Preservative protection, influences

Macrodistribution. The ability of any wood preservative to control biodegradation is affected by the macrodistribution of the chemical within the wood product being protected. The macrodistribution of a preservative is influenced by three basic factors wood characteristics, treating process, and characteristics of the treating solution. Consideration of the principles of flow in wood and of the factors that influence the treatment of wood are covered in Chapters 3 and 4 14, 15). Suffice it to say that when the preservative has been distributed through the wood, fixation will occur either through chemical interaction between the preservative and the wood structure, between the preservative components themselves, or by physical deposition as a result of solvent loss. These fixation mechanisms are covered in the section on microdistribution. 

Unprotected steel corrodes at a rate which is generally assumed to be 0.1 to 0.2mm per annum. Factors that influence the actual rate of corrosion include the maintenance program applied by the owner - particularly preservation of protective coatings, efficiency of cathodic protection systems in ballast tanks, corrosive properties of the cargo carried and environmental factors such as temperature and humidity. Under extreme conditions it has been known for the annual rate of corrosion on unprotected steel exposed on both surfaces to approach 1mm. 

In the weakly acidic preservatives, activity resides primarily in the unionized molecules and they only have significant efficacy at pHs where ionization is low. Thus, benzoic and sorbic acids (pKa = 4.2 and 4.75, respectively) have limited preservative usefulness above pH 5, while the 4(p)-hydroxybenzoate esters with their non-ionizable ester group and poorly ionizable hydroxyl substituent (pKa ca. 8.5) have moderate protective effect even at neutral pH levels. The activity of quaternary ammonium preservatives and chlorhexidine probably resides with their cations and are effective in products of neutral pH. Formulation pH can also directly influence the sensitivity of microorganisms to preservatives (see Chapter 11). 

Modern methods of livestock production are intensive and the environmental conditions stress the animals. The use of antibiotics promotes growth and protects the animals from otherwise certain infection under these conditions. Antibiotic-like compounds formed in lactic acid fermentations prevent proliferation of spoilage and pathogenic microorganisms and increase the shelf life of the products. Nisin is a antimicrobial produced by a lactic acid bacterium and is used in some countries as a food preservative. Some lactic acid bacteria are capable of favorably influencing the fecal flora in man and animals. 

In the past, it has been well documented that the relative permeability of wood has a significant influence on the effectiveness of preservative treatments. Without adequate penetration, even the best preservatives will not provide sufficient protection and the wood will fail prematurely. Consequently, any developments in methods which increase the treatability of wood which are difficult to treat could have a significant impact on the wood preserving industry. 

Because the influence of drying parameters is not the same for all materials, optimal drying conditions vary depending on the final objective volatile retention, preservation of enzymatic activity and avoidance of protein denaturation, fat oxidation or crystallisation. Furthermore, some interactive influences may appear between components, an effect that is positive for protection of labile compounds by a network of polymers as polysaccharides, gums, proteins (Dumoulin and Bimbenet 1998). The phenomena may vary between centre and surface of drops, with some possible segregation by internal movement in the drop. 

Unit-dose and bi-dose systems are designed to deliver one or two doses into the nostril(s) (Fig. 9). As compared to multidose pump systems, unit-dose and bi-dose systems are distinguished by a different actuation principle. The dose volume is predetermined by the prefilled glass vial and sealed with a rubber stopper. The glass and rubber are the identical materials used in syringes. The benefit is an optimal protection against environmental influences. Unif-dose and bidose systems can be sterilized, and an aseptic filling procedure justifies the omission of preservatives. 

Several factors may influence the success or failure of a preservative to protect a formulation against microbial contamination. These factors include the interaction of the preservative with surfactants, active substances, other components of the vehicle, sorption by the polymeric packaging materials, and product storage temperature. Although hundreds of chemicals can fimction as germicides, only a few substances have made it to the marketplace. The small list is not based as much on a compound s effectiveness as an antimicrobial agent as on the compound s safety and effectiveness in the final product. 

Hexoses have found many biomedical applications, based mostly on their specific biological functions, but also on the unspecific (mostly protective) effects they have on tissues and organs. Considering the latter effects, hexoses have been found to exert a profound influence on the vitrification properties of ethylene glycol-based solutions used in cryobiology for the preservation of ooc)hes and other cells [95]. Glucose, mannose, and fructose have been shown to preserve physiological activities of various tissues, and have thus become important components... 

De la, R.P., Cordoba, G., Martin, A., Jordano, R., and Medina, L.M. 2005. Influence of a test preservative on sponge cakes under different storage conditions. Journal of Food Protection 68 2465-2469. 

This work, however, represents only a beginning. It is of considerable interest, for example, to examine how protectants interact with cell membranes in the absence of water, or in the presence of minute amounts of "residual" water. It is also important to consider how bilayers consisting of mixtures of phospholipids, which provide a better representation of actual cell membranes, respond to cryo and lyoprotectants. Along the same lines, it is important to consider how additional components of cell membranes, such as cholesterol, influence the behavior of anhydrous or nearly anhydrous bilayers. Our current research efforts are aimed at answering some of these questions, so that more effective methods of cell preservation can be devised. 

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