The present invention relates to milk substitutes in powder- form which when mixed with an appropriate quantity of water provide a milk-like liquid suitable for feeding to mammalian young such as calves, lambs and piglets.

Conventional milk substitutes are generally ^" based on skimmed milk powder and fat, fortified with added minerals, vitamins, growth pro otors and other minor ingredients. Whey powder, and noή-milk proteins such as soya protein, can be included. These conventional milk substitutes have excellent nutritional properties, but in practice suffer from the defect that following reconstitution with water they acidify through bacterial action and this leads to undesirable coagulation. The maximum time that such a milk substitute can be left unconsumed after reconstitution during the summer is J6 hours, and if a residue.of this unconsumed material i allowed to remain in a storage vessel which is topped uυ

> with freshly reconstituted milk substitute, the mixture will be unusable within a further 24- hours. In faτττπτ-tg situations this problem of spoilage increases labour costs because the stockman must clean out his storage vessels and replenish them with freshly reconstituted milk substitute on a daily basis, in order to ensure that his animals are receiving uncoagulated feed. The consequences of not maintaining such a strict regime are poor feed intakes and poor feed conversions, and a constant ris ---of serious gastro-intestinal infections (scouring) which can further retard growth or even lead to death. Further coagulation of the eed can. cause blockage of teats and other feeding mechanisms. Also, the unattractive appear¬ ance of the coagulated feed may cause the careful stockman to discard the feed prematurely even though bacteriologically it could still be fed safely to the animals.

' -A recent development has been the marketing of milk substitutes which incorporate mixtures of edible organic acids and salts of such acids which appear to impart longer storage li e after reconstit¬ ution. These acidified milk substitutes are all based principally on whey powder, and contain only minor amounts of skimmed milk powder or caseinates. Clearly it would be beneficial to enhance similarly the storage life of milk substitutes that contain substantial amounts of milk powder or caseinates. Advantage could thus be taken of the ready availability of skimmed milk powder, of which there is currently an embarassing surplus. However, the addition of acids to milk substitutes containing milk powder

could cause immediate coagulation of casein on reconstitution. Coagulation of casein is known to occur at pH 4.7 and below, but even where the nominal pH of the reconstituted product is higher than 4.7 it is possible that localise concent¬ ration of high acidity could occur during recon¬ stitution, leading to the development of curds- In the ormulation of an acidi ied milk substitute containing substantial amounts of casein it is essential therefore to ensure that the occurence of any such local concentrations is minimised,.

By the present invention we are able to provide a milk substitute in the form of an unreconstituted powder containing by weight more than ^' 10% casein which does not exhibit significant casein coagulation on reconstitution and which has after reconstitution a storage life, at the typical ambient temperatures encountered in temperate latitudes, of more than 36 hours. iPurther, the invention can provide such a milk substitute having a storage life after recon¬ stitution of more than 48 hours, and even as long as 3 to 4 days. Moreover, by the invention we are able to provide milk substitutes having such improved storage capacilities after reconstitution in which the casein level is at least 15% _» ^a - ^α - ⁽ i even 20% or more, by weight.

A particular embodiment of the invention is _a milk ^' substitute in the form of an unreconstituted pow¬ der containing, by weight, more than 10% casein, an acid-responsive food grade preservative, and an edible acidifying system that generates a pH value

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in the milk substitute immediately after reconstitut ion in the range 6.0 to 5 _* 2, preferably 5-9 to 5- 3- aαd ideally .6 to - -.

The invention includes a method of rearing youn mammalian animals, such as calves, wherein the anima are provided on an individual or group basis with a quantity of liquid eed reconstituted from a milk substitute of the invention, the liquid eed being presented in a manner such that the animals _. can drin ad lib thereof and the quantity being sufficient to sustain the animals for a period of more than 36 hou preferably from 3 to 4 days.

By an acid-responsive preservative we mean a pr servative the effectiveness of which increases as pH decreases. The most preferred preservatives are water-soluble propionates, ideally present as sodium or calcium salts. Alternatives are acetates and fo formates. In general the preservatives will compri at least 0.5%-, ^~ £-<- ideally at least 1%, by weight of the milk substitute. In general, the preservative will not comprises more than 5%, &■- typically not more than 2%, by weight of.the milk substitute. Mixtures of two or more preservatives can be used if desired, the above percentages than being taken as indicating the total preservative content of the mil substitute. In addition, preservatives that are no acid-responsive can be incorporated, paraformaldehyd being an example. For flavour and aroma reasons, ' it is preferable that only trace amounts of formalde hyde-generating preservatives should be used, typica comprising not more than 0.2% by weight of the milk substitute.

The edible acidifying system can comprise one or more readily water-soluble solid, preferably crystalline, organic acids, such as malic acid, ^• citric acid or tartaric acid. Malic acid is the most preferred. Fumaric acid can also be used, but tends not to be as readily water-soluble as the acids already mentioned and can lead to mixing problems when the milk substitute is reconstituted; it is therefore not preferred. These solid acids are particularly suitable for use in milk substitutes whose manu acture involves the dry mixing of their individual ingredients. ^" Alternatively, or in addition, certain edible liquid organic acids can be used in minor amounts, ^' these being blended with dry ingredients or added to milk prior to the production of miIk ^* powder by spray-drying. Suitable liquid acids include ormic acid and acetic acid. The total quantity of acid present will generally lie in the range 0.1 to 2% by weight of the milk substitute.

For nutritional reasons it is often desirable to include phosphate in a milk substitute. Generally this is included in conventional milk substitutes as calcium hydrogen phosphate, despite the fact that it is relatively insoluble in water. However, in the context of the present invention, ideally calcium hydrogen phosphate should be omitted entirely, and ^■ if used at all it should be kept on an absolute mini¬ mum. We prefer to use water-soluble phosphates, part¬ icularly as these appear to assist in preventing coagulation of the high-casein milk substitutes of _. the invention. Sodium dihydrogen phosphate is most preferred. Disodium hydrogen -phosphate can also be used, either alone or in a buffering combination with sodium dihydrogen phosphate. Generally the soluble

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phosphate need not comprise more than 2% by weight of the mil substitute.

A most pre erred embodiment of the invention is a milk substitute in the form of an unreconstitut powder containing, by weight more than 10% casein, r 0-5 to 2%, preferably 0.5 to 1.5% _» calcium prop¬ ionate, from 0.1 to 2%, preferably 0.1 to 1%, malic acid and from 0.1 to 1.5% sodium dihydrogen phosphat

In addition to the acid-responsive edible preservative and edible ^' acidifying system, and phosphate when present, a milk substitute in accord¬ ance with the invention can contain any of the stand ard ingredients used in conventional milk substitute Typically these are 50 to 80% skimmed, milk powder, 10 to 25% fat, 0. to 30% of spray-dried whey powder and/or non-milk proteins such as soya protein, fish meal, single-cell protein and legume meal, and a total of up to 10% minerals, vitamins and other minor additives.

All percentages given throughout this specific¬ ation are expressed by weight of the milk substitute in the form of an unreconstituted powder because this is the physical form in which milk substitutes are sold commercially. Reconstitution of the milk substitute into a drinkable product for feeding to young mammalian animals will entail mixing the dry powder with an appropriate quantity of water in the conventional manner. As a precaution against casein coagulation, it is sensible to avoid the use of hot water in the reconstitution of the milk sub¬ stitute, and therefore water _. at a temperature below 50 C is reccommended. Cold water can be used.

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Typically the quantity of the dry pov/der used will be 80 to 200 g per litre of water.

Manufacture of a milk substitute of the invent¬ ion can be accomplished .by. simple dry mixing of the ^' individual ingredients. Alternatively, the ingredients can be added to liquid milk prior to the conventional spr*?y-drying of milk to yield milk powder.

The invention is illustrated by the following Examples.

Example 1

. A milk substitute for calves, based on fat-filled skimmed milk powder, was prepared by dry mixing and contained, by weight, 17.0% casein, 6.0% whey protein, 45% lactose, 17-0% fat, 1.5% calcium ^' prop¬ ionate, 0.6% malic acid, 0.5% sodium dihydrogen phos¬ phate monohydrate, 0.05% "Payzone" (a commercially- available growth promoting additive containing by weight thereof 5% nitrovin, which may have some beneficial enhancing effect on the preservation system of the invention) and sundry conventional minerals, vitamins and moisture. The milk sub¬ stitute was reconstituted in tap water at 40°C, at a level of 125 g per litre of water. . After thor- ough mixing, the minimum pH recorded was 5-50 and the reconstituted product had a normal un-coagulated milk- like appearance. The pH was recorded as 5-86 two hours later. After standing at ambient temperature (approximately 20 C) for 3 days, the pH of the product had dropped to 5-31- After a further 24 hours the pH was 5-16, but throughout the period the product remained un-coagulated and looked and smelled whole¬ some.

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Comparative Example

In contrast, a milk substitute of essentially similar formulation but containing no calcium prop¬ ionate or malic acid, reconstituted in exactly the same manner and at the same time, and stored under- identical conditions, had within two days the appea ance and smell of a product obviously spoiled by mi biological activity.

Example 2

milk substitute for calves, of formulation similar to that of Example 1 but containing malic acid at a level.,of 0.5% by weight instead of 0.6%, was reconstituted and stored under conditions stric comparable with those applied in Example 1. The lowest pH recorded immediately following reconstitu ion was 5-50. After three days the pH of the prod was 5 _* 20, but the product was still uncoagulated an fully satis actory in all respect.

Examples 3 an 4

. Two milk substitutes for calves of formulat¬ ions similar to that of Example 1, but containing citric acid (Example 3) and fumaric acid (Example 4 respectively at a level of 0.6% in place of the mal acid, were reconstituted and stored under condition strictly comparable with those applied in Example 1

The milk substitute of Example 3, containing citric acid, began to sour after 3 days, but was entirely satisfactory up to that time.

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The milk substitute of Example 4, containing fumaric acid, exhibited some scum ormation on initial mixing, but in terms of freedom from scour- ^• ing was equal to the milk substitute of Example 1. The sum formation appeared to be due. to an inter¬ action between the fumaric acid and the at in the formulation. This slight problem did not occur when the milk substitute was reconstituted using cool (below 18°C) water.

Example 5

A milk substitute for calves, based on fat- filled skimmed ^' milk powder, was prepared by dry mixing and contained, by weight, 17.0% casein, 6.0% whey powder, 45% lactose, 17.0% fat, 1.5% .calcium propionate as preservative, 0.3% malic acid, plus sundry minerals, vitam ns and moisture. ΪFo phosphate was present. ^■ The milk substitute was reconstituted and stored as in Example 1. This product reconstituted smoothly without any signif- icant casein precipitation and had an initial pH of 5.4. It remained uncoagulated and whole-some for over three days.

Examples 6 to 8

Three milk substitutes for calves, each having a formulation identical to that of Example 1, with the exception that the added phosphate salt content was as indicated below, were reconstituted and stored as in Example 1.

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Ex.6 Ex.7 Ex.8

NaH ₂ P0 (% 0.4 0.3 ^' 0.2

ITa ₂ HP0 _Zi _(%) 0.1 0.2 0.3

Total 0.5 0.5 0.5

Compared to the performance of the milk sub¬ stitute of Example 1, which contained 0.5% of sodiu dihydrogen phosphate only, these three -formulations showed a slight tendency to curdle on reconstitutio increasing with increasing proportion of the disodi salt. Nevertheless, each formulation was consider to be acceptable from this point of view. . As expe from the relatively more alkaline nature of the dis salt, the formulations of Examples 7 an 8 had sl higher initial pH values immediately following reco stitution, but in performance terms the storage lif of each reconstituted product was satisfactory as e lasted for more than three days before any serious souring became evident.

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