GB1584539A - Flavour enhancement of dry food compositions - Google Patents

Abstract

A composition for dog food is described which is more acceptable by virtue of its improved taste, of the dry or intermediate moisture type, containing as taste enhancing agent, L-lysine, D-lysine, a mixture of D- and L-lysine, their respective salts or a mixture of such salts and of acids.

Description

(54) FLAVOUR ENHANCEMENT OF DRY FOOD COMPOSITIONS (71) We, RALSTON PURINA COMPANY, of 835 South Eighth Street, St. Louis, Missouri 63188, United States of America, a Body Corporate organized and existing under the laws of the State of Missouri, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a dry food composition, particularly valuable as an animal and especially dog food, which has improved palatability by virtue of its inclusion of the amino acid, lysine, or salts thereof.

Commercial development of petfoods, particularly dog foods, has grown considerably in recent years. It is, however, difficult to provide a commercial petfood which meets all of three, frequently conflicting, criteria: (1) attractiveness to the pet owner; (2) attractiveness and palatability to the pet; and (3) proper nutritional balance.

This applies particularly to dogs, who have extremely keen and finicky senses of taste and smell, far more sensitive than those of humans or most other animals, Commercial petfoods can be divided into three broad, although sometimes somewhat dverlapping, classes, which can generally be characterized by their moisture contents. The first of these classes is that of dry petfooods. Dry petfoods generally contain less than 20%by weight moisture and more commonly less than 15%; indeed, the moisture content may be as low as 10% by weight or even less. The second class of petfood is commonly called the "canned" food and has a relatively high moisture content, typically above 55% by weight.

The third class of petfood falls between the first two and, for obvious reasons, is generally termed the "intermediate moisture" petfoods - they will normally contain at least 12% by weight moisture and more commonly from 15 to 55% by weight moisture. Each of these different classes of petfood has its own advantages and disadvantages.

Dried petfoods are generally expanded or puffed products now mostly produced by extrusion techniques. The extrusion cooking processes for the production of dry petfoods have been a significant factor in the growth of this segment of the market because of the better cooking achieved, better mixing of ingredients and the desirable texture produced by puffing or expansion processes. Because of the low moisture content of dry petfoods, a high degree of nutritiónal balancing of the ingredients is possible, thus providing excellent nutrition for the animal. Indeed, from the point of view of nutrition, the dry petfoods are probably the best of the three classes. Moreover, they are very storage-stable because of their low moisture content. They do not require refrigeration or special packaging techniques and can be kept for a considerable time without refrigeration even once the packet has been opened. Furthermore, they are very convenient for the pet owner to use. However, despite their advantages they have one significant disadvantage: although they are generally well accepted by the animal, they have a significantly lower palatability than the other classes of petfood. Thus, despite the advantages of this class of petfood, there is a need for additives or ingredients which can be included to improve their palatability.

Canned petfoods have a high moisture content and typically contain real meat. They normally have a very high palatability and are generally extremely well accepted by all animals. They are, moreover, extremely attractive to the pet owner. However, canning is an expensive process which adds to product costs in a very competitive industry. Moreover, once the can has been opened, canned petfoods have very limited storage stability and can only be kept for a very short time, even under refrigeration. This limited stability is due primarily to the very high moisture content of canned foods which provides an excellent medium for the growth of bacteria and mould.

An obvious solution to the problems posed by the limited palatability of dry petfoods and the limited storage stability of canned petfoods is to increase the moisture content of the food to a level at which it is readily acceptable to the animal but below the level at which canning or sterilization is required for maximum bacteriological stability. This is achieved in intermediate moisture petfoods, which are provided with bacteriological and mycotic stability by controlling the water activity. Water activity is controlled by using sugar solutions and other water-soluble solids, for example, as disclosed in U.S. Patent Specifications No. 3,202,514, No. 3,482,985, No. 3,516,838, No. 3,615,652 and No. 3,653,908. In addition to the sugar or other water-soluble solids used to control water activity, additional bacteriological and mycotic stability is provided by the incorporation of more conventional bacteriocides or anti-mycotics which "kill" or control the bacterial and mycotic populations. However, although these types of product are more acceptable to animals than are dried petfoods, they still do not have the palatability of high moisture or canned foods and, indeed, the very additives needed to provide storage stability generally depress palatability below what it would be without those additives. Furthermore, in intermediate moisture products, like dry products, ingredient formulation becomes exceptionally critical and considerable care has to be taken in altering ingredients, even replacing one ingredient by another generally reckoned to be equivalent, in case the alteration depresses palatability. Formulation of these types of product, therefore, becomes extremely complex since each ingredient used must be evaluated not only for its texture and nutritive properties but also for its relative effect on palatability. This, of course, reduces the flexibility in formulation that a pet food manufacturer would like to have. Thus, the introduction of intermediate moisture petfoods has not obviated the need for improving the palatability of dry petfoods.

We have now surprisingly discovered that lysine, either in its 1 or its d form, and salts thereof will improve the palatability of dry petfoods, particularly for dogs.

Thus, the present invention consists in a dry food composition having added thereto, in an amount sufficient to enhance palatability, lysine or a salt thereof.

Lysine exists in two optically isomeric forms, d-lysine and l-lysine and details of the properties and preparation of the different forms of lysine appear in Entry No. 5455 in the 9th Edition of The Merck Index, published by Merck Sharp and Dohme Limited, 1976.

Either the individual d- and 1- isomers or a d,l-lysine mixture may be used. Lysine, lysine mixtures and lysine salts may be present in protein hydrolyzates and these may be used as the source of lysine, provided that they contain sufficient to provide a palatability-enhancing amount of lysine without unduly affecting the nutritional balance of the product. Both the dand the 1- isomers of lysine improve palatability in accordance with the present invention; however, we prefer the l-isomer and its salts, particularly the hydrochlorides. Examples of salts of the lysines include l-lysine dihydrochloride, l-lysine monohydrochloride and d,l-lysine dihydrochloride. Of these we particularly prefer l-lysine monohydrochloride.

We have found that the use of lysine and salts thereof in accordance with the present invention provides a particularly significant improvement in the palatabilty of dry dog foods; however, an improvement in palatability may also be achieved with foods designed for other animals, including humans. For convenience, the invention is described largely in relation to dry dog foods; however, it will be appreciated that it may be applied to other dry foods, whose formulation and preparation will be well-known to those in the art.

There is no particular limitation upon the nature or ingredients of the dry dog food to which the present invention may be applied and any specific listing of such ingredients might well be misleading, since these vary greatly and will be entirely dependent upon the nutritional balance of the food desired as well as the availability and price to the petfood manufacturer.

In general, however, the food will comprise a mixture of proteinaceous and farinaceous ingredients chosen and/or processed to provide a dry product having a moisture content not greater than 20 % by weight and more commonly not greater than 15 % by weight. In addition to the principal proteinaceous and farinaceous ingredients, dry dog foods commonly include other nutritional additives, such as vitamins and minerals, and possibly other materials such as preservatives and emulsifiers.

In general, the term "proteinaceous material" is applied to a material having a protein content of at least 15% by weight, whereas the term "farinaceous material" is applied to a material having a protein content below this and containing a major proportion of starchy or carbohydrate-containing materials. However, the terms are not normally defined precisely and the skilled man would recognize whether a given material is proteinaceous or is farinaceous. Examples of proteinaceous materials commonly used in commercial petfoods, including dog foods, are: vegetable protein materials. particularly protein meals, such as soybean, cottonseed or peanut meals; animal proteins, such as casein or albumen; and, of course, meat tissue, including fresh meat, as well as rendered or dried "meals", such as fish meal, poultry meal, meat meal, and meat and bone meal. Other types of proteinaceous materials which may be used include microbial proteins, such as yeast, and other types of protein, such as wheat gluten or corn gluten.

Examples of commonly used farinaceous materials are grains, such as corn, alfalfa, wheat and soy hulls, and various other grains which are relatively low in protein. Numerous other materials can also be added to dog food compositions and do not necessarily fall into either the proteinaceous or the farinaceous category of ingredient; such materials include dried whey and other dairy by-products and carbohydrates.

Although, as noted above, there may be considerable variation in petfood composition, particularly from one manufacturer to another, peffoods are generally formulated for specific types of animal and products designed for a particular animal can often be recognized by their composition, particularly where such products are intended to be the animals sole food intake and thus need to be nutritionally balanced to maintain the animal effectively. Thus, there is a minimum protein level at which dogs will effectively be maintained when a dog food provides their sole food intake and commercially sold dog foods (with the possible exception of snack-type products, which may be formulated with less than the normal protein content) typically have a minimum protein content which is dependent upon the age of the animal and whether it is involved in breeding or reproduction. Accordingly dog foods designed for puppies or females involved in breeding would generally have a minimum protein content of 20% by weight and preferably a protein content of from 20 to 25 % by weight, whereas dogs not in either of the above categories would require a minimum protein level of 15% by weight. These figures are based on the assumption that the dog food will provide the sole food intake for dogs and thus commercial dog foods, with the possible exception of snack-type foods, normally have a minimum protein level of 15% by weight, in order to meet the nutritional requirements of any type of dog. It should, however, be noted that dog foods can and sometimes do, contain more than 25% by weight protein.

The percentages given above, as with all percentages expressing the proportions of constituents in the composition of the invention other than moisture, are on a 90% dry matter basis, based on the weight of the entire food composition. Moisture, is on an "as is" basis and is measured according to the Association of Analytical Chemists (AOAC) Procedure B, No.

7008, which involves weighing the product, heating it in an oven at 1300C and then reweighing to determine the moisture loss.

Cats typically require a higher protein content than do dogs and food products formulated for cats will thus generally have a protein level of at least 20% by weight, which is the minimum protein level required for mature cats not involved in reproduction. However, cats when breeding and kittens generally require a minimum protein level of 28% by weight; accordingly, most cat foods, when designed to be the sole food intake of the animal, have a protein content of at least 25% by weight and more preferably at least 30% by weight.

Accordingly, it is often possible to distinguish between cat and dog foods by reference to their protein contents, although this is not the only distinction between them.

Fat is typically included in commercial dog food compositions to provide an energy source for the animal and, because it improves the attractiveness and palatability of the food to the dog, fat is generally applied as a coating on the dried composition. However, although the presence of a fat coating when used in association with lysine in accordance with the present invention provides extremely good palatability, we have found that the improved palatability provided by the incorporation of lysine is not dependent upon the presence of added fat. The particular type of fat used is not critical and will generally depend upon availability and the desired free fatty acid content. Typical fats which may be used include lard and tallow. The particular level of fat employed is also not critical and, for dog food compositions, a typical fat level would be from 5 to 20% by weight.

As noted above, the preferred Iysines and salts thereof are l-lysine, d,l-lysine mixtures and salts and mixtures thereof. Of these, because of its ready availability, l-lysine monohydrochloride is preferred. The lysine or salt thereof is employed in an amount sufficient to enhance palatability and preferably in an amount of from 0.00008 to 0.5%by weight, more preferably about 0.1 % by weight, calculated as lysine and based on the overall weight of the composition. The lysine is preferably present on the surface of the composition but may be distributed throughout the composition, if desired. It should be noted that lysine is an amino acid constituent of proteins and could thus be expected to be present in most, if not all, proteinaceous food compositions, in such proteins. The amount of lysine added for palatability enhancement in accordance with the invention is in excess of that naturally present in such products or present to provide nutritional balance. The lysine or salt thereof may be in any physical form (e.g. solid or liquid, amorphous or crystalline) or purity and, where employed, for example, in the form of an aqueous solution of a salt, may be of any concentration, provided that the required amount of the lysine or salt thereof (as distinguished from its presence generally in proteinaceous materials) is present in the petfood composition.

After the food composition has been prepared, e.g. by expansion or extrusion, it is, if necessary, dried to the requisite moisture level, generally below 15 % by weight by means of forced air. The food composition is preferably in the form of separate particles commonly called "kibs". After drying, the composition is then conveyed, e.g. by a belt or other conveyor, through one or more spray chambers. If it is desired to apply lysine or a lysine salt and fat by separate sprayings successive spray chambers are provided. The lysine or lysine salt may be applied in any convenient manner but is preferably applied in aqueous solution after the fat has been added. The coated particles are then preferably tumbled in a drum to provide a more uniform coating, and they are then cooled to ambient temperature and packaged.

We have found that application of lysine or a lysine salt in this manner, particularly in an amount of from 0.00008 to 0.5 %, and preferably about 0.1%, by weight provides a statistically significant palatability response from dogs, as compared with an otherwise similar product which lacks the added lysine.

The statistical significance is suitably computed by the method of Wilcoxon. This method is a well-known test for determining the statistical significance of a behavioral response, such as an animal choosing to consume more of one particular type of food than another when the animal has ready access to both. This test was used in the following Examples and was carried out as follows: Method of Wilcoxon The animals used in this test were medium-sized adult healthy dogs. They were chosen from breeds including pointers, English setters, labradors, whippets and poodles, because such breeds have, after more than 50 years of research, been proven to have more sensitive and consistent palatability responses. Their taste preferences are a very reliable guide in predicting what the overall dog population will prefer; on the other hand, some breeds, e.g. beagles, are not, as a rule, very reliable. 20 dogs from the selected breeds mentioned above were placed in individual pens. Two bowls were placed in each dogs pen over 4 day intervals.

One bowl contained the sample to be tested (which had the added lysine palatability enhancer) and the other contained a control without the palatability enhancer but otherwise identical. Each bowl contained more than the dog could possibly eat during the interval of time in order that the dog would not -eat from one bowl merely because the other bowl was empty. Although the dogs were allowed to feed free choice, each day the position of the two bowls was switched in order to discount the possibility that a particular dog might be a position eater. Each dogs consumption was recorded individually. The differences between the amount of the control consumed and the amount of the sample donsumed (hereinafter referred to simply as the "difference") were recorded for each individual dog over the period of the test. Each difference was given a sign depending upon whether more of the control ( +) or more of the sample (-) was consumed. Then each difference was assigned a ranking between 1 and 20 (since there were 20 dogs, there were 20 differences) depending upon the magnitude of the difference but disregarding the sign. In other words, the smallest difference was assigned the rank 1, the next largest 2, and so on, regardless of whether the difference was + or -. In the event that more than one dog had the very same difference, then the rankings which would have been assigned to those differences were averaged; for example, if the three smallest differences were all of the same magnitude, then each difference would be assigned the average of 1, 2 and 3, i.e. 2. Next, each dogs ranking was given the sign which had previously been given to that particular difference. For example, if the dog having the lowest magnitude of consumption difference had consumed more of the control than of the sample, then its ranking of 1 would become + 1, which, of course, corresponds to the sign which had been recorded for that dogs consumption difference. Then the positive and negative rankings were totalled separately. Whichever total was the larger was used along with the number of dogs showing a preference as a key for determining the statistical significance from a Wilcoxon probability chart. This statistical analysis was, of course, performed separately for each sampel tested. The Wilcoxon signed rank test is believed to provide the most reliable statistical probability of whether, in fact, a prefereiice has been shown.

The invention is further illustrated by the following Examples.

EXAMPLES 1 To 10 Dried extruded kibs having a moisture content of 10.5 %, a protein content of 22.5 % and a farinaceous content of 62% at a temperature of about 1200F were carried from a drier to the top of a spray chamber by a belt conveyor. The kibs were dropped in a sheet from the conveyor belt and fell through the spray chamber. Spray heads located on both sides of the falling sheet sprayed a dispersion of melted tallow on the hot kibs as they fell through the spray chamber. Then a 1% aqueous solution of 1-lysine monohydrochloride at a temperature of 120"F was sprayed on the kibs to provide the amount of lysine monohydrochloride shown in Tables 1 and 2. The amount of monohydrochloride shown in Tables 1 and 2 is the actual amount of the salt and the amount of lysine itself would be 80% of the amount of monohydrochloride; thus. 0.001% lysine monohydrochloride means a lysine content of 0.0008% etc.

The spray-covered kibs were collected at the bottom of the spray chamber and were then conveyed to a tumbling drum. The kibs were tumbled at about 12 revolutions per minute for about 3 minutes. after which they were removed from the drum and cooled to ambient temperature. Similar kibs were also produced but without the l-lysine monohydrochloride.

The products were then fed to a group of dogs either wet or dry over a period of 4 days. The results were then assessed by the Method of Wilcoxon and the results are reported in Tables 1 and 2. Table 1 showing the results when the ration was fed dry and Table 2 showing the results when the ration was fed wet.

Table 1 Ration Fed Dry Ex. Composition Total Dogs preferring Dogs showing No. of Siguificance No. pounds (eating more of no prefer- Dogs consumed one than other) ence Control 16.1 2 1 Control + 0 20 P < 0.01 0.001% lysine HCl 37.5 18 Control 4.3 0 2 Control + 0.01% 0 20 P < 0.01 lysine HCl 27.8 20 Control 6.8 0 3 Control + 0.1% 40.9 20 0 20 P < 0.01 lysine HCl Control 16.3 1 4 Control + 0.5% 54.4 19 0 20 P < 0.01 lysine HCl Control 20.5 3 5 Control + 0.0005% 33.6 17 0 20 P < 0.01 lysine HCl Table 2 Ration Fed Wet Ex. Composition Total Dogs preferring Dogs showing No. of Significance No. pounds no prefer- Dogs consumed ence Control 27.5 3 6 Control + 0.001% 0 19 P < 0.01 lysine HCl 53.0 16 Control 47.8 8 7 Control + 0.01% 2 20 N.S. lysine HCl 61.1 10 Control 29.8 3 8 Control + 0.1% 0 20 P < 0.01 lysine HCl 75.2 17 Control 19.8 0 9 Control + 5% 0 20 P < 0.01 lysine HCl 110.5 20 Control 44.7 1 10 Control + 0.0001% 0 20 P < 0.01 lysine HCl 83.4 19 From the Tables, it can be seen that the inclusion of the lysine monohydrochloride markedly increases palatability. The dogs fed free choice often consumed three or four times as much of the product of the invention as they did of the control. The statistical significance (P < 0.01) indicates that there is less than merely a 1 %chancre that no behavioural preference was shown. In other words, more than 99 times out of 100, a dog would prefer the particular treated ration over the control. The abbreviation "N.S." means "not statistically significant", but in this case there was nonetheless a marked numerical preference for the composition of the invention.

EXAMPLE 11 Palatability tests were conducted with dog food samples containing a higher protein content, i.e. 26% by weight, with a commensurate reduction in farinaceous content. The samples also differ from those in Examples 1 - 10 in that the l-lysine monohydrochloride was added directly into the fat rather than on top of the fat. Otherwise, the samples were prepared as described in Examples 1 - 10 and the same Wilcoxon method was used to determine the statistical significance of the palatability response. The products produced in this Example were stored for varying periods of time to determine whether storage had any effect on the improvement in palatability. The results are shown in Table 3.

Table 3 Storage Composition Fed Pounds Dogs Dogs showing No. of Significance consumed preferring no preference dogs Control 30.0 8 5 days Control + 0.08% Dry 0 19 N.S. lysine 25.2 11 Control 34.2 4 5 days Control + 0.08% Wet 0 20 P < 0.1 lysine 50.4 16 Control 22.7 1 6 weeks Control + 0.08% Dry 0 18 P < 0.1 lysine 50.3 17 Control 49.0 6 6 weeks Control + 0.08% Wet 0 20 N.S. lysine 66.8 14 Control 30.3 7 3 months Control + 0.08% Dry 1 20 N.S. lysine 40.8 12 Control 65.8 5 3 months Control + 0.08% Wet 0 20 N.S. lysone 81.0 15 It was concluded from the data in this Table that, with the exception of one test (5 day storage, fed dry), a strong numerical preference was shown for the lysine samples and even a statistically significant preference was shown in two of the tests. Moreover, the preference pattern did not weaken with ageing. In fact, had the lysine been sprayed on top of the fat, as is more desirable, rather than directly with the fat, then the preferences would have been even stronger. Accordingly, six month and nine month normal storage tests were run using samples prepared in the same way to those used in Table 3 and the results are shown in Table 4.

Table 4 Storage Composition Fed Pounds Dogs Dogs showing No. of Significance consumed preferring no preference dogs Control 19.6 5 6 months Control + 0.08% Dry 0 20 P < 0.01 lysine 35.3 15 Control 31.0 0 6 months Control + 0.08% Wet 0 20 P < 0.01 lysine 87.0 20 Control 20.5 3 9 months Control + 0.08% Dry 1 20 P < 0.01 lysine 49.9 16 Control 51.4 3 9 months Control + 0.08% Wet 0 20 P < 0.01 lysine 88.3 17 These tests from material stored within the normal guaranteed storage term showed statistically significant preferences, both wet and dry. Thus, the shelf-life of the product with enhanced palatability is excellent. Moreover, these tests indicate that the palatability enhancement achieved by the use of lysine is, in the broadest sense, independent of the means by which the lysine is applied (either in the fat or on top of the fat) although it is preferred, for more consistent results, to spray the lysine on top of the fat coating. Also, the greater protein content did not affect flavour enhancement.

EXAMPLE 12 Dried kibs were produced as described in Examples 1 - 10, except that the lysine was replaced by either phosphoric acid or phosphoric acid and 0.075 %I-lysine. Phosphoric acid is used as a flavouring agent and is known to enhance the palatability of cat foods. The results are shown in Table 5.

Table 5 Composition Fed Pounds Dogs No. of Significance consumed preferring dogs Control 23.5 11 Control + Dry 20 N.S.

Phos. acid 24.4 9 Control 19.1 2 Control + Dry 19 P < 0.01 Phos. acid + 0.075 lysine 56.0 17 The results reported in this Table show that, rather than enhancing palatability, the phosphoric acid, if anything, detracted from palatability, whereas the addition of lysine did significantly enhance palatability and even overcame the negative effect of the phosphoric acid.

EXAMPLES 13 to 18 This test utilized lysine produced as a component of protein hydrolyzates. Two different types of hydrolyzates were used: one (Examples 13, 14 and 15) was a hydrochloric acid digest of casein, which had a free amino acid assay estimate of, inter alia, 12.8 mg lysine per gram; the second (Examples 16, 17 and 18) was an enzymatic digest of casein containing residual autolysates of pork gland and yeast resulting from the hydrolysis - it had a free amino acid assay of, inter alia, 64.6 mg lysine per gram. The hydrolyzates were applied by dusting onto a ration having the same nutritional composition as that of Examples 1 - 10. The consumption data are shown in Tables 6 (Examples 13,14 and 15) and 7 (Examples 16, 17 and 18). Even though the statistical significance was not measured, the excellent improvement in palatability can be seen from the measurement of grams consumed.

Table 6 Ex. No. Composition Grams Lysine amount consumed (weight %) Control 1686 13 Control + 0.1% 0.0013% hydrolysate 3584 Control 988 14 Control + 0.25% 0.0032% hydrolysate 4843 Control 1280 15 Control + 0.5% 0.0064% hydrolysate 5052 Table 7 Ex. No. Composition Grams Lysine amount consumed (weight %) Control 2406 16 Control + 0.1% 0.0064% hydrolysate 3989 Control 2281 17 Control + 0.25% 0.016% hydrolysate 5093 Control 1356 18 Control + 0.5% 0.32% hydrolysate 5269 EXAMPLE 19 This test was run with a control ration produced according to Example 11 and a test ration produced in accordance with Example 11, except that the lysine used was d-lysine monohydrochloride and it was sprayed over the fat as in Examples 1 - 10. The results are shown in Table 8, which indicates that the improvem

Claims (20)

Table 10 Composition Fed Grams Dogs Dogs no consumed I preferring preference Control 1367 5 Control + Dry 1 Lysine 2HC1 2437 10 WHAT WE CLAIM IS:

1. A dry food composition having added thereto, in an amount sufficient to enhance palatability, lysine or a salt thereof.

2. A composition according to Claim 1, in which said lysine is l-lysine.

3. A composition according to Claim 2, in which said salt is l-lysine monohydrochloride.

4. A composition according to Claim 1, in which said lysine is d-lysine or d,l-lysine.

5. A composition according to any one of the preceding Claims, in which the lysine or salt thereof is present as a component of a protein hydrolyzate.

6. A composition according to any one of the preceding Claims, having a protein content of at least 15% by weight on a 90% dry matter basis.

7. A composition according to Claim 6, in which said protein content is at least 20% by weight.

8. A composition according to Claim 7, in which said protein content is from 20 to 25% by weight.

9. A composition according to any one of the preceding Claims, containing at least 0.00008% by weight of said lysine or salt thereof.

10. A composition according to Claim 9, containing from 0.00008 to 0.5% by weight of said lysine or salt thereof.

11. A composition according to Claim 10, containing about 0.1 % by weight of said lysine or salt thereof.

12. A composition according to any one of the preceding Claims, in which said lysine or salt thereof is provided as a coating on the composition.

13. A composition according to any one of the preceding Claims, having a fat coating.

14. A composition according to Claim 13, in which said fat coating also contains said lysine or salt thereof.

15. A composition according to Claim 13, in which said lysine or salt thereof is provided as a coating over said fat coating.

16. A composition according to any one of the preceding Claims, in which said lysine or salt thereof is employed as an aqueous solution.

17. A composition according to any one of Claims 1 to 15, in which said lysine or salt thereof is employed in dry form.

18. A composition according to any one of the preceding Claims, having a moisture content not greater than 15% by weight.

19. A dog food composition according to any one of the preceding Claims.

20. A composition according to Claim 1, substantially as hereinbefore described with reference to any one of the foregoing Examples.