By carrying out the separation process at or near the average isoelectric point of the proteins in the wheat grain, the film forming property of the protein is enhanced with the result that the protein combined with the effect of the splashing of the powder on the surface of the liquid in the vessel contributes to the formation of large numbers of protein film encased bubbles of a very small diameter (say between 0.25 and 1.0 microns) that increase the available surface area for adsorption of other insoluble components of the powder.
The floating protein rich fraction, which has a protein concentration that is typically more than ten times higher than the protein concentration in the wheat grain, is then removed from the vessel by skimming from the liquid surface.
Any protein remaining in the suspended starch rich fraction may, if required, be subject to centrifugation or filtration, for instance, for isolation of this remaining protein. Alternatively, the residual protein in the suspended starch rich fraction may be allowed to pass to the fermentor.
The liquid in which the starch rich fraction is suspended passes to the fermentor via a flow regulating tap or similar controlled restriction at the bottom of the vessel that only allows enough of this liquid (or starch rich slurry) to pass therethrough so as to maintain the required liquid volume in the vessel for optimum separation of the fractions during the continuous operation of the flotation separation device. The pH of the starch rich slurry leaving the vessel may be adjusted to a desired range suitable for fermentation by addition of mild alkali.
The fermentor operating conditions will be adapted for greater efficiency so as to optimize the yield of ethanol and other fermentation products.
Furthermore, greater efficiency of the overall process may be achieved by recycling starch, not broken down by fermentation and which passes into the fermentor effluent, back to the flotation separation device, along with any protein and other unseparated insoluble components trapped in the suspended starch rich fraction in the flotation separation device Although water usage in the separation process is high, fermentor effluent liquid may be fed to the vessel for recycling a substantial volume of the water used in the process, thereby lowering overall water usage and minimising solid waste products produced or remaining from the process that are also carried in the effluent liquid.
It may be preferred to employ a preliminary vessel to dip the wheat grain in water so as to quickly remove any contaminating material therefrom by floating off the top of the water. The residence time of each wheat grain in the water in the preliminary vessel is relatively short so as to minimize absorption of water by the grain. The grain may also be gently agitated whilst dipped in the water of the preliminary vessel so that heavier contaminating particles, such as stones and the like, may settle at the bottom of the vessel and be removed by traps. Additives may be supplied to the water in the preliminary vessel to control microbiological growth or pH and surface chemistry properties.
The wheat grain is then ground into a meal for separation by the flotation separation device.
Also, it may be preferred to employ a starch settlement vessel or tank that receives a controlled amount of the starch slurry released from the bottom of the separation vessel. Starch settling at the bottom of this tank may be fed to the fermentor or for other bioprocessing.
In producing the feed pellets from the protein rich fraction skimmed from the surface of the liquid in the separation vessel, the choice of a wheat grain having a weak gluten strength is an important consideration.
The properties required in a pellet suitable for an animal feed are that it has a high level of protein of suitable mixture of amino acids and a range of other ingredients that give the final pellet the desired level of energy and a range of vitamins and mineras, which vary between animal species. It is also required to remain in a cohesive form, but have the desired level of digestibility when consumed. This is of particular importance when used in water for fish feed in that the pellet should not fragment in the water but can be easily bitten off in small segments and readily digested by the fish species.
Wheat protein (ie gluten) has not been used extensively in feed pellets due to its high gelatinising properties which result in an amorphous mass when subjected to heat and pressure in forming a feed pellet. This can be overcome by the use of wheats such as Lawson and its derivatives which have weak gluten strength or by the addition of other ingredients, such as bran, which weaken the agglutinating forces of the gluten and/or by the controlled use of heat, water and pH to partially degrade the gluten structure.
Once the gluten strength of the protein rich fraction has been assayed and, if required, adjusted so that it falls in the desired range for pelletization, a suitable amount of amino acids, vitamins, mineras and fat is added to the fraction so as to supply the optimum level of energy and micronutrients required for the target animal species to which the pellets will be fed.
Pelletization then occurs by passing the nutrient reinforced protein rich fraction through an extruder or die that, by application of suitable pressure and temperature, creates a weakly cohesive pellet of a desired shape and texture or hardness that is digestible for the target animal species.
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