CA1063104A - Method for treating seaweed with hydrogen peroxide or hydrogen peroxide compound - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method is disclosed for stripping off outer skin of seaweed with hydrogen peroxide or hydrogen peroxide compound, which is suitable for use in preparing seaweed powder or algin from the seaweed.

Description

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This invention relates to a method for treating sea- ~
weed, more specifically to a method for stripping of~ outer ;
skin (e~odermis) of the seaweed for preparing seaweed-powder or algin.
Although various seaweeds, such as Laminaria or Undaria pinnatifida, have provided sources of useful alkali foods for human consumption since ancient ages, in their natural forms these plants themselves are not necessarily suitable as foods.
For example, seaweed products commonly marketed are prepared by simply drying the natural seaweed. As these products ha~e the ~
seaweed skin intact, they are bad in appearance, being dull in ~; , tone and giving the impression of being unclean. Furthermore, they are difficult to digest. Seaweeds are also boiled to pro- ;
duce soup base and stock concentrates. However, naturally avail-able seaweed ls disadvantageous in producing such concentrates since the skins thereof impair the quality as well as digestibility of the soups and stocks prepared from the concentrates.
As another application of seaweeds, there must be mentioned the preparation of algin therefrom.
Alginic acid, a kind of mannuronan belonging to the polyuronide family, is a linear molecule composed of D-mannuroic acid having ~ bonds therein. This acid is an important constitution polysaccharide which is contained in seaweeds, par- ;
ticularly in phaephyta. Algin is the generic name of various `::
salts of alginic acid and the sodium salt, ammonium salt and propyleneglycohol ester of alginic acid are of particular com-mercial significance.
Although algin has a variety of applications, because of its excellent emulsifying, stabilizing and water-absorbing actions, such as jellying agent, water-soluble ointment, lubricant, paper-sizing agent, finishing agent for leather or fabrics, and even pasting agent and childbirth-assisting agent, it is e~tremely .~
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1~3t;3~L~4 troublesome to handle because of its high viscosity (1000 centi~
poise at 1% solution, ~000 centipoise at 2% solution). The ~ `
conventional method for recovering algin from seaweeds i9 thus `~
disadvantageous in that it comprises compl:icated processing steps and requires a long time thus result:ing in high cost which has prevented the wide usage of said method.
The following is an example of a complicated method .
conventionally practised.
Seaweed such as tangle, after being washed with water, is swelling-treated for several hours, for example, with 0.05N
sulfuric acid, and then is added with caustic soda or soda ash ; followed by stirring of the mixture for over five hours at pH
of approx. 9.5. The solution thus obtained is highly viscous, and is diluted with water for lowering the viscosity to prepare , a diluted solution of algin, for example, of 0.85 g/l. (The dilution step is indispensable in the conventional method.) A
f-iltration step follows. However, the solution is difficult to filter per se. Filtration is carried out after the insoluble .. :: ~
residue composed of such as the outer skins of the seaweed is removed from the solution with wire-netting using a filtration-assisting agent such as diatom earth. The filtrate is there-after neutralized ~ith sulfuric acid to produce alginic acid, ~ which is then taken up by floatation method for preparing a solu--` tion, for example, of 2%. The solution is further neutralized with alkalin, the resulting gel being decolored and dehydrated over a long period of time~ The final product is obtained by repeating these steps several times.
As explained in the above, the conventional method for - recovering algin from seaweed is disadvantageous since it requires a number of troublesome steps due to the high viscosity of alginic acid and its salts, and particularly requires a step for removing .. . .

~ impurities such as the outer skins from the seaweeds or a step .- .; .
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~ - 2 -: :, 1~631~4 for decoloring the hlyhly ViscQus extract product of the seaweeds.
An attempt to avoid the lligh viscosity by heating fails since it causes considerable change in chemical structure of the compounds.
For exarnple, heat treatmenk for an hour at 95C gives rise to 37% lowering in viscosity, and that for an houx even at 80C
give rise to 8% lowering in viscosity, ind:icating substantial .
change in chemical structure.
Accordingly, it is an object of the present invention to provide a method for concisely and cheaply preparing edible seaweed powder and algin. ;
The present invention is based on the finding that . addition of hydrogen peroxide or a hydrogen peroxide compound (a compound to be decomposed to produce hydrogen peroxide), per se or in a suitable solution, into protoplasmic aqueous solution of seaweed ~eyardless oE whether alkaline, neutral or acidic) will accelerate stripping-off of the outer skin of the seaweed ~:
because of permeability through the skin of the seaweed by hydrogen peroxide and the function of enzymes such as catalase present mainly in the middle of the exodermis layer and the endo-dormis layer.
The present invention thus provides a method for pre-paring seaweed powder which comprises adding hydrogen peroxide .
or a hydrogen peroxide compound to seaweed to strip off the outer skin of the seaweed and then drying the seaweed which has been :-removed of its outer s]cin. ~ -The preseni invention further provides a method for ` preparing algin which comprises adding hydrogen peroxide or a hydrogen peroxide compound to strip off the outer skin of the seaweed, alkaline-treating the seaweed which has be0n stripped of :~ :
its outer skin to convert alginic acid contained in the seaweed into alkali alginate, and recovering the alkali alginate.

According to the present invention, hydrogen peroxide -- 3 _ 6310~L ~
or hydrogen peroxide compound added is decomposed to produce atomic or molecular oxygen by the function of an enzyme such as ;
catalase, said oxygen facilitating the stripping of the outer skin of the seaweed and at the same tirne bleaching the contents of the seaweed.
The seaweed thus can be efficiently converted, by simple drying process, into extremely clean seaweed powder. In addition to its colorless cleanness, the seaweed powder obtained by the present invention is advantageous in that it has excellent ~ , digestibility since the stiff, indigestible outer skins have been ~ . :
stripped off. The seaweed powder obtained by the present inven-tion further serves as an excellent sanitary food since it con- ^
tains nutritive elements indispensable to the human body, such as iodine or bromine. The seaweed powder helps to maintain the human body in alkaline condikion. The seaweed powder of the present invention may thus be used simply as flour food or in combination with other food for enhancing nutrition. The seaweed powder may be utilized in preparing a stock by adding it to water. `~
According to the present invention, as the oxygen pro-duced from hydrogen peroxide or hydrogen peroxide compound will facilitate the stripping-off of the skins of seaweed, algin can be prepared in an extremely simplified process, not requiring such complicated steps as in the con,ventional method described ~
above. Particularly, the present invention is of advantage in `
that because of the bleaching function of the active (atomic~
oxygen produced from hydrogen peroxide or hydrogen peroxide com-pound, no decoloring or bleaching step is needed. This is in contrast with the conventional method which indispensable includes a decoloring or oxidizing bleaching step with such agents as active carbon or o~her oxidizing agents. ~ -The method of the present invention can be applied to all ~orts of seaweeds (phaeophyceae or brown algae, chlorophyceae ` .:

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or green algae, and rhodophyceae or red algae~, being particularly suitable for application to Laminaria japania ARESCHOUG, yiant Kelp macrocystis pyrifera, Sargassum horneri C. AGAROH, Sargassum micracanthum YENDO and Undaria pinnatifida SURINGAR. -In the practice of the present invention where hydrogen peroxide or hydrogen peroxide compound is added to seaweed which - has been pretreated in a suitable manner, the hydrogen peroxide per se or hydrogen peroxide porduced from the hydrogen peroxide cornpound will penetrate through the outer skin of the seaweed or, when the seaweed is cu~ into sections, along between the outer and inner skins of the seaweed into the inner parts of the seaweed and is there decomposed to produce molecular or atomic oxygen due to the function of an enzyme such as catalase, which is present mainly between the inner skin and outer skin of the seaweed.
The oxygen gas expands or loosens the outer skin to strip the - same of the seaweed, while preventing hydrogen peroxide, hydrogen peroxide compound or oxygen from further penetrating into the inner parts of the seaweed.
;~ The rate of stripping-off of the outer skin depends firstly on the permeability of the outer skin to hydrogen peroxide or hydrogen peroxide compound and secondly on the looseness of the outer skin. The more easily the outer skin lets hydrogen peroxide and hydrogen peroxide compound permeate therethrough and the looser is the outer skin, the more rapidly the swelling of the seaweed will proceed so as to cause the stripping-off of the outer skin thereof.
In stripping-off the outer skin of seaweed according to the present invention, the function of catalase or ot~er enzyme present in the seaweed is influenced by various operational i factors such as the concentration o hydrogen peroxide, pH of the treating li~uid, temperature, reaction time, etc.
From the view point of operational ease and time re-- 5 ~
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10~3104 quired, hydrogen peroxide or hydrogen peroxide compound is pre-ferably added to the seaweed in an amount ranging 3 - 20%
calculated as an aqueous solution of hydrogen peroxide. When ~;
the concentration of aqueous solution of hydroyen peroxide is lower than 1%, the operation time becomes so long as to be un~
suitable for practical purposes. On the other hand, adding of hydrogen peroxide or hydrogen peroxide compound in an amount ex- ' ceeding 20% of aqueous solution of hydrogen peroxide does not give any significant additional effect.
The step for stxipping-off the outer skin of seaweed in the present invention is suitably carried out in the temperature range of from 30 to 80C. ~ lower temeperature, for example, 20C, will render the reaction too slow to be unsuitable for practical purposes. On the contrary, the employment of a higher temperature entails the disadvantage that the hydrogen peroxide or hydrogen '~ -~
peroxide compound undergoes excessive gasification which leads to troubles in operation and thus re~uired complex countermeasures.
Operation at a temperature higher than 80C is further undesirable since it causes substantial change in the chemical structure of `
seaweed.
It should be further mentioned that the outer skin stripping proces.s of the present invention can be carried out not only by simple addition of hydrogen peroxide or hydrogen peroxide compound (pH: neutral or weak acidic) but also, if desired, by addition of a suitable alkali or acid in combination with the hydrogen peroxide or hydrogen peroxide compound.
For example, such acid as sulfuric acid, hydrochloric acid, acetic acid or acetic anhydride may be added along with hydrogen peroxide or hydrogen peroxide compound. In the low pH
region caused by addition of such an acid, loss of algin by dis-solution is advantageously lessened although the rate of de-composition of hydrogen peroxide and hence the rate of the strip-~63~

ping of the outside skin from the seaweed are retarded. However, - for practical operation, the operation is preferably conducted in a pH value higher than 4 since excessively low pH adversely re-tards the decomposition of hydrogen peroxide. In a case where an organic acid is added together with hydro~en perox~de, a peracid will form from the two compounds (for example, peracetic acid will be formed from acetic acid and hydrogen peroxide~, and the peracid will then produce hydrogen peroxide in the aqueous solution.
In a case where the stripping-off of the outside skin of seaweed is carried out in an alkaline region by adding alkali ~;
such as sodium carbonate, ammonium carbonate or aqueous ammonia along with hydrogen peroxide or hydrogen peroxide compound, the rate of decomposition of hydrogen peroxide is accelerated result-ing in increased rate of the stripping-off of the outside skin.
However, since excessive addition of alkali quickens the loss of alginic acid by dissolution and further necessitates troublesome . , .
subsequent steps, in practical operation the stripping-off process ~ , is preferably conducted in a pH range of less than 8.
It should be further added that the process for strip-ping-off the outside skin of seaweed may preferably be carried out together with ultraviolet or sunbeam irradiation. as the decomposition of hydrogen peroxide or hydrogen peroxide compound "
due to enzyme (catalase etc.) is activated and accelerated.
According to the method of the pres0nt invention, the outer skin stripped off of the body of -the seaweed floats up to the upper portion of the liquid with the oxygen bubbles while the body (meat) of the seaweed per se settles toward the bottom of the liquid, thus the floating outer skins can be easily removed from the system by overflow of water. Remaining hydrogen peroxide, acid and alkali are removed by continued washing with water. The body of the seaweed is dryed and powdered into seaweed powder as desired. It is added that the outer skin per se may be separately powdered ~or utilization for perfume since it has the so-called "scent of seaweeds". ~ ~
In preparing algin from seaweed according to the method ' .
of the present invention, the body of the seaweed, the seaweed which has been stripped of its outer skin in the way described above is alkaline treated with alkali, alkali metal salt or al- `
kaline earth metal salt to extract alginic acid as algin there-from. The most suitable alkali, alkali metal salt and alkaline earth metal salt for use in the alkali extraction of the present invention includes Na2C03, (NH4)2C03, or NH40~. Other salts such as NaOH, ~a2S03, Na3P04, Ca(OH)2, CaC03, etc, may also be used, The ~ollowing is an example of the alginic acid extrac-tion step of the pre,sent invention: to 100 y of the white body oE seaweed is added 2 - 3 liter of 1% N~I40H aqueous solution with stirring to obtain a viscous solution. The solution is then fil-tered with filtering cloth. When diluted hydrochloric acid is -stepwise added to the filtrate obtained, alginic acid is congelated into agar-like product containing a large amount of water therein which then float up in the liquid. ~he floated product is then filtered and added with a small amount of alcohol. To the resultant filter cake is added 1% NH40H aqueous solution to form a colorless, transparent solution which is thereafter congelated with hydro-chloric acid. The congelated product is then pressed for remov- ~ ~
ing water oontained therein. If necessary, to the solid product ;~ ~-obtained is added 96% ethanol and the mixture obtained is heated . .
for a period of 2 - 3 hours, cooled and filtered. The filter ~`
residue is added with 10 cc of 1% hydrochloric acid solution (prepared by adding 80% alcohol to hydrochloric acid), and heated at 80C for 20 minutes for removing the remaining metal salts bound to alginic acid and obtaining the final product. The yield of alginic acid obtained is 32 gram. When it is desired to con-,:
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vert alginic acid into ~ alginate, another step follows wherein,for example, 1 gram of alginic acid is added with about 56 cc of alkali, alkali metal salt or alkaline earth metal salt.
Without any troublesome pretreatment as re~uired in the conventional methods, the present invention thus provides an extremely simplified method ~or preparing algin from seaweed since the extraction of alginic acid is conducted after the outer skin of the seaweed is stripped off by the function of hydrogen per-oxide.
To further illustrate the present invention, but not to limit the same, the following examples are given.
Example 1 ..
To 2.50 g of dried Laminaria were added 10 times by volume of water and 10 cc of acetic acid. The mixture thus ob-tained was added with stirring with 4.8 g of 35~O H202 aqueous solution resulting in 5.6% ~22 aqueous solution. The reaction `
was carried out at 30C under pH 5.3. After elapse of 5 minutes -from the initiation of the stirring, violent evolution of bubbles was observed, indicating the initiation of the reaction by the decomposition of H202 by the function of the enzyme (catalase etc.).
The violent evolution of bubbles continued by further progress of the stirring, and eventually the stripping-off of the `~
outer skin of the seaweed occurred. The meat of the seaweed was whit~ and transparent, while the outer skin stripped-off retained ~
its original color (brownish dark blue). The operation was main- , tained for 2 hours and then the outer skin stripped-off was re-` moved by overflow of water. The body (meat) of the seaweed was -sufficiently washed with water and dried to obtain 2.488 g of ;
dried seaweed powder.
Example 2 ;~ , ` To 2.572 g of dried Undaria pinnatifida (wakame seaweed) were added 10 times by volume of water and 10 cc of aqueous _ g _ , ~
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1~63i()4 ammonia. The mixture thus obtained was added with 4.2 g of 35% H202 aqueous solutlon to obtain 5% H202 a~ueous solution.
The reaction was carried out at 30C under pH 8, in the sa.ne manner as in Example 1, resulting in the stripping-off of the outer skin of the seaweed. The meat of the seaweed was white, while the outer skin stripped-off retained its original color.
- After the operation was maintained for 2 hours, the outer skin stripped-off was removed by overflow of water. The meat of the seaweed was washed with water and dried to obtain 2.571 g of dried seaweed powder. '~
Example 3 To 4.339 g of dried Sargassum micracanthum C. AGAROH
were added 10 times by volume of water and 13 cc o~ 35% H202 aqueous solution resuLting in 8% H202 aqueous solution of neutral pH. The reaction was carried out at 30C in the same manner as in Examples above. After elapse of 4 hours when the evolution ter-minated, the outer skin was removed while the meat was washed with water and dried to obtain 4.308 g of dried white seaweed powder.
; 20 Exam~le 4 To 4.541 g of dried Sargassum horneri C. AGAROH was added ten times by volume of water and 4 g of Na2C03. The mixture thus obtained was added with 32.5 g of 35% H202 aqueous solution resulting in 14.6% H202 aqueous solution. As the reaction was conducted at 35C under pH 8 and further under ultraviolet ray irradiation, violent evolution of bubbles was observed as in the ~ ;
exarnples above and eventually the seaweed was stripped of its outer skin. The meat of the seaweed was found to be white. After ;

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elapse of 4 hours from the initiation of the reaction, the outer skin stripped was removed and the meat of the seaweed was washed with water and dried to obtain 4.533 g of white dried seaweed powder.

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E~ample 5 100 g o dried Vlopteryx pinnatifida was sufficiently washed with water, added with 0.5% hydrochloric acid, allowed to stand at room temperature for a period of 2 hours, and then washed again with water to remove the hydrochloric acid.
To the mixture thus obtalned was added hydrogen peroxide compound CH3C(=O)OOH, which had been prepared by the reaction of ;
hydrogen peroxide with glacial acetic acid in a conventional manner. The addition was stepwise as solid state or as dilute aqueous solution (e.g. 10% aqueous solution) so that the resulting concentration of hydrogen peroxide was 5% to the total of the mixture and the pH was adjusted to be 5.
On initiating the stirring of the mixture after comple-tion of the addition of the hydrogen peroxide compound, the de-composition of peracetic acid started to produce hydrogen per-oxide as expressed by the following equation~
,:
CH3C(C=O)OOH + H20 = CH3COOH + H202 Hydrogen peroxide was decomposed by the function of catalase or other enzyme to evolve bubbles caused thereby. In about 4 hours from the initiation of the evolution of b~tbbles, the seaweed was completely stripped of its outer skin to yield white meat of seaweed, while the stripped skin floated ~Ip in the liquid. After stirring the mixture for further 2 hours, the stripped outer skin was removed by overflow of water along with remaining hydrogen peroxide, the acid and the salt.
The white meat of the seaweed (the seaweed which had been stripped of its outer skin) thus prepared was dried to obtain 98 g of white seaweed powder.
Example 6 The operation as did in Example 5 was repeated except that solid hydrogen peroxide compound which had been prepared by the reaction of H202 with lime was added, per se or in an aqueous , . ~ , ~ ,. , , - . . . .. . . .

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solution, along with addition of suitable mineral acid, organic acid NaHC03, Na2C03, NH40H, (NH4)2 3 4 3 weed in place of the compound CH3C(=O)OOH to obtain seaweed powder.
Example 7 , . . .
100 g of dried Ulopteryx pinnatifida was sufficiently washed with water, added with 0.5% hydrochloric acid, allowed to stand at room temperature for a period ~f 2 hours, and then washed again with water to remove the hydrochloric acid.
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; 10 To the mixture thus obtained was added hydrogen peroxide compound CH3C(=O)OOH, which had been prepared by the reaction of . , hydrogen peroxide with glacial acetic acid in a conventional manner. The addition was stepwise as solid state or as dilute aqueous solution (e.g. 10% aqueous solution) so that the resulting concentration of hydrogen peroxide was 5% to the total of the ~ ;
mixture and the pH was adjusted to be 5.
On initiating the stirring of the mixture after comple-tion of the addition of the hydrogen peroxide compound, the de-composition of peracetic acid started to produce hydrogen peroxide as expressed by the following equation:

CH3C(C-O)OOH + H20 = CEI3COOH ~ H20 Hydrogen peroxide was decomposed by the function of catalase or other enzyme to evolve bubbles caused thereby. In about 4 hours from the initiation of the evolution of bubbles, the seaweed was completely stripped of its outer skin to yield , white meat of seaweed, while the stripped skin floated up in the liquid. After stirring the mixture for further 2 hours, the stripped outer skin was removed by overflow of water along with ;~
remaining hydrogen peroxide, the acid and the salt. ,~
:; ., -The white meat of the seaweed, that is, the seaweed --` which had been stripped off its outer skin in the manner above, ~ was immersed in about 100 cc of water. To the mixture was added ., .
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2 liter of 1% aqueous ammonia solution. The aqueous solution of ammonium alginate thus obtained was then filtered and press- ~;
dehydrated~ To the resulting filter resiclue was added 50 cc of 96% alcohol and the mixture thus obtained was heated for about 1 hour. The resultant was filtered and dried over sulfuric acid in vacuo to obtain about 38 g of alginic acid. The aqueous solution of said alginic acid is acidic (pH is 3.0 at 28C), does not reduce Fehling~s solution, produces furfurol and car-bonic acid when boiled with 12% HCl and exhibits a clear naph-toresorcinol reaction, The specific rotary power of the alginic acid was [~22 = _(3),5 Example 8 100 g of dried Laminaria Japonica was sampled, suffi-ciently washed with water to remove sand and salt attached there-to, and added with 0.5% ~ICl. The mixture obtained was allowed to stand at room temperature to cause sufficient swelling, and was then washed with water to remove the acid component. The mixture was added with about 300 cc of 10% aqueous ammonia to adjust its pH to 9 and further added with 225 cc of 3S% H202 aqueous solution to make the H202 concentration in the liquid 15%, On initiating bubbling, mild stirring of the liquid mixture was started and continued for about ~ hours~ The mixture was then allowed to stand for 2 hours, and removed of the outer skin which had been stripped off and of the excessive H202 remaining. When the meat of the seaweed thus obtalned was added with 10% ~a2C03 to adjust the pH to 8 and the mixture was stirred, the white meat of the seaweed was dissolved to produce trans-parent, viscous solution.
The solution was added with 1% HCl (in 80% alcohol solution) and heated at 80C for 30 minutes for removing the ': :
remaining salts bonded with alginic acid. (In this stage, the . ' .

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alginic acid is too resistant -to acid to be subjected to hydro-lysis and does not reduce Fehling's solution.) The alginic acid thus obtained, after being filtered and pressed, was heated twice in 80% alcohol and once in 96%
alcohol, eaeh heating being continued for one hour. The alginie acid was thereafter dried in a desiccator~ The yield of the alginic acid was 37g.
Example 9 The hydrogen peroxide compound in Example 8 was re-placed with the compound Na2C03 ~ 1.5H202 or the compound K2C03~2H202~0.5H20. (These compounds were prepared by reacting ~ `
1 mole of hydrogen peroxide with 1 mole of potassium carbonate or sodium carbonate at low temperature. The evmpounds are ehemically stable in dried state but are deeomposed to produce H202 gradually in a state o~ neutral aqueous solution and rapidly in a state of acidic aqueous solution.) ; The same operation was followed as in Example 8 to obtain 2 g of alginie acid.
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Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for preparing seaweed powder which comprises adding hydrogen peroxide or hydrogen peroxide compound to sea-weed to strip off the outer skin of the seaweed and then drying the seaweed which has been stripped of its outer skin.

2. The method according to claim 1 in which alkali is added to the seaweed in combination with the hydrogen peroxide or hydrogen peroxide compound.

3. The method according to claim 1 in which acid is added to the seaweed in combination with the hydrogen peroxide or hydrogen peroxide compound.

4. A method for preparing algin which comprises adding hydrogen peroxide or hydrogen peroxide compound to seaweed to strip off the outer skin of the seaweed and then alkaline-treating the seaweed which has been stripped of its outer skin to extract alginic acid therefrom.

5. The method according to claim 4 in which alkali is added to the seaweed in combination with the hydrogen peroxide or hydrogen peroxide compound.

6. The method according to claim 4 in which acid is added to the seaweed in combination with the hydrogen peroxide or hydrogen peroxide compound.