Link:  Pharm/Biotech Resources

Title:  Process for producing a product containing antihypertensive tripeptides

United States Patent:  6,972,282

Issued:  December 6, 2005

Inventors:  Tossavainen; Olli (Espoo, FI); Suomalainen; Tarja (Helsinki, FI); Sahlstein; Janne (Helsinki, FI); Mäyrä-Mäkinen; Annika (Helsinki, FI)

Assignee:  Valio Ltd. (Helsinki, FI)

Appl. No.:  111942

Filed:  October 30, 2000

PCT Filed:  October 30, 2000

PCT NO:  PCT/FI00/00942

371 Date:  May 7, 2002

102(e) Date:  May 7, 2002

PCT PUB.NO.:  WO01/32905

PCT PUB. Date:  May 10, 2001

The invention relates to a process for preparing a product containing antihypertensive peptides by fermenting a casein-containing starting material with lactic acid bacteria. The invention also relates to the obtained product and its use as a functional product as such or as an ingredient or additive of edible substances.

This application is the US national phase of international application PCT/FI00/0942 filed 30 Oct. 2002, which designated the US.

FIELD OF THE INVENTION

The invention relates to a process for preparing a product containing antihypertensive peptides. The invention also relates to the obtained product and its use as a functional product as such or as an ingredient or additive in edible substances.

BACKGROUND OF THE INVENTION

At present, cardiovascular diseases are counted among the most common national diseases in developed countries and their occurrence will further increase as the population grows older. High blood pressure contributes considerably to the development of these diseases. Therefore, treating hypertension is one of the most important measures regarding both prevention and effective treatment.

In blood pressure control, an angiotensin-I-converting enzyme, ACE, has a key role on a cell level. ACE functions in two ways: it converts angiotensin I to angiotensin II which is a strong vasopressor and inactivates bradykinin which, in turn, has a vasodilatory effect. Thus, both functions lead to elevated blood pressure. ACE inhibitors may inhibit this effect and consequently act as antihypertensive agents. Many known pharmaceuticals used in treatment of hypertension are ACE inhibitors. One of these is captopril, i.e. D-2-methyl-3-mercaptopropanoyl-L-proline, which is commercially available in Finland under trade names Capoten (by Bristol-Myers Squibb) and Captopril Generics (by Merck Generics).

Other methods to lower high blood pressure have also been sought as an alternative to medication, or in addition thereto. These include, for instance, to avoid obesity, to increase exercise and to consume a low-sodium diet. One of the newest ways is to use functional foods as a part of a normal diet, which the consumers have found to be a welcome alternative.

Fermented milk products have been reported to contain peptides having an antihypertensive effect. It is assumed that the peptides are produced in the milk products as a result of milk protein hydrolysis effected by lactic acid bacteria and particularly extracellular proteinases thereof. In J. Biochem. 114 (1993) 740, Yamamoto et al. describe purification and characterisation of a proteinase derived from the micro-organism Lactobacillus helveticus CP790. Yamamoto et al. have also reported on a study in which α_s1- and β-casein were hydrolysed with said proteinase and the obtained peptides were studied for their ACE-inhibitory effect (J Dairy Sci 77 (1994) 917). The studied peptides were 25 in total, and their molecular sizes and effects were greatly different. The most active ones were three peptides obtained from β-casein and containing 8, 18 and 27 amino acids respectively. The study also compared ACE-activity of milk fermented with the strain Lactobacillus helveticus CP790 and its variant CP791 with defective proteinase activity, whereby the former was found effective in spontaneously hypertensive SHR rats but not in an ordinary rat strain, whereas the latter had no activity at all.

In J Dairy Sci 78 (1995) 777-783, Nakamura et al. describe the use of a starter containing Lactobacillus helveticus and Saccharomyces cerevisiae for the preparation of two ACE inhibitors. Fat-free milk was fermented with said starter, whereafter the ACE inhibitors were purified chromatographically and analyzed. The active compounds were both tripeptides, Val-Pro-Pro and IIe-Pro-Pro. The publication does not describe an in vivo antihypertensive effect of the tripeptides and the sour milk product prepared with the starter, but it is mentioned to be the next subject of research.

U.S. Pat. No. 5,449,661 (Nakamura et al.) discloses the preparation of a peptide containing the tripeptide sequence Val-Pro-Pro and its use for lowering high blood pressure. The peptide is prepared by fermenting fat-free milk powder with the Lactobacillus helveticus strain JCM-1004, whereafter the peptide is purified chromatographically and freeze-dried.

International Patent Application WO99/16862 (Yamamoto et al) describes the Lactobacillus helveticus strain CM4, FERM BP-6060, which is capable of producing a large amount of the tripeptide Val-Pro-Pro and/or IIe-Pro-Pro and which exhibits a high extracellular protease activity. The publication also describes fermented milk products containing said tripeptides and bacterium, and a method for preparing them by fermenting products containing the tripeptide sequences with said bacterium.

Two disadvantages are associated with the products containing antihypertensive peptides prepared by fermentation reactions of lactic acid bacteria. The main product of fermentation is lactic acid, and it is produced the more the more effective the fermentation reaction. As appears from the term itself, lactic acid is acidic and gives a bitter taste to the product containing antihypertensive peptides, in addition to which many consumers find the high acidity and low pH unpleasant. A large number of monovalent ions, particularly sodium ions, are also present in the product containing antihypertensive peptides prepared by fermentation. These ions are known to elevate blood pressure, and hence they act in the opposite direction from the desired, antihypertensive peptides.

Prior art discloses methods of purifying peptides produced in fermentation. These methods allow to partly avoid the above disadvantages, while a concentrated product is obtained. However, the object of the prior art methods has been to provide pure products that are suitable for analyses and activity tests. Hence, the methods are multi-step methods that mainly consist of various chromatographic purifications and that are not suitable for large-scale production.

Therefore, there is still an obvious need to provide new functional products which have an antihypertensive effect and which the consumers find pleasant and familiar, and which therefore can be readily used as a part of the normal diet. It is important that the products do not contain unpleasant or even harmful components and that they are easy to produce on an industrial scale.

SUMMARY OF THE INVENTION

The object of the present invention is thus to provide a product having a high content of antihypertensive peptides and consequently having an antihypertensive effect.

Advantageously, in addition to the high content of antihypertensive peptides, the product of the invention has an advantageous salt content, which means that the amount of harmful monovalent cations is low and the amount of beneficial divalent cations is high as compared with a known product of similar type.

The object of the present invention is also to provide a process for preparing such a product, which process is simple and easy to carry out and therefore suitable for manufacturing the product on an industrial scale.

Further, the object of the present invention is to provide the product for use as such as an antihypertensive agent or in the manufacture of edible functional foods or pharmaceuticals.

In addition, the object of the present invention is to provide for use orally ingested products, such as functional foods and pharmaceuticals, which contain the above-described product as one of the active ingredients.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, it has been found that these objects can be achieved with a new process which is based on a new and inventive combination: a pre-preparation containing antihypertensive peptides is produced by fermentation, whereafter it is concentrated and the composition is finalized by nanofiltration. The combination according to the invention provides excellent possibilities to use starting materials of different types and to modify the composition of the end product to be of the desired type, as will be described in greater detail in the following.

Thus, the invention relates to a process for preparing a product containing antihypertensive peptides, the process being characterized by comprising the steps of fermenting a casein-containing starting material with a lactic acid bacterium and performing nanofiltration on the obtained, peptide-containing fermentation product.

The invention also relates to a product containing antihypertensive peptides, which product is characterized by having a high content of antihypertensive peptides and being prepared by a process in which the casein-containing starting material is fermented with a lactic acid bacterium and the obtained peptide-containing fermentation product is nanofiltrated.

The invention also relates to the use of the above-described product as an antihypertensive agent.

The invention further relates to the use of the above-described product in the manufacture of edible substances.

The invention also relates to edible products containing the above-mentioned concentrated product with high peptide content and conventional ingredients of said end products.

In the first step of the process according to the invention, a pre-preparation containing antihypertensive peptides is produced by fermentation. In fermentation, the starting material to be used can be any product which contains sequences of desired antihypertensive peptides as a part of their own peptide or protein sequence. Milk protein, particularly casein, is advantageously used as such or in the form of various preparations. Advantageously, suitable starting materials also include various casein-containing milk products, such as fat-free milk, or milk with varying fat content, as such or in the form of corresponding milk powder, and fermented milk products, such as sour milk, buttermilk, yogurt, curdled milk, unripened cheeses, etc.

Fermentation can be carried out with any lactic acid bacterium that is capable of producing antihypertensive tripeptides from the starting material. Suitable lactic acid bacteria can be found among species of e.g. Lactobacillus, Lactococcus, Leuconostoc, Streptococcus and Bifidobacterium genera. Lactobacillus helveticus is the most proteolytic of the lactic acid bacteria, and therefore it is considered particularly suitable for this purpose. An advantageous Lactobacillus helveticus strain is L. helveticus LBK-16H. Lactic acid bacteria can be used as pure cultures or mixed cultures, separately or with conventionally used and commercially available starters. Lactic acid bacteria can also be used together with other microorganisms. As regards combinations of microbes, appropriate combinations are selected to the effect that the best possible flavour is achieved in the end product and any contamination risk is avoided.

Fermentation conditions are selected to meet the requirements of the strain to be used in the fermentation such that a sufficient amount of antihypertensive peptides is formed to provide a desired effect. Selection of suitable conditions, such as temperature, pH and aeration, are part of the knowhow of a person skilled in the art. The temperature can be 30 to 45° C., for instance.

Fermentation is allowed to continue until the desired amount of antihypertensive peptides is formed. Normally, this takes about 20 to 30 hours, preferably 22 to 24 hours.

A mixture of various peptides is formed in fermentation. When fermentation takes sufficiently long, relatively small di- and tripeptides, such as Val-Pro-Pro (VPP) and IIe-Pro-Pro (IPP) are mainly obtained.

After fermentation, the cell suspension is recovered. It can be used as such in a next step, i.e. for separating and concentrating peptides. The cell suspension can also be concentrated, for instance, by evaporation or by drying it partly or completely, such as by spreading it onto a plate, drying and finally grinding it to well preservable dry powder.

In some cases, it may be appropriate to subject the fermented product to a pretreatment, for instance, to remove casein or all milk proteins therefrom prior to nanofiltration. The methods applicable to the pretreatment are known in the field and comprise e.g. various precipitation and filtration methods. One useful method comprises adjusting pH of the fermented product to a region where casein precipitates, e.g to 4.6 at a temperature of about 37° C., whereafter the precipitated casein is separated by means of a curd separator, a casein separating sieve, a decanter or by depositing or some other suitable method. A second method comprises ultrafiltration of the fermented product, at a pH of 3 to 3.5, whereby all proteins are retained on the membrane and the obtained permeate is nearly protein-free whey. Coprecipitation which produces nearly protein-free, peptide-containing whey can be achieved, for instance, with addition of CaCl₂, heat treatment or addition of acid. When necessary, possible casein dust is removed by centrifugation. Other substances, such as lactose, can also be removed prior to nanofiltration, for instance, by enzymatic hydrolysis or fermentation.

The fermentation product, which has possibly been pretreated in an appropriate manner, such as the whey obtained as described above, is then subjected to nanofiltration. A conventional NF membrane, such as Nanomax-50 (Millipore) or Desal 5 (Desal Inc., USA), can be used as the nanofiltration membrane, and the conditions are selected to meet the requirements and instructions of membrane manufacturers. Selection of the nanofiltration membrane type and process conditions contribute considerably to the composition of the resulting peptide fraction, in particular to the salt and sugar composition.

According to the invention, the nanofiltration is performed to a desired dry matter content or volumetric concentration ratio, which generally is as high as possible. The dry matter content is in the order of about 20 to 40% and the volumetric concentration ratio is about 5 to 20. The (whey) concentrate can be diluted with water, whereby more salts and lactic acid can be removed from the concentrate in nanofiltration. This is a simple and efficient way to adjust the amount of salts in the concentrate to the desired level.

Small peptides, such as the tripeptides IPP and VPP of about 350 D, formed in fermentation and having an effect on blood pressure, are completely retained by means of the nanofiltration membrane. The process of the invention also enables complete removal of lactose: prior to the nanofiltration step, lactose can be enzymatically degraded, whereby the major part of the monosaccharides are removed. In the nanofiltration, included in the process of the invention, lactic acid, small-molecular nitrogen compounds, such as urea, and monovalent salts also permeate the membrane. Hence, the peptide content of the product increases by means of the nanofiltration. Due to concentration, the content of divalent ions, in particular the desired calcium and magnesium ions, increase, whereas the relative proportion of monovalent ions, such as sodium, potassium and chloride ions, decreases. Particularly sodium ions are known to have a considerable effect on the fluid balance and blood pressure in the human body, and therefore a decrease in the amount of these harmful ions can be regarded as a very considerable advantage. Calcium and magnesium ions, in turn, are known to contribute to lowering the blood pressure, and a high content of these ions is considered very desirable.

Table 1 shows how the components in the pre-preparation formed in the fermentation step of the process according to the invention behave in the nanofiltration step. The composition is presented by way of example to illustrate the invention and it is produced by fermenting fat-free milk with a Lactobacillus helveticus strain. As clearly appears from the above description, also other products can be used as starting materials. Moreover, fermentation conditions, nanofiltration and other pretreatments and additional treatments, if any, contribute to the outcome, so the composition and the nanofiltration results of the end products may vary and differ from those presented herein.

The product concentrated for antihypertensive peptides and obtained by the process of the invention can be used as such as an antihypertensive agent. The product can also be dried and used in the form of a powder or a lyophilized preparation. In accordance with the present invention, the product is advantageously used in the manufacture of functional foods or other products, however.

In the present document, the term food is used in a broad sense covering all edible products which can be in solid, gelled or liquid form, and covering both ready-to-eat products and products to which the product of the invention is added in connection with consumption, as an additive or to be a constituent component of the product. For instance, foods can be products of dairy industry, meat processing industry, food processing industry, beverage industry, baking industry and confectionery industry. Typical products include milk products, such as yogurt, curdled milk, curd cheese, sour milk, buttermilk and other fermented milk beverages, unripened cheeses and ripened cheeses, snack fillings, etc. Beverages, such as whey beverages, fruit beverages and beers, constitute another important group.

The product obtained according to the invention is used in an amount sufficient to provide the desired, antihypertensive effect. The amount to be used depends significantly on the concentration degree of the whey, being e.g. 0.1 to 30%, preferably 5 to 15%, calculated from the weight of the end product.

Because the process of the invention, and in particular its nanofiltration step, provide a good framework for preparing a product of the desired type, it is also possible to reduce the contents of components having an adverse effect on taste or to remove said components completely and consequently to preserve or even improve the taste of the product.

The product containing antihypertensive peptides can be added to a food during the manufacturing process or to a ready-processed food. Said foods thus contain the above-described concentrated product containing antihypertensive peptides in addition to other ingredients that are conventional in such foods, and their taste and use completely correspond to those of the conventional products.

Thus, the two-step process according to the invention provides a product which has a considerably higher content of antihypertensive peptides than the products produced only by fermentation. Apart from the peptide content, the process also readily allows to adjust contents of salts and their mutual proportions to a desired level. In particular, it is possible to raise the content of desired divalent ions and to reduce the content of harmful monovalent ions. The process is simple and inexpensive, and it is well suited for large-scale production, and in this respect it differs from the prior art processes.

Moreover, it should be noted that the protein fraction obtained from the separation of casein or total protein can be used correspondingly in the manufacture of antihypertensive products, such as the above-described milk products or sausages, for instance. The process is thus highly economical on the whole.
 

Claim 1 of 24 Claims

1. A process for preparing a product containing at least one antihypertensive tripeptide comprising the steps of:

(a) fermenting a casein-containing starting material with a lactic acid bacterium to obtain a tripeptide-containing fermentation product, wherein said lactic acid bacterium is capable of producing at least one antihypertensive tripeptide;

(b) filtering said tripeptide-containing fermentation product by nanofiltration; and

(c) recovering a retentate of said nanofiltration to obtain the product containing at least one antihypertensive tripeptide.

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