Microbial load

Kistemann T, ClaPen T, Koch C et al (2002) Microbial load of drinking water reservoir tributaries during extreme rainfall and runoff. Appl Environ Microbiol 68 2188-2197... 

Condensation will wash contaminating organisms onto the surface of the bulk phase where, especially if the vessel remains unstirred for some time, dilution of the surface layer, and hence the biocide in it, can allow profuse microbial growth to occur. When mixing recommences, such a high microbial loading will enter the bulk phase and may overwhelm a biocide. 

Table 12.1. Microbial loads predominant in some fresh fruits and vegetables...

Sanitization Reduction of microbial load on an inanimate surface to a level considered acceptable for public health purposes... 

Heat the suspension in a covered container for 30 minutes at 68°C (maintain 68°C for 30 minutes) this is a pasteurizing step to reduce microbial load. 

In the broadest sense, stability of emulsions should be defined as maintenance of an initial state that was attained after homogenization of the two (or more) liquids (Sjoblom, 1996). The initial state of the emulsion can be defined by a set of internal parameters. The primary parameters used to describe the state of an emulsion are droplet size distribution and concentration, since the bulk properties of emulsions such as color, texture, and taste are primarily a function of these two colloidal parameters (McClements, 1999). In selected cases it may be necessary to include additional parameters such as pH and microbial load to further define the initial state of the emulsion. 

In less developed countries, water treatment becomes an essential prerequisite where microbial loading could provide cause for concern. It is necessary for a full water treatment to be effective and to ensure the wholesomeness of water supplies for boiling ptuposes. 

Typical flash pasteurisation operations for fruit juices and nectars will employ a plate pasteuriser with heat recovery and final product cooling. Typical flash pasteurisation conditions will use temperatures between 85 and 95°C with holding times varying between 15 and 60 s. Selection of the appropriate conditions will depend on the product, including the level of microbial load pre-pasteurising. If enzyme deactivation is required as well as microbial removal then a temperature between 90 and 95°C will normally be used. At these temperatures, holding times are normally reduced to around 15 s. 

Figure 4 Survivor curves showing the effect of decreasing the microbial load (A) from 106 to 102 on the time required to achieve a probability of nonsterility (B) of 10 6.

Equations that apply for determining log reductions or survival probabilities are Eq. (11) and Eq. (12), respectively. Information that must be known prior to initiating biological validations include the D value of the biological indicator to be used, the change in its heat resistance as temperature is changed (Z value), and the presterilization microbial load on the commodity being steri-... 

If it is assumed that the radiation sterilizer equipment and facilities have been qualified and microbiological studies have been conducted as previously outlined, the next step in the validation process is the complete evaluation of the radiation sterilization cycle. Tests are conducted to determine the effect of minimum and maximum product density on the ability of the minimum or nominal radiation dose—determined during the microbiological studies to produce a given log reduction in the biological indicator population—to sterilize the load. For example, it was found that a 0.2-Mrad dose of cobalt-60 will produce a 1-log reduction in the population of B. pumilus. The microbial load of a one-package polyvinyl chloride (PVC) device (intravenous administration site) was estimated to be approximately 1000. A probability of a nonsterility level of 10 6 is desired, therefore theoretically, the minimum dose necessary to produce a 9-log reduction in the microbial population is 1.8 Mrad. 

Because sap is a perishable product, it is generally processed relatively soon after collection to minimize microbial contamination and the accompanying reduction in syrup quality. Sap is often filtered and UV-sterilized after collection to reduce microbial loads in order to maintain sap quality. Ozone treatment, although useful in water treatment, does not appear to be effective in maple applications, presumably due to the strong protective effect of sugars on microbial populations (Labbe et al, 2001). 

---