REHYDRATABLE YEAST COMPOSITION

Abstract: A yeast rehydrating composition comprising a blend of sorbitan monostearate and at least one stearic compound having a maximum HLB value of 12.5 and wherein the sorbitan monostearate and stearic compound are present in the composition in a weight ratio of between 19:1 and 1:1. The composition is dissolved in water and added to a yeast slurry before drying of the yeast. The dried yeast composition rehydrates rapidly and homogeneously by adding water.

Description: Rehydratable Yeast Composition This invention relates to a composition for the rehydration of yeast, an active dry yeast and to a process for rehydrating yeast. Yeast is widely used in the food industry, most particularly in the making of bread. Yeast is supplied in both dry and paste forms, the dry form being preferred because of its longer shelf life. However, the yeast must be moist when used, and the dry form must therefore be rehydrated prior to use. As yeast is inherently hydrophobic, a rehydrator is generally necessary, this being a chemical compound added to yeast during the drying process, usually at the stage where a yeast slurry is finally converted to the dry form. The presence of the rehydrator makes rehydration possible. The rehydrators in universal use are sorbitan monostearate and glycerol monostearate, the former being more popular. In most countries the rehydrator is used alone, but - 2 - recently there has been marketed an "improved" rehydrator, this comprising sorbitan monostearate with a minor proportion of soya lecithin. It has now been found that sorbitan monostearate can in association with certain ingredients provide a highly efficacious rehydrator. There is therefore provided, according to the present invention, a yeast rehydrating composition, comprising a blend of sorbitan monostearate and at least one stearic compound having a maximum HLB value of 12.5 the sorbitan monostearate and the stearic compound being present in the composition in a weight ratio of between 19:1 and 1:1. In a further embodiment the invention also provides a dried yeast composition comprising from 0.5 to 2.0% by weight of the dried yeast of a composition which comprises sorbitan monostearate and at least one stearic compound having a maximum HLB value of 12.5, the sorbitan monostearate and the stearic compound being present in the weight ratio of from 19:1 to 1:1. There is also provided a process for the rehydration of dried yeast comprising the step of combining with water a dried yeast which comprises from 0.5% to 2.0% by weight of the dried yeast of a composition which comprises a blend of sodium monostearate and at least one stearic compound having a maximum HLB value of 12.5, the sorbitan monostearate and the stearic compound being present in the composition in the ratio of from 19:1 to 1:1. By "stearic compound" is meant a chemical compound which comprises at least one saturated C . „ fatty acid chain, or stearoyl group, of the type possessed by stearic acid. The fact that this compound must also have a maximum HLB of 12.5 (and - 3 - preferably between 5 and 12.5) means that the compound must also comprise some chemical entity, o group, which is water-soluble or -solvatable. Compounds of this nature may be ionic or non-ionic, but it has been found that the most effective stearic compounds are anionic. Typical examples of suitable stearic compounds include anionic compounds such as sodium stearoyl lactylate and non-ionic compounds such as sorbitan tristearate ethoxylate which may contain any suitable length ethoxyl chain, compounds having an average ethoxyl chain length of twenty ethyleneoxy units being preferred. The stearic compounds preferred for use in the compositions of the invention are anionic compounds and in particular sodium stearoyl lactylate. Sodium stearoyl lactylate is known as a dough conditioner and emulsifier (see for example "Bakers Digest", 42. (6) 38-42 (1968)) and has been suggested for use as a component in an emulsifier for active dried yeast (see "Research Disclosure", December 1983, 23606). However, the known art does not teach or suggest the advantageous properties of a combination of compounds such as sodium stearoyl lactylate and sorbitan monostearate as a yeast rehydrator . The term HLB value is used in this specification in its usual meaning of an expression of the Hydrophi le-Lipophi le balance of an emulsifier and is well known in the art of surface active agents. The sorbitan monostearate and the stearic compound must be present in the yeast rehydrating composition such that the weight ratio of monostearate to stearic compound lies between 19:1 _ 4 _ and 1:1. It is preferable that the stearic compound be present in smaller quantity than the sorbitan monostearate, and the preferred weight ratios of sorbitan monostearate to stearic compound are from 15:1 to 5:1 and more preferably between 9:1 and 5:1. It is permissible to blend more than one stearic compound with sorbitan monostearate to produce a yeast rehydrating composition according to the invention. It is also permissible to include other additives, provided that these do not make up more than 15% by weight of the total composition. Preferred additives are antioxidants such as ascorbic acid and erythorbates used at a rate of from 5-15% by weight of the total composition. The compositions of the invention may be prepared by simply blending together the components using standard equipment. Some stearic compounds lend themselves more readily to processing than others. For example, solids which can be obtained as a powder such as sodium stearoyl lactylate are more easily blended with the sorbitan monostearate. In use, the composition is dissolved in water, typically as a 10-15% (wt) solution in which form it may be added to a yeast slurry prior to the drying of the yeast. When rehydration is required-, it has been found that dried yeast treated with a composition according to this invention rehydrates quickly and homogeneously. The rehydrating compositions of this invention give rise to a number of other advantages. For example, it has been found that in the drying process when dried yeast is formed from a slurry, the yeast to which such a composition has been added may dry more quickly and/or at lower temperatures than one to which sorbitan monostearate alone has been added. This makes the process more economic and gives a product which when rehydrated is more active than a yeast made using sorbitan monostearate alone. In addition, the storage stability of dried yeast using a rehydrating composition according to the invention is superior to that of the known dried yeasts . The invention is further described with reference to the following Examples. Exa p les Preparation of a composition according to the invention and comparison with known rehydrating composi tions . Three yeast rehydrating compositions were prepared as Comparative Examples using the following materials and quantities (expressed as parts by weight ) : Comp- Comp- Comp¬ arative arative arative Example Example Example Compos ition Cl C2 C3 Sorbitan monostearate 100 80 90 Soya lecithin - 10 - Sodium stearoyl lactylate - Sodium erythorbate - 10 10 Composition No. 1 is thus the yeast rehydrating composition in widespread use throughout the world, Composition No. 2 corresponds to the most recent European commercial composition and Composition No. 3 is Composition No. 1 with added aπtioxidant. Three examples of yeast rehydrating compositions of the invention were prepared using the following materials and quantities (expressed as parts by weight) : Composition Example No. El E2 E3 Sorbitan monostearate 80 80 90 Sodium stearoyl lactylate 10 10 10 Sodium erythorbate 10 - - Asorbic acid - 10 - Each of the above compositions were added to different samples of a batch of yeast to be dried at the stage of conversion of a slurry to the dry form. The Comparative Example Cl was taken as the standard and the others were compared with it in respect of drying time during production and yeast activity. The results were as follows: Comparison with Comparative Example Cl Example Drying Initial Yeast Activity No. Time Yeast after Storage The advantages of the rehydrating composition of the present invention can clearly be seen.

Claims: The claims defining the invention are as follows: 1. A yeast rehydrating composition comprising a blend of sorbitan monostearate and at least one stearic compound comprising one or more saturated C.g fatty acid chains of the type possessed by stearic acid which stearic compound has a maximum HLB value of 12.5 and wherein the sorbitan monostearate and stearic compound are present in the composition in a weight ratio of between 19:1 and 1:1. 2. A dried yeast composition comprising from 0.5 to 2.0% by weight of the dried yeast of a composition which comprises sorbitan monostearate and at least one stearic compound comprising one or more saturated C, g fatty acid chains of the type possessed by stearic acid which stearic compound has a maximum HLB value of 12.5 and wherein the sorbitan monostearate and stearic compound are present in the composition in a weight ratio of between 9:1 and 1:1. 3. A composition according to claim 1 or claim 2 wherein the stearic compound is an anionic compound . 4. A composition according to claim 1 or claim 2 wherein the stearic compound is a non-ionic compound. 5. A composition according to any one of claims 1 to 4 inclusive wherein the stearic compound has a HLB value in the range of from 5 to 12.5. 6. A composition according to any one of claims 1 to 3 inclusive wherein the stearic compound is sodium stearoyl lactylate. 7. A composition according to any one of claiim i s 1, 2 or 4 wherein the stearic compound is a sorbitan tristearate ethoxylate. 8. A composition according to any one of claims 1 to 7 inclusive wherein the sorbitan monostearate and the stearic compound are present in a weight ratio of between 15:1 and 5:1. 9. A composition according to any one of Claims 1 to 8 inclusive comprising, in addition to the sorbitan monostearate and stearic compound components, an antioxidant. 10. A composition according to Claim 9 wherein the antioxidant is selected from asorbic acid and erythorbates . 11. A composition according to Claim 8 wherein the antioxidant is present in an amount of from 5-15% by weight of the total composition. 12. A process for the rehydration of dried yeast comprising the step of combining with water a dried yeast composition comprising from 0.5 to 2.0% of weight of the dried yeast of a composition which comprises sorbitan monostearate and at least one stearic compound comprising one or more saturated C.g fatty acid chains of the type possessed by stearic acid which stearic compound has a maximum HLB value of 12.5 and wherein the sorbitan monostearate and stearic compound are present in the composition in a weight ratio of between 9:1 and 1:1. 13. A yeast rehydrating composition according to Claim 1 substantially as herein described with reference to the Examples. 14. A dried yeast composition according to Claim 2 substantially as herein described with reference to the Examples. 15. A process for the rehydration of dried yeast according to Claim 12 substantially as herein described with reference to the examples.

Inventors: JOHNSTON MICHAEL, LOMBARD ANNE, JOHNSTON, MICHAEL, LOMBARD, ANNE
Applicants: ICI AUSTRALIA OPERATIONS, ICI AUSTRALIA OPERATIONS PROPRIETARY LIMITED
Application year: 1991
Main classification: B01F17
IPC codes: A21D8, C12N1