Sulfites ate destmctive to thiamin, and cannot be used in foods, such as certain baked goods, that ate important sources of this vitamin. 

Primitive people very likely encountered vinegar-like Hquids in hoUows in rocks or downed timber into which berries or fmit had fallen. Wild yeasts and bacteria would convert the natural sugars to alcohol and acetic acid. Later, when eady peoples had learned to make wines and beers, they certainly would have found that these Hquids, unprotected from air, would turn to vinegar. One can postulate that such eady vinegars were frequendy sweet, because the fmit sugars would have been acted on simultaneously by both bacteria and yeast. Only since the middle 1800s has it been known that yeast and bacteria are the cause of fermentation and vinegar formation. 

Manufacturing procedures of riboflavin have also appeared using Saccharomjces bacteria, eg, fermentation with a purine-independent S. reverse mutant (61) and with S. cerevisiae NH-268 (62) produced 2.79 g/L and 4.9 g/L, respectively. 

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. 

The bacteria and bacterial components needed for the manufacture of bacterial vaccines are readily prepared in laboratory media by well-recognized fermentation methods. The end-product of the fermentation, the harvest, is processed to provide a concentrated and purified vaccine component that may be conveniently stored for long periods or even traded as an article of commerce. 

Nonvolatile Nitrosamines In Tobacco. A method which we developed several years ago for the analysis of tobacco-specific nitrosamines (TSNA 31) involves extraction of tobacco with buffered ascorbic acid TpH 4.5) followed by partition with ethyl acetate, chromatographic clean-up on silica gel, and analysis by HPLC-TEA (Figure 9). Results obtained with this method for a large spectrum of tobacco products (Table IV), strongly support the concept that the levels of nitrate and alkaloids, and especially the methods for curing and fermentation, determine the yields of TSNA in tobacco products. Recent and as yet preliminary data from snuff analyses indicate that aerobic bacteria play a role in the formation of TSNA during air curing and fermentation. 

Kolb S, S Seeliger, N Springer, W Ludwig, B Schink (1998) The fermenting bacterium Malonomonas rubra is phylogenetically related to sulfur-reducing bacteria and contains a c-type cytochrome similar to those of sulfur and sulfate reducers. SystAppl Microbiol 21 340-345. 

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