Sodium hydroxide treatment straw

For example, when cell walls of maize stem were treated with sodium hydroxide (0.1M) at 20°C for various times to release different amounts of phenolics, a highly significant correlation (r = 0.98) was found between the amount of phenolics released and wall biodegradability (measured by cellulase ) (5). It is of interest to note that alkali treatment of poor quality graminaceous forages (e.g., cereal straw) is used commercially to increase their biodegradability, and thus their feed value for the animal (1). 

An alternative alkali to sodium hydroxide is ammonia, which may be applied to straw in the anhydrous form or as a concentrated solution. As both forms are volatile, the process has to be carried out in a sealed container, which may be formed by wrapping a stack of straw bales in plastic sheeting. As ammonia is a weaker alkali than sodium hydroxide, it reacts slowly with the straw the time required for treatment ranges from 1 day, if heat is applied to raise the temperature to 85 °C, to 1 month at winter temperatures. The ammonia is added at 30-35 kg/t of straw, and when the stack is exposed to the air about two-thirds of this is lost by volatihsation.The remainder is bound to the straw and raises its crude protein content... 

Straw normally carries bacteria that secrete the necessary urease it is important that the straw should be wet enough (about 300 g water per kilogram) to allow the hydrolysis to take place. After the application of urea, the straw is sealed in the same way as for treatment with ammonia. Urea ammoniation of straw has proved reasonably effective in improving its nutritive value but is not as consistently effective as ammonia or sodium hydroxide. 

The digestibility and intake of straws may be improved by treatment with sodium hydroxide or ammonia (as a gas or derived from urea). Such treatment is expensive, and the more appropriate way of making the best use of straws is to supplement them, especially with a source of rumen-degradable protein. 

The twin-screw extruder has proved to be a versatile tool for continuous treatment of vegetable matter, either for food or non-food applications. Trials for the direct alkaline extraction of xylans from wheat bran in a twin-screw extruder were unsuccessful. Bran impregnation with sodium hydroxide in the twin-screw extruder was very efficient, but it was necessaiy to make the separation between the hemicellulosic gel and the lignocellulosic matrix in another apparatus and remained difficult without a dilution to a L/S ratio of 50. Bran and straw co-extrusion was therefore investigated to be able to reduce the L/S ratio. Straw fibres form a dynamic plug in the restrictive elements of the screw profile just after the filtration zone. The pressure induced in the extruder sheath by the cellulosic fibres enabled the liquid/solid separation. 

Forages such as the cereal straws, in which the cellulose is mixed or bound with a high proportion of lignin, may be treated chemically to separate the two components. The treatment processes and their effects are described in detail in Chapter 20. The chemicals used are mainly alkalis (sodium and ammonium hydroxides), and they improve the dry matter digestibility of cereal straws quite dramatically, from 0.4 to 0.5-0.7. 

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