Decimal reduction value

By 1965, 25 kGy was quoted [8] as being the accepted dose of radiation for sterilizing disposable medical equipment in most countries except Denmark, where 45 kGy was being claimed to be necessary. As a consequence there was a flurry of scientific activity to validate the choice of 25 kGy retrospectively. Much of this work was done in laboratory studies with the most radiation-resistant microorganism then known, the spore of Bacillus pumilus E601 and centered on the determination of inactivation factors. An inactivation factor is the number of decimal reduction values (Dig-values) delivered by a particular dose. For these spores irradiated in air the 0 q was consistently found to be 1.7 kGy, hence the inactivation factor was 15. This implies that an SAL of belter than 10 can be achieved for items contaminated with up to 10 spores of these microorganisms per item, and by inference for higher bioburdens of less radia-... 

D-value (decimal reduction time, DRT) is the time in minutes required to destroy 90% of a population of cells. The D-value has little relevance to the sterilization of medicines for injection, surgical instruments or dressings, where a process designed to kill all living spores must be developed. The D-value is used extensively in the food industry. 

The use of ionizing irradiation on fruits and vegetables has not been intensively studied, but a few experiments have suggested that irradiation has potential for such an application (Allende et al., 2006 Zhang et al., 2006). Results from Buchanan et al. (1998) indicated that low-dose irradiation could easily eliminate E. coli 0157 H7 from fresh apple juice, but they also showed that acid-adapted strains needed higher doses of irradiation in order to obtain a 5 D inactivation in juice (73-value decimal reduction time, i.e. the amount of time it takes at a certain temperature to kill 90% of the organisms being studied (Wikipedia, 2006)). In experiments where sprouts were irradiated... 

The increased incidence of food-borne diseases from shellfish contaminated with Vibrio species have brought forward renewed interest in irradiation of shellfish and other seafood. Results are very promising for clams and oysters without killing the molluscs [65]. The radiation decimal reduction dose (Dio) determined for Vibrio cholerae 01 biotype El Tor inoculated into various molluscs was 0.14 kGy [66]. Similar radiation sensitivity of this organism was found in inoculated fish fillets and shrimp tails [67]. The radiation dose to eliminate as high as 10 CFU/g Vibrio spp. in oysters was 1.2 kGy [68]. The radiation Dio value for V. cholerae 01 biotype El Tor in marine snails was 0.11 kGy [69]. 

A detailed discussion of these kinetics is out of place in this present text but the above equation does allow some simplified considerations to be made. For example, a useful parameter easily derived is the decimal reduction time, D, for a mixed or single culture is the time it takes for a set of conditions such as heat to reduce the number of organisms to one-tenth of the initial value, i.e.,... 

The term thermal stability (also thermostability) refers to the resistance of a protein to adverse intrinsic and extrinsic environmental influences, i.e., the thermal characteristic of the protein to remain steady against the dena-turation of its molecular integrity and inactivation of its biologic activity on facing high temperatures or other deleterious agents (6). One of the most important indices to measure protein stability is the decimal reduction time, or D-value, the time required to reduce 90% of the initial protein concentration exposed to the reference temperature. The D-value was used... 

Time t is defined as the decimal reduction time or D value. Therefore... 

Fig. 1 Microbial death rate curves that illustrate concept of decimal reduction (D values) and probability of survivors. (From Ref. l)...

The bacterial species to be used in a BI must be selected carefully, as it must be non-pathogenic and should possess above-average resistance to the particular sterilization process. Resistance is adjudged from the spore destruction curve obtained upon exposure to the sterilization process recommended BI spores and their decimal reduction times (D-values ... 

FIGURE 33.1 Dynamics of bacterial cell density (log x cfu/mL) at different periods (after 30, 60, 90, and 120 min) after incubation of microcapsules containing bacteria cells in alginate (AG) matrix (1%, 1.5%, and 2%) in simulated gastric juice (pH 2). The decimal reduction time values (D ) (min) are represented for each variant. 

The D value is the time required at a set temperature for a decimal reduction (i.e. one log or 90%) in the population numbers of a known organism. The size of the D value depends on the temperature, the microorganism and the other parameters in the beer that affect microbial grown (see Section 12.5.1 on hurdle technology). A higher temperature or lower pH will lead to a lower D value. A D value can be expressed in minutes or seconds. 

Figure 5.6. Alternative concepts for D> quantification of temperature effects (a) decimal reduction time, D o (see Equ. 5.8), and (b) Z value (see Equ. 5.9).

An additional alternative to the Arrhenius law for correlation of T dependencies is given by the concept of decimal reduction time, or the value, ... 

Decimal reduction time (DRT also called D-value) The length of time needed to kill 90% of the organisms in a given population at a specified temperature. 

As for pharmacokinetics and reaction kinetics, rate parameters can be defined for sterilisation processes, such as the first-order reaction rate constant (k) with the dimension reciprocal time and the half-life (ti/a). However, more commonly the term decimal reduction time or D-value is used. The D-value is the time required to inactivate 90 % of the present micro-organisms. 

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