Water activity powder

Povidone—iodine is a brown, water-soluble powder containing approximately 10% iodine. However, the amount of free iodine, which is responsible for the antimicrobial activity, is low in a concentrated solution, but is released as the solution is diluted (41). Concentrated solutions have actually been contaminated with bacteria (42). For use as an antiseptic, povidine—iodine is diluted with water or alcohol to a concentration of 1% iodine. Detergents are added if it is used as a surgical scmb. lodophors are important as broad-spectmm antiseptics for the skin, although they do not have the persistent action of some other antiseptics. They are also used as disinfectants for clinical thermometers that have been used by tuberculous patients, for surface disinfection of tables, etc, and for clean equipment in hospitals, food plants, and dairies, much as chlorine disinfectants are used. 

LIG. 37 Stability map for dairy powders containing amorphous lactose. The critical water activity (0.37 aw) corresponds to the water activity of amorphous lactose with Tg of 24 °C (and a moisture content of 6.8 g water/100 g solids) [reproduced with permission from Roos (2003)]. 

Roos, Y.H. 2002. Importance of glass transition and water activity to spray drying and stability of dairy powders. Lait 82, 475-484. 

Activated carbon may be used as a powder, in which form it is mixed in with the liquid to be treated, and then removed by filtration. It may also be used in granular form. When the use of carbon is low, it is normally economic to regenerate it, and this is usually the case with powder. Granular carbon is normally regenerated after use. Because it has a low affinity for water, activated carbon may preferentially adsorb components from aqueous solution or from moist gases. 

With continuous development of systems for controlled drug release, new materials are being used whose influence on peptide stability must be carefully examined. Thus, the model hexapeptide Val-Tyr-Pro-Asn-Gly-Ala (Fig. 6.30) embedded in poly (vinyl alcohol) and poly(vinyl pyrrolidone) matrices had rates of deamidation that increased with increasing water content or water activity, and, hence, with decreasing glass transition temperature (Tg). However, the degradation behavior in the two polymers differed so that chemical reactivity could not be predicted from water content, water activity, or T% alone. Furthermore, the hexapeptide was less stable in such hydrated polymeric matrices than in aqueous buffer or lyophilized polymer-free powders [132],... 

The inclusion of the a routine microbial limit test in a marketed product stability protocol depends on the pharmaceutical dosage form. Typically, the test would be used only for nonsterile products, especially oral liquids, nasal sprays, and topical liquids, lotions, and creams that have sufficient water activity to support the growth of microorganisms. In contrast, tablets, powder- and liquid-filled capsules, topical ointments, vaginal and rectal suppositories, nonaqueous liquids and inhalation aerosols with a water activity too low to allow for the product to support the growth of microorganisms would not be routinely tested. 

Effect of Water Activity. A preliminary study was done to determine the a at which encapsulated orange peel oil was the most stable to oxidation. Figure 1 summarizes the results of this study. The formation of the limonene oxidation product, limonene oxide, was the slowest for the powder adjusted over Mg(NO3)2 (a 0.536). While the levels of oxidation product do not follow in exact order of a, it is evident that better storage stability correlates with a higher a of the powder. This relationship was not anticipated. Literature on lipid oxidation (2, 2) indicates that there is an optimum a for product... 

Sample powders were dried in a vacuum oven at 60 C for 7 hours and cooled to minimize the hysteresis effect prior to storage in the dessicators of various water activities. In addition to Drierite, five saturated salt solutions were used in dessicators. These salt solutions were lithium chloride, magnesium chloride, potassium carbonate, sodium nitrite and potassium chloride. Their water activities were 0.110, 0.330, 0.440, 0.650 and 0.850, respectively, at 20 C. Each sample contained 1.2 to 1.5 g powder and four-week equilibration time was employed. The percentage of... 

The type (e.g., liquid, solid, powder, gel, syrup, emulsion, granule) and range of food samples (raw ingredients to final products) for water activity measurement are immense. The amount of sample required for measurement is typically 5 to 10 ml. A homogeneous and representative sample should be prepared and placed into the sample cup. For the majority of samples, no preparation is necessary the sample is simply placed into the cup. Multicomponent (e.g., muffin with raisins or pizza) and coated samples (e.g., breaded foods or chocolate-covered bar) may have to be sliced, crushed, or ground in order to obtain a representative sample. If sample preparation is necessary, then a consistent technique must be used with each sample to ensure reproducible results. 

H Stapelfeldt, BR Nielsen, LH Skibsted. Effect of heat treatment, water activity and storage temperature on the oxidative stability of whole milk powder. Int Dairy J 7 331-339, 1997. 

For this reaction the amine (Aldrich Chemical Company, Inc.) from a freshly opened bottle is dried by distillation from active powdered calcium hydride. Addition over 1 min or less is required to avoid excessive foaming which has been observed when slow or dropwlse addition is used. Older samples of amine which contain water should be pre-dried overnight with potassium hydroxide. 

When the whey powders are stored at (water activity)... 

Hu. J.-Y., Aizawa, T., Magara, Y. (1997) Evaluation of adsorbability of pesticides in water on powdered activated carbon using octanol-water partition coefficient. Wat. Sci. Tech. 35, 219-226. 

Figure 13.2 The influence of heat treatment on the shelf life of freeze-dried tomato powder stored at 23 °C and different water activities (Xext> 420 = 0.9 corresponds to the limit of acceptability)., A, preheated at 40 °C and aw = 0.11 (about 30% of glutamic acid has reacted to fructosylglutamic acid) O, A, unheated. Reproduced from Eichner and Ciner-Doruk577 with permission from Elsevier.

Influence of Moisture Content and Water Activity on the Oxidation of Fat in Milk Powder... 

The maximum shelf-life of bulk packaged WMP containing 3% moisture is about 6 months at 30°C (Kjaergaard Jensen, 1988). The oxidation of WMP, as measured by peroxide value, is dependent on the moisture content of the powder, van Mil and Jans (1991) reported that under similar storage conditions, the peroxide value of WMP increases more rapidly for powder containing 3% moisture than in powder containing 2.4% moisture. The water activity (aw) range for WMP is usually 0.13 0.20, with a typical value from 0.16 to 0.18 (Wewala, 1990). Stapelfeldt et al. (1997) found that the quality of WMP is maintained best at aw between 0.11 and 0.23, whereas the quality of the powder decreases when stored at aw of 0.31 at 45°C. However, the critical aw for improved oxidative stability of WMP stored at 40°C for one year is 0.21 0.24 at a moisture level of 3.4% (Wewala, 1990). 

Wewala, A.R. 1990. Manipulation of water activity An important aspect of extending the shelf life for whole milk powder. Report, pp. 13-16, N.Z. Dairy Research Institute, Palmerston North. 

An important case is the application of enzymes in laundry detergents. Market trends in the United States show that consumers prefer liquids to powder detergents by a ratio of 2 to 1. These products are stored with no temperature control on shelves in the presence of harsh surfactants, such as linear alkylbenzyl sulfonate (LAS) and require extraordinary measures for stabilization. LAS, by its nature as an effective cleaning agent, causes surfactant-induced unfolding in proteins. There are countless examples of the development of stabilization systems in the intellectual property space. A common theme is to reduce the water activity and to use borate/glycol stabilizers that bind to the active site of proteases. 

Pancreatin Obtained from porcine or bovine (ox) pancreatic tissue. Produced as a white to tan, water-soluble powder. Major active principles (1) a-amylase, (2) protease, and (3) lipase. Typical applications used in the preparation of precooked cereals, infant foods, and protein hydrolysates. 

Pepsin Obtained from the glandular layer of hog stomach. Produced as a white to light tan, water-soluble powder amber paste or clear, amber to brown, aqueous liquids. Major active principle pepsin. Typical applications used in the preparation of fishmeal and other protein hydrolysates and in the clotting of milk in manufacture of cheese (in combination with rennet). 

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