Institute of Medicine Food and Nutrition Board Committee on Food Chemicals Codex

Revised Monograph - Konjac Flour

Please send comments to the Committee on Food Chemicals Codex, National Academy of Sciences, FO 3042, 2101 Constitution Avenue, N.W., Washington, DC 20418 or email them to [email protected]. All comments must be received by December 15, 1996, for consideration for the First Supplement. ______

June 13, 1996

Konjac Flour

Konjac; Konnyaku; Konjac Gum; Yam Flour

CAS: [37220-17-0] DESCRIPTION

A hydrocolloidal polysaccharide obtained from the tubers of various species of Amorphophallus. Konjac Flour is a high molecular weight, nonionic glucomannan primarily consisting of mannose and glucose at a respective molar ratio of approximately 1.6:1.0. It is a slightly branched polysaccharide connected by b-1,4 linkages and has an average molecular weight of 200,000 to 2,000,000 daltons. Acetyl groups along the glucomannan backbone contribute to solubility properties and are located, on average, every 9 to 19 sugar units. The typical powder is cream to light tan in color. Konjac Flour is dispersible in hot or cold water and forms a highly viscous solution with a pH between 4.0 and 7.0. Solubility is increased by heat and mechanical agitation. Addition of mild alkali to the solution results in the formation of a heat-stable gel that resists melting, even under extended heating conditions.

Functional Use in Foods Gelling agent; thickener; film former; emulsifier; stabilizer.

REQUIREMENTS

Identification A. Microscopic Test Stain about 0.1 g of the sample with 0.01% methylene blue powder in 50% isopropyl alcohol, and observe microscopically. Konjac Flour may be identified by the presence of flattened elliptical particles, which are generally 100 to 500 mm in length along the long axis. Unground Konjac Flour is clearly distinguished from other hydrocolloids by the presence of saclike cells that contain glucomannan. The surface of these cells has a reticulated structure. Particles of Konjac Flour are also birefringent under polarized light. These visual characteristics may remain even if the sample is finely ground, but are less pronounced. B. Gel Test At room temperature, add 5 mL of a 4% sodium borate solution to a 1% solution of the sample in a test tube, and shake vigorously. If Konjac Flour is present, a gel forms. (Konjac Flour solutions gel in the presence of sodium borate, similar in reaction to that of other galactomannans such as guar gum and locust bean gum.) The Heat-Stable Gel Test, below, distinguishes Konjac Flour from guar and locust bean gums. C. Heat-Stable Gel Test Prepare a 2% solution of the sample by heating it in a boiling water bath for 30 min with continuous agitation and then cooling the solution to room temperature. For each g of the sample used to prepare the 2% solution, add 1 mL of 10% potassium carbonate solution to the fully hydrated sample at ambient temperature. Heat the mixture in a water bath to 85°, and hold quiescently for 2 h without agitation. Konjac Flour 1 forms a thermally stable gel under these conditions. Related hydrocolloids such as guar gum and locust bean gum do not form thermally stable gels and are negative by this test. Arsenic (as As) Not more than 3 mg/kg. Ash (Total) Not more than 5.0%. Carbohydrate (Total) Not less than 75.0%. Heavy Metals Not more than 10 mg/kg. Lead Not more than 5 mg/kg. Loss on Drying Not more than 15.0%. Protein Not more than 8.0%.

TESTS

Arsenic A Sample Solution prepared as directed for organic compounds meets the requirements of the Arsenic Test, Appendix IIIB. Ash (Total) Determine as directed in the general method, Appendix IIC. Carbohydrate (Total) The remainder, after subtracting from 100% the sum of the percentages of Ash, Loss on Drying, and Protein, represents the percentage of carbohydrates (glucomannans) in the sample. Heavy Metals Prepare and test a 2-g sample as directed in Method II under the Heavy Metals Test, Appendix IIIB, using 20 mg of lead ion (Pb) in the control (Solution A). Lead A 2-g sample prepared as directed for organic compounds meets the requirements of the Lead Limit Test, Appendix IIIB, using 10 mg of lead ion (Pb) in the control. Loss on Drying, Appendix IIC Dry at 105° for 5 h. Protein Transfer about 3.5 g, accurately weighed, into a 500-mL Kjeldahl flask, and proceed as directed under Nitrogen Determination, Appendix IIIC. Percent protein equals percent N ´ 5.7.

Packaging and Storage Store cool and dry in a closed container away from direct heat and sunlight.

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