GB2220124A - Spent grain-based animal feed material and method for its production - Google Patents

Abstract

A process for the preparation of animal feed material comprises the treatment of spent grains containing water- insoluble carbohydrate with one or more carbohydrate lyase enzymes to increase the content of available carbohydrate therein, said grains containing or being subsequently contacted with lactic acid producing microorganisms. An animal feed material may comprise spent grains having an overall dry-matter content of 23-30% by weight and containing at least one carbohydrate lyase enzyme.

Description

"NOVEL GRAIN-BASED ANIMAL PEED MATERIAL AND A METHOD FOR ITS PRODUCTION" The present invention relates to a novel grain based animal feed material and a method for its production.

In brewing and in related processes such as distilling and vinegar brewing and production of malt extract and barley syrups, crushed malt and other cereals are treated with water to extract carbohydrate for fermentation. The grain may be that of any cereal, but will primarily be barley or wheat which has been subiected to a malting process, either by natural germination to produce the appropriate enzymes, or by addition of enzymes including malt enzymes. It is normal practice in all of these industries to allow the crushed grain to saccharify under optimal conditions of temperature and pH. Most then inactivate the enzymes by raising the temperature.

The wet residue known as "spent grains1' consists primarily of the protein and fibre from the original material, but due to modern products and production plant there is also a carbohydrate content, in various forms, ranging widely from 0% to sometimes about 40% of the spent grains dry matter. Such spent grains normally contain about 18-25 & by weight of dry matter.

Spent grains are commonly used as a feedstuff for ruminant animals, in view of their high protein content and the ability of ruminants to digest fibre. However, demand for such feed material is commonly seasonal, particularly in countries such as the United Kingdom where cattle are out to grass in the summer and it is normally necessary, therefore, to store the grains in an acceptable state for feeding during the winter. Consistency of the material is important to the farmer and excessive residual starch can be dangerous as a substrate for spoilage organisms.

In general, storage stability is achieved either by ensiling the grains in bulk in the wet state in which they come out of the brewery or by drying. In the drying process, the spent grains are normally de-watered by mechanical means such as screw presses or centrifuges but this procedure is capable of increasing the dry matter content to no more than about 35% by weight and in order to remove sufficient water to stabilise the spent grains, a great deal of energy is required. This is expensive and generally undesirable and ensilage is generally preferred in countries where there are enough animals to consume them within economical delivery distance.

The bulk ensilage of the wet spent grains can be achieved satisfactorily in such moist conditions only if procedures are adopted to reduce the pH to 4.0 or below as quickly as possible, primarily by promoting the growth of bacteria producing lactic acid, thereby inhibiting the growth of infecting organisms. However, it is essential to the growth of such bacteria that there should be sufficient nutrients, in particular carbohydrates, present in the spent grain material. Since the objective of most grain processes is to extract as much carbohydrate as possible from the grain and current technology enables that to be done without detriment to their main product, there is a risk of there being insufficient available carbohydrate to sustain the growth of the required lactic acid producing bacteria.

However, the grains normally contain significant amounts of carbohydrate material which is not directlv usable by the bacteria, for example undeqraded starch, glucans and cellulose. We have found that by including appropriate enzymes with the spent grains, sufficient available carbohydrate can be qenerated to promote growth of lactic acid bacteria.

When the dry matter of the spent grains is below about 23% they are more difficult to transport and handle as well as having a lower nutritional value in relation to their gross weight and mav give rise to effluent problems on the farm. further more, the free liquid associated with the grains consists mostly of incompletely removed carbohydrate extract. Consequently, it is desirable to remove as much free liquid as possible from the spent grains prior to ensilage.

On the other hand, mechanical de-watering of the spent grains is generally used to increase the dry matter content to above 30% and while this may be beneficial in recovering further liquid for re-cycling to the brewing process and reduces transport costs by reducing the amount of liquid to be transported with the grain, the resulting material commonly does not ensile well because excessive de-watering tends to spoil the necessary anaerobic conditions and also, as indicated above, remove the free carbohydrate necessary for the growth of lactic acid producing bacteria.

The former difficulty can be overcome by adding water. In general, therefore, the dry matter content of the spent grains for ensilage will desirably be between 23% and 30% by weight.

The latter difficulty can be overcome by adding a suitable nutrient for the lactic organisms, but these are either expensive or in some cases impracticable to recover from other process waste materials.

According to the present invention we provide a process for the preparation of animal feed material in which spent grains containing water-insoluble carbohydrate are treated with one or more carbohydrate lyase enzymes to increase the content of available carbohydrate therein said qrains containing or being subsequently contacted with lactic acid producing microorganisms.

In general, the type of enzyme used will depend on the nature of the spent grains. Where there is adequate starch remaining in the grains, a fungal or other amylase enzyme may conveniently be used. Residual enzyme of the main process, if it has not been too much inactivated by the process, may be utilised in some cases by mixing with batches known to contain insufficient enzyme.

Where, however, there is insufficient starch remaining, it will be necessary to degrade, for example, cellulose, in the grains, e.g. using an appropriate cellulase or hemicellulase. A combination of enzymes can be used to maximise the recovery of soluble carbohydrate from all or any of the sources available.

The following Table shows a range of enzymes available from one supplier. Optimal activities of course depend both on temperature and pH, so specific rates and combinations have to be designed for each individual case. All these enzymes produce end products which are fermentable by both yeast and lactic bacteria.

TABLE At 1600F and Commercial Enzymes Optimal Optimal ( ) pH Approx % Description Included pH Temperature of max activity OF 0F Biotempase a-amylase 4.8-7.5 155-175 95 (6.0) Biomaltase B-amylase 4.5-6.5 100-130 s (4.7) Bioglucanase L57 B-glucanase 4.0-6.0 120-140 90 (5.0) Fungal Protease Protease 6.0-11.0 120-140 10 (4.7) Biase a-amylase ss-glucanase 5.5-6.0 * * Biocellulase A Cellulase Hemicellulase B-glucanase 3.5-4.5 130-145 70 (4.6) Biocellulase T Cellulase Hemicellulase Protopectinase 3.0-6.0 115-135 20 (4.6) Bioglucanase S Glucanase 3.5-6.5 140-160 100 (*) Xylanase 4.5-6.5 100-120 25 (4.5) Bioxylanase Xylanase Cellulase Hemicellulase B-glucanase 4.0-6.0 115-140 25 (4.5) *depending on proportions in mixture.

In any case, the enzyme(s) should be added in such a quantity that the available carbohydrate increases to at least 4% of the dry matter unless some acidification has already occurred in which case some of the available carbohydrate will have already been consumed. Where there is water-soluble carbohydrate already present or the pH is lower, clearly less water-insoluble carbohydrate will need to be converted for the purpose of ensilage, so more will be available for recycling in the process.

We have found that this quantity of water soluble carbohydrate generally permits the lactic acid bacteria, which are almost universally present in the spent grains handling plant of breweries and other similar installations e.g. at 107 organisms per gm. in wet grains, to reduce the pH to below about 4.2 sufficiently rapidly to avoid contamination by other microorganisms.

The process according to the invention mav be effected in a number of ways. Since the added enzymes will produce essentially the same watersoluble carbohydrate as the original process, namely sugars, the addition of further enzyme can often be used to produce sufficient water-soluble carbohydrate for de-watering to produce more extract to be recycled for beer or other production while leaving an adequate amount, that is more than 4% based on dry matter, in the spent grains.

In fact, the normal procedure resulting in production of spent grains involves the filtration of the mash of malted grains in an extraction vessel, e.g., a lautertun, where the grain itself acts as the filtration medium, the extract being drainedoff for further processing, while the spent grains, at 18-23% dry matter, can profitably be subjected to de-watering, which however is less effective if the starch is less completely degraded to sugars, The additional extract produced by de-watering is normally re-cycled, commonly by admixture with a subsequent batch of extract. Thus, enzyme treatment according to the invention enhances the utilisation of raw materials if added before the dewatering stage of the process in such conditions.

Dewatering is advantageously effected on a centrifuge, e.g. a decanter centrifuge such as a Sharples P3400 centrifuge. In such a procedure, the spent grains may be conveyed from the extraction vessel on a screw conveyor or otherwise to a dump tank. Enzyme may be added at this stage, where its activity will depend, inter alia, on the residence time. The grains may be fed from the dump tank, to a decanter centrifuge, the recovered extract being passed to a holding tank for storage and recyclinq, while the de-watered grains, usuallv with the addition of aqueous liquid and with or without subsequent addition of other process waste materials consumable hy animals such as spoilt beer, yeast etc. may be collected in vessels from which they are later drawn for delivery to farms for immediate consumption or for ensilage; alternatively they may be bagged for ensilage.

Transfer from dump tank to centrifuge usually begins as soon as grains arrive at the dump tank and is normally complete in 1 to 3 hours. There can thus be little enzyme activity in the first grains of a batch reaching the centrifuge; activity will continue in the dewatered grains, particularly before the pH is reduced by the lactic organisms.

Thus sufficient additional water-soluble carbohydrate can be produced to provide both the required amount of water-soluble carbohydrate remaining in the de-watered spent grains and a useful enhancement of the water-soluble carbohydrate in the re-cycled extract.

The enzyme may be added, conveniently in solution, to the grain while still in the extraction vessel. The grain is normally subjected to at least one washing or sparging step in the extraction vessel and this can readily be followed by application of the enzyme solution after the termination of normal extraction and before or during discharge of the spent grains. A significant degree of control can thus be exercised by varying the length of time between addition of enzyme and centrifugation to ensure that at least 4% of the spent grains dry matter can be converted and that risk of spoilage of the spent grains is decreased e.q. by reducing the residual starch content of the grains to less than 10% where necessary.Alternatively, the enzyme can be added to the spent grains whether dewatered or not in a storage facility or on a conveyor while being transported to such a facility.

In some cases, a brewery will not attempt to recover additional extract by de-waterina the spent grains but will simply extract as much as possible by very slow filtration in the extraction vessel. In this case, the enzymes will be applied to the spent rains after such filtration and the treated grains simply passed on for silage, either in bulk or after bagging.

One case in which the enzymic treatment according to the invention can produce particularly large benefits is where the spent grains have been used for the production of low alcohol beer. In that case, the saccharification procedure is checked at a particularly early stage and the natural enzymes inactivated. As a consequence, the spent grain contains a very significant amount of starch and enzymic treatment according to the invention can thus liberate a relatively large amount of valuable extract for re-cycling, while still leaving adequate water-soluble carbohydrate in the spent grains (4% or greater) and reducing the risk of spoilage The enzymic treatment according to the invention will normally take place at or close to the optimal temperature for the enzyme at the pH concerned, which will normally be about pH 5.0-6.0.A brewery mash will normally be filtered at about 1600F but can readily be allowed to cool slightly to approach such optimum temperatures. Thus, the optimum temperature for malt amylase is about 1200F. The enzyme treatment will optimally be complete in less than 2 hours.

It may be advantageous in some cases to add one enzyme preparation before dewatering, during which the temperature usually falls by about 200F, and another afterwards. For instance brewery extract could be maximised by use of amylase/glucanase before dewatering, with subsequent addition of the more temperature-sensitive xylanase/hemicellulase/ glucanase mixture to provide substrate for the lactic organisms. Once in the silo, temperature falls comparatively slowly; typically, the silo temperature would be in the ranqe of 140 to 1000F for several hours.

The spent grains leaving the extraction vessel may have as little as 10t dry matter, in which case the material has the consistency of thin porridge, or as much as 18-23% dry matter, in which case the material is iust pumpable. It is normally preferred to reach about 18-23% dry matter in the filtration step, in order to maximise the amount of extract removed and minimise effluent. It is found that the enzymolysis according to the invention assists in improving the handling of the relatively dry (18-23% dry matter) grains, by liberating water bound by the starch prior to degradation. Thus, if the spent grains in the extraction vessel are allowed to reach a relatively high dry matter content and are then treated with enzyme, water will be liberated and will improve the pumpability of the grains. It is thus clearly preferable in such cases to add the enzyme before removal of the spent grains from the extraction vessel rather than subsequently. The handling characteristics of the spent grains on the farm will also be improved as they will be less fluid.

In general, it is preferred that the concentration of water-soluble carbohydrate in the ensiled spent grains should not be above 6t by weight of the dry matter. This reduces risk of spoilage and generation of excessive amounts of lactic acid although, in fact, the low pH eventually inactivates the enzyme.

According to a further feature of the invention we provide an animal feed material comprisinq sDent grains having an overall dry-matter content of 23-30% by weight and containing at least one carbohydrate lyase enzyme.

Such a feed composition will normally contain, at about pH 5.5 as indicated above, at least 48 of water-soluble carbohydrate based on the weight of dry matter.

Where the feed composition has had sufficient time to generate lactic acid, the pH will reduce to about 3.5. At that pH, the enzyme will normally be in an inactive form.

United Kingdom patent 2078083 describes animal feed material comprising spent grains having an overall dry matter content of 23-30% by weight and containing added nutrient material, such as spoilt beer, malt dust, trub, yeast, acid whey etc. Such additions increase the amount of nutritional feed for animals, either by adding metabolisable energy, e.g. as with malt dust and/or spoilt beer, or digestible protein, as with yeast, trub and acid whey. Of those mentioned, only the spoilt beer and whey would be a satisfactory substrate for lactic organisms. When added in liquid form, as in the case of spoilt beer, such materials provide the possibility of adjusting the dry matter content of the spent grains from an excessively high level, over 30% to within the desired range of 23-30%.

Such additions can provide additional animal nutritional matter in the present case also, although all the supplementary water-soluble carbohydrate for lactic acid fermentation will be provided primarily by enzymolysis according to the invention, so ensuring stability of the silage without other additions.

It should be noted that where spent grains are not de-watered, because the amount of usable soluble carbohydrate is deemed inadeauate, use of enzymes in accordance with the invention, by increasing the amount of fermentable carbohydrate to a usable level, may make re-cycling economical.

Since the extract would otherwise have been discarded as effluent either at the factory, in transit or on the farm, treatment according to the invention combined with re-cycling can provide considerable savings in effluent treatment and also benefits the environment.

The following Example is given by way of illustration only: Example Spent grains obtained from a brewery and untreated by enzyme addition or centrifugation were ensiled for six days in an experimental silo of a tvpe known to replicate performance in bulk, on farms.

During that time the pH rose from 4.2 to 4.6, showing that spoilage was occurring. On contact with lactic acid bacteria, the pH of the spent grains so produced would normally fall, if there was sufficient carbohydrate, to about 4 in 1-2 hours and continue to fall to about 3.5. On analysis the dry matter content was found to be 21.8% by weight, the starch content 22.3% by weight and the water-soluble carbohydrate content 2.2% by weight. They were dewatered in a centrifuge and then were treated with a commercial amylase at an arbitrary rate of 800 ml per 1000 kg for 1 hour both at ambient temperature and at about 1300. The resulting treated de-watered spent grains had a dry matter content of 30.1% by weight, starch content of 9.9 by weight and a water-soluble carbohydrate content of 13.7% by weight which would have been more than adequate for the lactic acid bacteria. The extract removed from the spent grains before enzyme treatment was equivalent to a saving of about 1.5% of the raw materials. The additional soluble carbohydrate made available by the enzyme treatment was sufficient to increase the residual soluble carbohydrate in the spent grains to the necessary 4% and also provide about 2% further saving of raw materials.

Claims (15)

CLAIMS:

1. A process for the preparation of animal feed material which comprises the treatment of spent grains containing water-insoluble carbohydrate with one or more carbohydrate lyase enzymes to increase the content of available carbohydrate therein, said grains containing or being subsequently contacted with lactic acid producing microorganisms.

2. A process as claimed in claim 1 wherein said carbohydrate lyase enzyme comprises a fungal or other amylase enzyme.

3. A process as claimed in claim 1 or claim 2 wherein said carbohydrate lyase enzyme comprises glucanase.

4. A process as claimed in claim 1 wherein the carbohydrate lyase enzyme comprises a cellulase or hemicellulase.

5. A process as claimed in claim 1 wherein said enzymic treatment increases the available carbohydrate to at least 4% of the dry matter in said feed material.

6. A process as claimed in claim 1 wherein the pH of the spent grains is rapidly dropped to below about 4.2 by lactic acid producing bacteria.

7. A process as claimed in claim 1, wherein said enzyme is added to the spent grains in a dump tank, or in transit thereto, prior to a dewatering process.

8. A process as claimed in claim 1 wherein said enzyme is added to the grains in a wort extraction vessel prior to or during discharge.

9. A process as claimed in claim 1 wherein the carbohydrate lyase enzyme preparation is added to the grains, with or without other additions, in a silo or holding vessel or in transit thereto from the wort extraction vessel, whether the grains have been dewatered or not.

10. A process as claimed in claim 9 wherein said enzymic treatment takes place at a pH of about 4.0 - 6.0.

11. A process as claimed in claim 1 wherein the concentration of starch in the ensiled spent grains is no greater than 10% by weight of the dry mater.

12. A process as claimed in claim 1 substantially as herein described.

13. A process for the preparation of an animal feedstuff substantially as herein defined in the Example.

14. An animal feed material comprising spent grains having an overall dry-matter content of 23-30% by weight and comprising at least one carbohydrate lyase enzyme.

15. An animal feed material as claimed in claim 12 comprising at least 4% of water-soluble carbohydrate based on the weight of dry-matter when at an initial pH of about 5.5 and proportionally lower at lower pH's.