AU701727B3 - Improved process for producing a feed pellet from grain - Google Patents

Description

The present invention relates to processes for producing a feed pellet from grain.

For convenience, the invention will be specifically described with respect to the preparation of fish meal from whole wheat grain, although it is to be understood that the invention is not to be limited thereto.

A single wheat grain essentially consists of bran layers surrounding an endosperm. The bran layers are rich in cellulose, hemicellulose, lignin, protein, minerals and vitamins, whereas the endosperm is rich in starch, but contains appreciable protein. An embryo is located in the bran layers and is 10 rich in protein and fat.

Wheat is traditionally dry milled by grinding through gravity fed drums that remove the external husk surrounding the wheat grain and produce bran and pollard fractions and flour fractions. The bran and pollard is usually used in a feed for poultry, and the flour, which contains starch 15 and protein, is used for making bread and other food products. The flour may be separated by washing and mixing to develop a protein rich dough, also known as gluten, which, as a cohesive wet lump, is removed from the starch slurry remaining.

Given the high nutritive value of wheat grain, it would be desirable to produce other forms of feed therefrom.

One such feed is that used in aquaculture. The conventional approach to producing feed in the aquaculture industry has been to harvest the ocean to produce a fish meal that is costly, may undesirably be diseased and consequently adversely affect the aquaculture, and is in increasingly short supply.

It would be advantageous for the aquaculture industry, therefore, to utilize the high nutritive value of wheat grain for producing a feed pellet for fish. Such a purely cereal based fish feed would overcome the problems inherent in ocean harvest based fish feed.

According to the present invention, there is provided a process for producing a feed pellet from grain comprising grinding the grain, separating the ground grain into a water insoluble protein rich fraction and a water suspendable starch rich fraction by introducing the ground grain into a liquid containing vessel that includes a bubbling gas stream for causing the protein rich fraction to float to the surface of the liquid in the vessel, ttwhereby the starch rich fraction remains suspended in the liquid, and leO* S 10 subjecting the water insoluble protein rich fraction to sufficient temperature and pressure to produce a pellet.

A particularly preferred wheat is Lawson wheat (or its derivatives) which is a red wheat that can be grown over large areas of cooler and higher altitude environments that receive a greater rainfall than would be suitable to standard Australian white wheat varieties. The Lawson red wheat yields about six times more protein per hectare than Australian standard white wheat but has a lower gluten strength that makes it an S"unacceptable wheat for making bread.

The low gluten strength of Lawson red wheat, however, is useful for purposes of the present invention.

Following is a description of a preferred process of the present invention for the purposes of more readily understanding and putting into practical effect the present invention.

A required amount of dry Lawson wheat grain is crushed and ground in a conventional grinding operation to form a fine particulate powder.

The powder is then introduced into a water containing vessel of a continuous separation device, through which vessel a bubbling stream of is 11/12/98 gas is passed for agitation of the components. The device serves to separate the powder into a floating fraction containing most of the protein and other insoluble components of the powder, such as cellulose, hemicellulose, lignin and fat, as well as a minimal amount of starch (hereafter referred to as the protein rich fraction) and a suspended fraction containing most of the starch (hereafter referred to as the starch rich fraction) from the powder.

The device is formed so that the powder enters at the top of the oo vessel and plunges downward into the water contained therein so as to 10 splash the water and create bubbles or a frothy mix in the vessel.

Such wet separation of wheat grain into the aforementioned two fractions has hitherto not been carried out, but is particularly energy efficient as it utilizes the differing flotation properties of components in the powder to separate out fractions not normally derived from wheat grain 15 milling.

The protein rich fraction may be used as the primary feed stock for formulating and processing animal feed pellets, such as fish feed pellets and poultry feed pellets.

The starch rich fraction may be used as the primary feed stock for fermentation processes that yield ethanol and a range of food sugars, amino acids and organic acids.

As an alternative to using dry Lawson wheat grain, a polished wheat (in which the bran is removed) may be used in the grinding and wet separation process to yield more pure protein and starch fractions.

The bubbling gas stream passing through the vessel comprises atmospheric air. The separation process may be optimised so as to result in a larger protein fraction being separated from the powder and a faster separation rate by adjustment of the pH of the liquid in the vessel to at or near the average isoelectric point of the different wheat proteins (pH 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 o" 10 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.

15 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.

11/12/98 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 10 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 S 15 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 minerals, 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.

a 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, minerals and fat is added to the fraction so as to supply the optimum level of energy and 8 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.

oo Various modifications may be made in details of design and construction without departing from the scope and ambit of the invention.

r THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A process for producing a feed pellet from grain comprising grinding the grain, separating the ground grain into a water insoluble protein rich fraction and a water suspendable starch rich fraction by introducing the ground grain into a liquid containing vessel that includes a bubbling gas stream for causing the protein rich fraction to float to the surface of the liquid in the vessel, whereby the starch rich fraction remains suspended in the liquid, and subjecting the water insoluble protein rich fraction to :o sufficient temperature and pressure to produce a pellet.

o 9 2. The process of claim 1 wherein the gas stream is an atmospheric air stream.

3. The process of claim 1 or claim 2 wherein the starch rich fraction is thereafter subject to fermentation, and that liquid effluent from the fermentation is recycled for use in the separation of the protein rich fraction 9*9999 9from the starch rich fraction.

Dated this 11th day of December, 1998 THE RESEARCH FOUNDATION INSTITUTE PTY LIMITED Patent Attorneys for the Applicant PETER MAXWELL ASSOCIATES 11/12/98