WATER-SOLUBLE DIETARY FIBERS AND METHOD FOR PREPARATION OF SAME

Abstract: Dietary fibers having average molecular weight of 2,000 - 15,000, which are prepared by partially hydrolysing polysaccharides of Konnyaku powder with a cellulase derived from microorganisms belonging to the genous Aspergillus, which are readily soluble in water, which do not prevent adsorption of useful minerals such as calcium in the digestive tract, and which do not give rise to diarrhea when an excessive amount thereof is ingested.

Description: FIELD OF THE INVENTION The present invention relates to dietary fibers which are readily soluble in water, which do not prevent adsorption of useful minerals such as calcium in the digestive tract, and which do not give rise to diarrhea when an excessive amount thereof is ingested, and a method for preparation of same. The water-soluble dietary fibers in accordance with the present invention can be utilized as an additive to processed foods and drinkables. In other words, the water-soluble dietary fibers in accordance with the present invention can be utilized for preparation of processed foods and drinkables. BACKGROUND OF THE INVENTION Recently it has been indicated that there is a correlation between the decrease in the quantity of fibers ingested due to the tendency of increased uptake of highly refined foods and the increase of various symptoms or diseases such as constipation, irregularity of defecation, disturbance of intestinal flora, carcinoma of the colon, hypertension, diabetes mellitus and others. For this reason, it is recommended to take a much larger quantity of dietary fibers. Konnyaku is a kind of plant belonging to the family of Araceae (Amorphophallys konjac) and has been cultivated in Japan, China and other Asian.countries, Konnyaku powder is prepared by drying smashed tubers of Amorphophallus konjac. Konnyaku powder is sold in the market as the ingredient for a traditional food called Konnyaku (devil's tongue: a paste made from the polysaccharides prepared from tubers of Amorphophallus konjac). Konnyaku powder has been utilized as water soluble dietary fibers or as a material for the preparation of natural food of a low-calorie, since it contains glucomannan, in a high concentration up to about 80 % (by weight), which comprises water-soluble polysaccharides and is hardly digestible in the human digestive organs (cf. "Chemistry of polysaccharide" page 280, 1955, Kyohritsu Shupran Kabushiki Kaisha). More particularly, it has been reported that when Konnyaku is ingested, the dietary fibers thereof may reach to the large intestine without being subjected to digestion in the small intestine, and they are excreted. It has also been reported that cholesterol, derived from foods and bile, is absorbed in Konnyaku and coincidently excreted. Thus Konnyaku is effective to decrease the serum cholesterol level. Moreover, Konnyaku is effective to adjust intestinal functions or maintain good intestinal conditions and to manifest a growth promoting activity on Bifidobacteria (Kiriyama et al, Journal of Nutrition, Vol. 97, page 382, 1968; Mizutani et al, "Intestinal Flora and Nutrition", page 89, 1983, Gakukai Shuppan Center). Also it is reported that the dietary fibers in Konnyaku may swell in its aqueous solution to hold a surprinsingly huge quantity of water amounting to hundreds times of itself and that when the dietary fibers are ingested, they give rise to the perception of satiety since they reside for a prolonged period in the stomach and they reside for a short time in the intestine. Thus they are useful as a natural ingredient of a low-calorie food for the prevention from corpulence or obesity Innami et al, "dietary fibers", pages 73 and 76, 1982, Daiichi Shuppan) It is also required that oligosaccharide mainly in the range of disaccharides to hexasaccharides, which are prepared from hydrolysis of Konnyaku powder, are effective to promote growth of intestinal Bifidobacteria (Unexamined Patent Application Gazzette No.58-212780). PROBLEMS IN THE PRIOR ART Although Konnyaku powder has many useful effects as mentioned above, it has some deffects as follows: (1) During processing of an aqueous solution of Konnyaku powder, the solution tends to be highly viscous so as to form a gel. (2) The use of Konnyaku powder is rectricted due to its undesirable flavor and taste. (3) Konnyaku has a property of adsorbing minerals which are essential for human nutrition. Thus when Konnyaku powder is ingested along with other foods or a food containing Konnyaku powder is ingested, calcium is adsorbed to the Konnyaku in the foods. This may result in the obstruction of calcium absorption in the digestive tract or in a negative nutritional calcium balance which in turn results in the decrease in minerals in the bones so as to cause osteomalacia (Oku et al, Journal of Nutrition, Vol. 112, Page 410, 1982). According to the results of a study by the inventors, the osmotic pressure of 20 % aqueous solution of oligosaccharides, mainly comprising di- or trisaccharides (average molecular weight 400) which are obtained by hydrolysis of Konnyaku powder, is up to 500 m. Osm/kg H₂O which exceeds that of human body fluid which is 285 m Osm/kg H₂O. Aqueous solution of Konnyaku powder reach the large intestine retaining a large quantity of water which may result in symptoms of diarrhea. Therefore, it is required to restrict the dose of such oligosaccharides within a prescribed level. The inventors of the present invention have conducted a study on dietary fibers and found that an aqueous solution of partially hydrolysed Konnyaku powder has a relatively low osmotic pressure which does not cause diarrhea, and does not lead to a decrease in calcium content in the bones. The present invention is based on this discovery. SOLUTION OF THE PROBLEMS According to the method of the present invention, partially hydrolysed Konnyaku powder, having an average molecular weight of 2,000 - 15,000, can be prepared by suspending Konnyaku powder in water, then partially hydrolysing the polysaccharides included therein with a cellulase. The resulted products has various favorable functions referred to above while eliminating the defects of non-hydrolysed Konnyaku powder and exhaustively hydrolysed. PURPOSE OF THE INVENTION Therefore, it is an object of the present invention to provide dietary fibers which can be widely utilized in the food industry while retaining the favouable functions of intact dietary fibers of Konnyaku powder but eliminating the adverse effects thereof. More particularly, it is an object of the present invention to provide dietary fibers which can be widely utilized for the preparation of processed foods and which do not cause diarrhea due to its moderate osmotic pressure. It is another object of the present invention to provide a method for preparation of such water-soluble dietary fibers. DETAILED DESCRIPTION OF THE INVENTION Konnyaku powder, which can be utilized as the raw material in the present invention may be a fine powder, sieved powder to a medium particle size or a coarse powder. Konnyaku powder may be declorized and deodorized with alcohol. Glucomannan, isolated from pulverized Konnyaku tubers, is also utilized. Any enzymes, which may hydrolyze glucomannan, can be utilized in the present invention, for example, Cellulase derived from Aspergillus niger, Trichoderma viride and Penicillium notatum; mannanase derived from the genus of Streptomyces, Rhizopus niveus, Bacillus circulans and tuberous roots of Konnyaku. Among the enzymes which hydrolyse a β-glucoside bond in a molecule of glucomannan (endo-type), cellulases derived from microorganisms belonging to the genus of Aspergillus are preferable which hydrolyse endo-β-glycosidic linkage (endo-type). The reaction time and the pH of the enzymatic reaction may exert a large influence on the yield of the reaction products and molecular weights thereof. Most of the enzyme preparations available in the market are mixtures of exo-type enzyme such as exo-1,4-β-D-glucanase, endo-type enzyme such as endo-1,4-β-D-glucanase and β-glucosidase. Thus, it is necessary to determine the preferable reaction time, temperature and pH os as to perform the enzymatic reaction under conditions where the activity of exo-type enzyme is lowered to minimize the production of monosaccharides and oligosaccharides. For example, typical conditions for the enzymatic reaction will be 40 °C for 4 -16 hours or 55 °C for 4 hours as shown in examples 1 - 5. The resulting reaction products are heated to inactivate the enzymes; the supernatant liquid thereof is collected; the collected liquid is subjected to condensation with or without performing demineralization, decolorization and deodorization, and further subjected to drying to obtain powdery product of water-soluble dietary fibers. The dietary fibers in accordance with the present invention can be ingested as is or they can be added to various foods without changing the properties thereof. For example, they can be added not only to solid foods such as frozen desserts, breads and jelly but also to liquid foods or drinkables such as milk, and fruit juice. Some exemplified tests will be described hereinafter. Test 1 [Osmotic Pressure Test] (1) Materials Three kinds of 20 % aqueous solution of water-soluble dietary fibers having different average molecular weights (test samples), prepared in the same manner as stated in Examples 1, 2 and 4, and a 20 % aqueous solution of acid hydrolyzate (control sample), having average molecular weight of 400 obtained by hydrolysis of Konnyaku powder, were prepared to test. (2) Method Osmotic pressures of the test and the control samples were measured by the conventional method. (3) Results The results are shown in Table 1. The osmotic pressures of the test samples (water-soluble dietary fibers in accordance with the present invention) were lower than that of the control sample and that of human body fluid (285 m Osm/kg H₂O), and therefore ingestion of the dietary fibers in accordance with the present invention nevers causes diarrhea. Test 2 [Test to asses the effect on calcium deposit in the bones] (1) Materials The modified basic diet was used for feeding rats. The composition of the diet, used as the test diet in this test, was basically the same as that of the basic diet except that a portion of 20 % of corn starch was substituted with the corresponding quantity of the water-soluble dietary fibers (average molecular weight 15,000) prepared from commarcially available Konnyaku powder by the method set forth in Example 1 of the present invention. The composition of the control diet used in this test was basically the same as that of the basic diet except that a 20 % portion of corn starch in the basic diet was substituted with the intact Konnyaku powder without being subjected to hydrolysis. The details of the compositions of these diet feeds are shown in Table 2. (2) Method Three groups (A, B and C) of test animals each comprising 6 Wistar rats, were fed the three kinds of diet feeds respectively for 8 weeks then ash contents of the bones of the test animals were measured in accordance with the conventional method. The mean values and the standard deviations of the ash content (%) i.e the bones of the animals belonging to the respective groups were calculated in accordance with the conventional method. (3) Results The results are shown in Table 2. It was observed that the skeletal ash content of the animals was almost the same in group A (test feed) and B (basic feed), and that the ash content was lower in group C (control feed) compared with groups A and B. Skeletal ash content is directly proportional to calcium content thereof. It is perceived that addition of Konnyaku powder to feed decreases skeletal ash content while addition of the water-soluble dietary fibers in accordance with the present invention does not affect the skeletal ash content. Test 3 [Test relating to Diarrhea] (1) Materials An aqueous solution of water-soluble dietary fibers in a a concentration of 15 %, prepared in accordance with the method set forth in Example 4 (average molecular weight) 2,000), was used. (2) Method A One hundred gram portion of the aqueous solution (15 g of water-soluble dietary fibers) was administrated to 12 healthy adult subjects (22 - 50 years old, comprising 6 men and 6 women) for 7 days, and their stools were observed on the day following the last day of the period of administration. (3) Result The results are shown in Table 3. It was concluded that no-one alleged diarrhea and 90 % of persons had normal stools after uptake of the dietary fibers of the present invention for 7 days. Test 4 [Dietary Fiber Content] (1) Materials Samples 1, 2 and 3 of the dietary fibers, respectively prepared from commercially available Konnyaku powder in the same manner set forth in Examples 1, 2 and 4, and the intact Konnyaku powder were subjected to determination. (2) Method The dietary fiber content in the respective materials was measured by Prosky's method (Prosky et al, Journal of the Association of Official Analytical Chemistry, Vol. 67, page 1044, 1984). (3) Results The results are shown in Table 4. From Table 4, it is evident that the water-soluble dietary fibers in accordance with the present invention retain the characteristics of dietary fibers even after treatment to afford water solubility. Test 5 [Panel Test for Applicability to Frozen dessert] (1) Materials Having used the ingredients shown hereunder, frozen dessert was prepared in accordance with the conventional method. It should be noted that the test samples contained the water-soluble dietary fibers (average molecular weight 15,000) prepared in accordance with the method set forth in Example 1, while the control samples contained corn syrup instead of the water-soluble dietary fibers. (2) Method Three samples consisting of paired test samples and one control sample, or paired control samples and one test sample were given to each of 40 persons consisting of 20 women and 20 men. In order to assess the panel's reliability in perception each person is assigned to distinguish one odd sample in those uniform stimuli which are composed of two identical and one odd samples (triangle test). Each person is also instructed to declare one sample which they prefer most among the paired two and one odd samples (Paired-comparison test). Those who correctly distinguished the single distinct sample were eligible to be qualified panel members (Motosaburo Motoyama et al, "Application of stochastics to chemistry and biology" Vol.3, page 145, Nankohdoh, June 1961). (3) Results The results of the test are shown in Table 5. From the results shown in Table 5, the panels were recognized to be qua ified to distinguish the test samples from the control samples, and the number of those persons who preferred test samples and those who preferred control samples were almost the same. Test 6 [Panel Test for Applicability to Cookies] (1) Materials With the recipe shown hereunder, the test and the control samples of cookies were prepared. The test samples contained water-soluble dietary fibers (average molecular weight 7,000) prepared in the same manner as set forth in Example 2, and the dietary fibers were omitted in the control samples. (2) Method In the same manner as in Test 5, the Triangle test and the Paired-comparison test were conducted. (3) Results The results are shown in Table 6. From the results shown in Table 6, cookies of test samples were distinguishable from those of control samples, but substantial difference was not observed between the samples in Paired-comparison test. Test 7 [Applicability to Bread] (1) Materials With the recipe shown in the following table, bread for the test and the control samples was prepared. The test samples contained dietary fibers (average molecular weight 2,000), prepared in the same manner as in Example 4, and the control samples did not contain dietary fibers. (2) Method As in Test 5, Triangle test and Paired-comparison test were conducted with respect to the breads of test and control samples. (3) Results The results of the tests are shown in Table 7. Breads of the test sample was distinguishable from that of the control sample , but a substantial difference was not observed between the both samples in the Paired-comparison test. Test 8 [APPLICABILITY TO JUICE AND MILK] (1) Materials With the recipe shown in the following tables, the test and control samples of fruit juice and milk were respectively prepared. The test samples of fruit juice and milk respectively contained dietary fibers (average molecular weight 15,000) prepared in the same manner as in Example 1, and the control samples thereof did not contain dietary fibers. (2) Method As in Test 5, Triangle test and Paired-comparison test was conducted with respect to the fruit juice and milk of the test and the control samples. (3) Results No precipitation was observed in all the samples of both of fruit juice and milk. The results of the panel tests are shown in Tables 8 (for fruit juice) and 9 (for milk). The test samples of fruit juice and milk were distinguishable from those of the control samples, but substantial differences were not observed between the both samples in the Paired-comparison test. Example 1 To 80 ℓ of phosphate buffer solution (pH: 6.5), 67 g of cellulase A (trade name, purchased from Amano Seiyaku, Co., Ltd. JAPAN, specific activity: 15,000 U/g), derived from the microorganisms belonging to the genus of Aspergillus was added. The resulted mixture was heated to 40 °C, and 4.0 kg of commercially available Konnyaku powder was added thereto and agitated to form a solution. The resulting solution was allowed to stand at 40 °C for 4 hours to effect enzymatic hydrolysis, then the hydrolysed solution was heated to 100 °C for 10 minutes to stop the enzymatic reaction. The resultant mixture was subjected to centrifugation at 6,000 G, and the supernatant fraction was collected. The collected supernatant was successively passed through cation exchange resin column to the volume of 1,000 mℓ (Dowex 50 Wx8; H⁺type) and anion exchange resin column (Dowex 1x8; OH⁻ type) to the volume of 4,000 mℓ for demineralization. The demineralized reaction mixture was condensed and subsequently spray dried to obtain about 1,250 g of dried dietary fibers. The average molecular weight of the dietary fibers was 15,000. Example 2 Soluble fibers, in a quantity of 2,250 g, were obtained in the same manner as described in Example 1, except that enzymatic reaction was carried out for 8 hours. The average molecular weight of the dietary fibers was 7, 000. Example 3 Soluble dietary fibers, in a quantity of 2,650 g, were obtained in.the same manner as described in Example 1, except that enzymatic reaction was carried out for 12 hours. The average molecular weight of the soluble dietary fibers was 3,000. Example 4 Soluble dietary fibers, in a quantity of 2,800 g, were obtained in the same manner as described in Example 1, except that enzymatic reaction was carried out for 16 hours. The average molecular weight of the dietary fibers was 2,000. Example 5 To 30 ℓ of acetate buffer solution (pH: 5.3), 13 g of cellulase Nagase (trade name, purchased from Nagase BioChemical Industry Co., Ltd., JAPAN, specific activity: 1,000 U/g), derived from the microorganisms belonging to the genus of Aspergillus was added. The resulted mixture was heated to 55 °C, and about 1.33 kg of commercially available Konnyaku powder was added thereto and agitated to dissolve. In the same manner as in Example 1, except that the resulted solution was kept at 55 °C for 1 hours, about 740 g of dietary fibers were obtained. The average molecular weight of the dietary fibers was 5,000. SIGNIFICANCE OF THE INVENTION The significance of the invention is as follows: 1 ○ The water-soluble dietary fibers of the present invention retain the desirable effect of the conventional dietary fibers such as cholesterol adsorbability, whilst being soluble in water which is favorable for application in the food industry. 2 ○ The water-soluble dietary fibers of the present invention do not obstruct of useful minerals such as calcium in the digestive tract. 3 ○ The water-soluble dietary fibers of the present invention cause a relatively low osmotic pressure, and do not give rise to diarrhea even if an excess amount-thereof is ingested. 4 ○ The water-soluble dietary fibers of the present invention can be added to various types of foods and drinkables without affecting organoleptic characteristics thereof.

Claims: Dietary fibers comprising the partial hydrolysate of polysaccharides of Konnyaku powder having an average molecular weight ranging from 2,000 to 15,000 and the property of water solubility. A method for the preparation of water-soluble dietary fibers comprising: dispersing Konnyaku powder in water; partially hydrolysing polysaccharides of said Konnyaku powder with a cellulase which is derived from microorganisms belonging to the genus Aspergillus; and separating water-soluble dietary fibers having an average molecular weight ranging from 2,000 - 15,000 from the reaction mixture. Use of dietary fibers comprising the partial hydrolysate of polysaccharides of Konnyaku powder having an average molecular weight ranging from 2,000 to 15,000 and the property of water solubility in a method of preparing dietary products for treatment of medical conditions arising from absence of fiber in the diet.

Inventors: FUKUWATARI, YASUO, MIZOTA, TERUHIKO, NANBA, KAZUYOSHI, ONO, JOJI, TOMITA, MAMORU
Applicants: MORINAGA MILK INDUSTRY CO., LTD.
Application year: 1990
Main classification: A23L1
IPC codes: A23L1, C12P19, A21D2, C08B37, C12R1