Grain moisture, high

In seeds, lipases may cause fat hydrolysis unless the enzymes are destroyed by heat. Palm oil produced by primitive methods in Africa used to consist of more than 10 percent of free fatty acids. Such spoilage problems are also encountered in grains and flour. The activity of lipase in wheat and other grains is highly dependent on water content. In wheat, for example, the activity of lipase is five times higher at 15.1 percent than at 8.8 percent moisture. The lipolytic activity of oats is higher than that of most other grains. 

Low-protein (12-16 %) complete feeds. They contain little grain and high amounts of bulky fibers. Since these feeds can accept only a small amount of moisture, addition of steam must be limited resulting in low moisture and temperature of the conditioned feed. Consequently, the manufacturing of high quality pellets is difficult. 

This effect is clearly shown by the data in Table 12-9, based on information presented by Derr (1938) for air dehydration with activated alumina at atmospheric pressure. The table presents temperatures within an uncooled bed of desiccant, 32 in. high and 12 in. in diameter, drying air that is at 75°F dry-bulb temperature, contains 9 grains moisture/cu ft, and flows at a rate of 5.2 cu ft/hr per pound of alumina. The break point was first detected after 7 hr of operation at which time the exit-air temperature was 213 F. However, 1 hr later (after 8 hr of operation), the water content of the outlet gas was still only 0,34 grains/cu ft, indicating a water-removal efficiency of 96%. 

A high grain moisture content and environmental temperature increase both fungi growth and activity of most enzymes. The hydrolysis of fats occurs at a faster rate than carbohydrates or proteins. Therefore, measurements of lipid damage via titrat-able acidity, pH, or free fatty acids are the most sensitive indexes to determine grain condition or soundness. These tests correlate with the evaluation of off-odors widely practiced by federal grain inspectors (Anonymous 1992) (Chapter 2). 

Foods high ia sucrose, proteia, or starch (qv) tend to biad water less firmly and must be dried to a low moisture content to obtain microbial StabiHty. For example, grain and wheat flour can support mold growth at moisture contents above 15% (wet basis) and thus are stored at moisture contents below 14%. Stored grains and oil seeds must be kept at a water activity below 0.65 because certain molds can release aflatoxias as they grow. Aflatoxins are potent carciaogens (see Food toxicants, naturally occurring). 

As energy costs have escalated in recent years, the use of high moisture food by-products in commercial animal feeds has also escalated, particularly in beef cattie and dairy rations, as a means of reducing production costs. Because of the broad activity spectmm, sorbates are extremely effective in the preservation of wet by-products, eg, brewers and distillers grains, beet pulp, citms pulp, and condensed whey (139). 

Adsorption for gas purification comes under the category of dynamic adsorption. Where a high separation efficiency is required, the adsorption would be stopped when the breakthrough point is reached. The relationship between adsorbate concentration in the gas stream and the solid may be determined experimentally and plotted in the form of isotherms. These are usually determined under static equilibrium conditions but dynamic adsorption conditions operating in gas purification bear little relationship to these results. Isotherms indicate the affinity of the adsorbent for the adsorbate but do not relate the contact time or the amount of adsorbent required to reduce the adsorbate from one concentration to another. Factors which influence the service time of an adsorbent bed include the grain size of the adsorbent depth of adsorbent bed gas velocity temperature of gas and adsorbent pressure of the gas stream concentration of the adsorbates concentration of other gas constituents which may be adsorbed at the same time moisture content of the gas and adsorbent concentration of substances which may polymerize or react with the adsorbent adsorptive capacity of the adsorbent for the adsorbate over the concentration range applicable over the filter or carbon bed efficiency of adsorbate removal required. 

Despite its advantages, SFE is employed routinely in only a few pesticide laboratories, for the extraction of low-moisture samples such as grains, pulses, dried fruit and tea. The technique requires specialized equipment because the extractions are performed at high pressure (45 psi) and elevated temperatures (around 60 °C) to maintain aC02 density ofO.85 gmL The analyte(s) may be trapped on Cig solid-phase material and eluted with a small volume (around 5 mL) of a polar solvent, such as acetonitrile. 

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