Contamination, Fermentation, Microbial

Although common electronic noses are generally not suitable for odour assessment, they can be successfully used in applications where the main components in the headspace are directly correlated with the property to be determined (e.g. quality of spice mixtures) or in cases where substances are formed and released into the headspace, for example owing to oxidation processes, fermentation, microbial contamination, thermal treatment, etc. 

Relative thermal resistance for the different types of microorganisms encountered in typical environments associated with fermentation broths is shown in Table 24-3. Bacterial spores are far more resistant to moist heat than are any other type oi microbial contaminants thus, a sterilization cycle based on the destruction of bacterial spores should destroy all life. 

Normally, fermentation processes can be classified depending on the objective of study. For example, in terms of products fermentation is divided into 4 types, namely, microbial cell, microbial enzyme, microbial metabolite and transformation process. If considering due to its contaminating conditions, it will be classified into 3 types septic, semi-septic and aseptic fermentation. However, in general, the fermentation processed are classified into 3 types as follows. 

A culture medium that is contaminated with 10 ° rn microbial spores of microorganisms will be heat-sterilized with steam of 121 °C. At 121 °C, the specific death rate of the spores can be assumed to be 3.2 mm [1]. When the contamination must be reduced to 1 in 1000 fermentations, estimate the required sterihzation time. 

The most obvious method of controlling microbial wine disorders is to prevent contamination of the wine. Yeasts which have been used for the alcoholic fermentation must be removed or inactivated before bottling. The same restriction applies to acetic- or lactic acid bacteria which may have entered the wine during or after fermentation. 

Biogenic amines can be found in processed meat products as a consequence of microbial activity related to the fermentation involved in their processing, but amines can be also found in poor-quality raw materials as a consequence of microbial contamination. Therefore the BA content in cooked meat (not fermented) products might serve as a useful indicator of the hygienic quality of the meat employed for its elaboration. However, this relationship for ripened meat products is rather complex, since the ability to produce BAs of the fermentative microflora need to be well known before limits can be set. According to the few studies performed on BAs in meat products,... 

In-pack pasteurisation. In-pack pasteurisation is normally reserved for dilutable products that are made without preservatives. Unless there are particular circumstances that demand a preservative-free product (e.g. manufacture of a certified organic product), preservatives should always be used in dilutables because of the way the drinks are used and stored. A dilutable without preservatives is very vulnerable to microbial contamination, which can lead to fermentation and possibly bottle bursting. Dilutables without preservative must be labelled to encourage refrigerated storage and short shelf life. 

For aerobic fermentations, air needs to be supplied continuously. Typical aeration rates for aerobic fermentation are 0.5 - 1.0 vvm (air volume per liquid volume per minute). This requires an enormous amount of air. Therefore, not only the medium but also the air must be free of microbial contaminants. All of the sterilization techniques discussed for medium can also be employed for air. However, sterilization of air by means of heat is economically impractical and is also ineffective due to the low heat-transfer efficiency of air compared with those of liquids. The most effective technique for air sterilization is filtration using fibrous or membrane filters. 

Another problem with conventional fermenters concerns foaming. In traditional systems, the introduction of large quantities of gas into the vigorously agitated fermentation liquor often produces great quantities of foam in the reaction vessel. Biological reactors are particularly susceptible to foaming because of the surfactant properties of most biomolecules. This foam severely limits the usable volume of the vessel and can render the fermentation process inoperable and microbially contaminated when the gas flow exit lines become filled with foam. All of these problems have a substantially adverse influence upon the yield and cost-eflectiveness of conventional fermentation processes. 

Addition of microorganisms and enzymes stimulates the biodegradation of xenobiotics in soils. Most efforts have been directed toward the use of bacterial inocula grown in large fermenters for the bioremediation of soils contaminated with PCP. Also, microbial immobilization on bark chips or their encapsulation in polyurethane or alginate, enhances their PCP-degrading ability as well as their resistance to PCP toxicity. 

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