Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
1997-07-11
2002-06-18
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S003000, C536S123000, C536S002000, C514S054000, C426S658000
Reexamination Certificate
active
06407226
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns the use of guluronic acid-rich alginates or galacturonic acid-rich pectins, so-called G-block polysaccharides, as modulator for the rheology in a mixture in which a gelling, water-soluble polysaccharide is a component which is intended to give the final product a changed viscosity, stability, elasticity, rigidity or similar.
Alginates are isolated from marine brown algae. Alginate is also produced in soil bacteria such as
Azotobacter vinelandii
and
Azotobacter crococcum
and many different Pseudomonas bacteria, but the commercially available alginate stems mainly from brown algae.
Pectins can be isolated from many different sources as it is found in the cell walls of fruit and vegetables, but the commercially available pectins are usually isolated from apples or citrus fruits.
These polysaccharides, alginate and pectin, are used in foods and in pharmaceutical, dental, cosmetic and other industrial products. The most common industrial uses are based on their hydrocolloid and polyelectrolytic nature, which forms the basis for the gelling, thickening, stabilising, swelling and viscosity-producing properties.
In foods such as jam, ice cream, packet soups and sauces, polysaccharides have a thickening, stabilising effect. In mayonnaises and dressings, they also act as an emulsion stabiliser.
In products such as baking creams and tinned pet food, the ability of alginate to form thermally stable gels, which are produced and hardened at room temperature, is used.
There is also great potential for the use of alginate in biotechnological and medical applications. Examples of this are the mass production of alginate-based solid nutrient medium for plant tissue cultures, alginate as an administration medium with slow release of a drug and encapsulation of live insulin-producing cells in alginate gel for implantation in patients.
Alginates are salts of alginic acid, a linear heteropolysaccharide consisting of (1→4) linked &bgr;-D-mannuronic acid, designated M, and &agr;-L-guluronic acid, designated G. These two uronic acids have the following formulae:
The polymers exist as homopolymer sequences of mannuronic acid, called M blocks, homopolymer guluronic acid sequences, called G blocks, and mixed sequences of mannuronic acid and guluronic acid units, so-called MG blocks or alternating blocks.
In order to illustrate the structure of the alginates, we show a schematic representation of a possible block structure.
Usually, alginate contains all three types of blocks and a block generally consists of three to thirty monomer units. The distribution of blocks depends on the type of algae from which the alginate is isolated as well as the age and part of the plant, for example alginate from the stem may have a different sequence and block composition to alginate isolated from the leaves. The season in which the algae are harvested also affects the block composition and sequence. On the basis of our present knowledge, the maximum G content in the stem is to be found in old
L. hyperborea
. Leaves from the same species have a somewhat lower G content and shorter G blocks, but the content is still higher than in most other species. The commercially available alginates usually have a G content of 25%-70%. Pectin has a complex structure with a polysaccharide chain in which “smooth” and “hairy” regions alternate. The smooth regions consist of non-dendritic (1→4) inked &agr;-D-galacturonic acid with the following formula:
with some (1→2) linked L-rhamnose, while the hairy regions are very dendritic and consist mainly of (1→3) and (1→6) linked &bgr;-D-galactose, (1→3) linked arabinose and some (1→3) linked xylose. The galacturonic acid groups are partially methoxylated.
In the following &agr;-D-galacturonic acids are designated G units, and the regions which mainly consist of such G units are designated G blocks. Thus guluronic acid blocks from alginate and galacturonic acid blocks from pectin come under this common designation in the following.
Below we show a schematic representation of a possible pectin structure:
Alkali metal salts, magnesium salts and ammonium salts of alginates and pectins are water-soluble. By adding multivalent cations, for example multivalent ions such as Ca
2+
, Sr
2+
, Ba
2+
, Fe
3+
or Al
3+
ions, to a polysaccharide solution, a gel is formed as a result of the production of ionic cross-links of several polysaccharide chains. The G units are responsible for the ability of these polysaccharides to link multivalent cations and this leads to the G blocks functioning as bindingseats between the various polysaccharide chains in connection with gelling.
The gel strength of polysaccharide gels will depend on various parameters such as the G content of the alginate or pectin, the length of the G blocks, the calcium activity and the molecular weight and concentration of the polysaccharides.
2. Description of the Related Art
Reference is made to “Food Polysaccharides and their applications”, Ed. Alistair M. Stephen, [1995] Chap. 9: “Alginates”, S. T. Moe, K. I. Draget, G. Skjåk-Bræk and O. Smidsrød, pp. 245-286, and Chap. 10: “Pectins”, A. G. J. Voragen, W. Pilnik, J. F. Thibault, M. A. V. Axelos and C. M. G. C. Renard, pp. 287-339.
These overview articles are to be considered to be included in their entirety.
If you react a water-soluble polysaccharide in solution with an easily soluble Ca salt, you will get an undesirable, lumpy consistency of gel or gel balls, depending on the procedure. In the preparation of continuous gels, it has, therefore, been common to use either dialysis or in situ gelling methods.
In dialysis, the cross-linking ion, usually calcium, diffuses into the polysaccharide solution and this then produces a continuous, inhomogeneous gel which is strongest near the diffusion surface.
In in situ gelling, the calcium ions are released inside the polysaccharide solution. An inactive form of calcium has been used together with an agent which makes possible a slow release of the ion, which produces a homogeneous gel and the gelling speed can be controlled. It has been common to use sequestering agents such as citrate, phosphate or EDTA to achieve controlled release of the cross-linking ion.
Alternatively, insoluble salts or salts which are hard to dissolve such as calcium sulphate or calcium carbonate have been used. In connection with the addition of an agent which makes possible a slow release of protons and thus a slow release of calcium ions, the gelling speed can be controlled. An example of such an agent is D-glucono-&dgr;-lactone (GDL).
Another possibility, which is used in tooth filling masses, is to replace the lactone with a system consisting of acid, base and a buffer. The buffer (Na
4
P
2
O
7
) reduces the gelling speed by initially linking the calcium ions which are released from the calcium sulphate. This produces a self-gelling system in which the gelling is started when water is added at the user's premises.
From U.S. Pat. Nos. 2,441,720 and 2,918,375 (Kelco Company), a procedure is known for the production of alginate gel in which a water-soluble alginate salt (usually potassium or sodium alginate) is converted with a calcium salt which is hard to dissolve such as tricalcium phosphate or calcium tartrate. In these systems, the calcium ions are released by means of acid or acidifying agents. The reaction speed of the reaction between the calcium ion and the water-soluble alginate is controlled by means of a gel-delaying or gel-inhibiting agent such as sodium hexametaphosphate.
In U.S. Pat. No. 3,060,032 (General Foods Corp.), calcium alginate gel is used to improve the freeze-thaw stability in frozen dessert jellies. This calcium alginate gel is produced from sodium alginate, calcium tartrate and sodium hexametaphosphate. The reaction speed of the reaction between the calcium ions, which are released from the tartrate, and the sodium alginate is controlled by means of the sodium hexametaphospha
Draget Kurt Ingar
Fjæreide Therese
Onsøyen Edvar
Simensen Merethe Kamfjord
Smidsrød Olav
FMC Biopolymer AS
Geist Gary
White Everett
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