Konjac glucomannan (KGM) Property
KGM is water-soluble dietary fiber and can be used as a gelling agent, thickener, stabilizer, emulsifier and film former.
KGM is readily dissolved in water and it can absorb 100-fold as much as water in volume. Its water solution is a pseudo-plastic liquid, characterized by shear thinning. One particle of konjac powder consists of extremely long thread-like macromolecules tangled together. When it comes in contact with water, water molecules enter and are absorbed into the chain, gradually causing the particle to swell to about 200 times as its original volume, and turning the konjac powder into viscous liquid.
KGM has the highest molecular weight and strongest viscosity among any dietary fiber known to science, and has extremely high density.
The unmodified naturally acetylated konjac glucomannan produce highly viscous solutions. Typically, 1% in water of commercially available konjac products has viscosities from at least 20.000cP to more than 40.000cP when measured at 30 oC, the highest than any other natural thickening agents.
KGM interacts synergistically with carrageenan, xanthan gum, locust bean gum (LBG) and starch. For example, the addition of 0.02-0.03% crude KGM to 1% xanthan gum will raise its viscosity by 2-3 times under heating. Konjac-xanthan gels are cohesive and extremely elastic in nature. Max. gel strength is seen at a ratio of konjac and xanthan between 1:2,5 to 1: 4.
The konjac-carrageenan interaction is similar to that of LBG-carrageenan apart from the konjac-carrageenan interaction being much stronger.
Konjac interacts with most starches to produce a remarkable increase in viscosity allowing for an optimization of starch-rich formulations, whether the purpose is a reduction of calories or improvement of texture.
Unlike xanthan gum, guar gum or locust bean gum, konjac gum is the non-ionic type and therefore little influenced by the salt in the system. At ambient temperature, konjac gum remains stable without precipitation even if the pH drops to a level below 3.3. When konjac gum is used instead of locust bean gum as the stabilizer and added to ice cream, cheese and other dairy products, it will stabilize their quality by preventing the development of ice crystals.
As a gelling agent, KGM is quite unique for its ability to form thermo-reversible and thermo- irreversible gels under different conditions.
In food industry, many kinds of products rely on the Gelling property of hydrophilic colloids to form their special shape or structure and to guarantee their timely thaw at a certain temperature. Carrageenan gum, pectin, gelatin and sodium alginate fall into this category.
Xanthan gum does not gelatinize when used alone, but it can form gel at any pH when used in combination with konjac gum. At a pH of 5, the two gums show a greatest synergistic effect and when xanthan gum is used with konjac gum at a ratio of 3:2, the greatest gelatification will be achieved. This gelatification of the compound gum behaves as heat reversible: it appears in the solid state under indoor temperature only if it is no higher than 40℃., it will be in a semi-solid or liquid state at 50℃ or above. When the temperature drops back to the ambient temperature, it will resume the solid state. Base on this property of the compound gum, various types of jelly, budding, jam and fat-free confectioneries can be made by adopting different concentrations of the compound gum and adjusting to different pH values.
KGM is composed of a repeating polysaccharide chain. With addition of a mild alkali such as calcium hydroxide, Konjac gel will set to a strong, elastic gel resisting melting even under extended heating conditions.
KGM solution does not form gel because its acetyl group prevents the long chains of glucomannan from approaching each other, However, it does form gel when heated at a pH of 9-10. This gel behaves stable to heat and it will remain stable under repeated heating at 100℃ or even at 200℃. In slight alkaline environment, konjac solution forms thermo-irreversible gel after cooling from hot solution. That is why this gel is called non-reversible gel, whose mechanism is that the acetyl deviates from glucomannan in a naked state when heated under an alkali condition and partial structural crystallization occurs due to the formation of hydrogen bonds between molecules. And KGM becomes stable due to the formation of a net-like structure with the crystals as nodes. Making use of the heat non-reversible property of the konjac gum, it has been widely used to make a great variety of foods, such as konjac cake, konjac chips, konjac slices, konjac noodles, and also imitating foods for vegetarians.
Konjac is a powerful film former - both alone and in combinations with other gums such as carrageenan.
Soluble Dietary Fiber Source:
The fresh konjac contains an average of 13% dry matter, 64% of the dry matter is glucomannan: 30% is starch.