Konjac & Konjac Flour, Gum, and Glucomannan: Uses, Health benefitsKonjac Shirataki NoodlesTHICKENERS

Konjac gum and konjac glucomannan are two water-soluble hydrocolloids that can be used as a thickener, stabilizer, gelling agent, film former and fat replacer in food, with the European food additive number E425(i) and E425(ii), respectively.

The difference between these two ingredients is mainly the purity of glucomannan in them. Glucomannan is dietary fiber and the main functional component in konjac flour. This content is required ≥ 75% in konjac gum, while needed more than 95% in konjac glucomannan.

What is Konjac?
Konjac, a traditional agricultural food with a history of 1500 years in both China and Japan. It is the tuber (root) of the perennial plant of Amorphophallus konjac.

Moisture

Moisture has a great influence on the quality of dried konjac flour. Fresh konjac tubers have a high water content (80%-85%), so it is easily moldy, spoiled and cannot be stored for a long time.

Therefore, in order to prolong shelf life, the konjac is usually processed into dried slices or chips to reduce the water content (generally about 15%) after harvest.  

SO2
Konjac slices/chips are prone to browning during processing, so SO2 is often added to prevent browning and to make a bleaching effect.

That’s why you will see the item of SO2 content in the specification of both konjac gum and konjac glucomannan.

The dried konjac needs to be further processed into konjac flour to be used as food raw materials. The quality of the konjac flour primarily depends on the source of the konjac plant.

Components

The glucomannan is the main component in konjac tuber in a dry basis, the assay of which is about 30%-50%, and varies according to the types of konjac, and the rest are cellulose, starch, protein, soluble sugars, inorganic salts, alkaloids, vitamins and etc.

What is Konjac flour?
It is a general name for konjac powder, which can refer to both konjac gum and konjac glucomannan. Both konjac gum and konjac glucomannan (KGM) are derived from konjac flour.

Types of konjac flour
Konjac flour is made from the grinding of slices/chips of dried konjac. According to the purification of glucomannan, it can be classified into three types: common konjac flour, konjac gum and konjac glucomannan.

The color of konjac flour is an important item for judging the quality of konjac flour. The more white the color, the more the content of glucomannan in it.

1. Common konjac flour
Here means unpurified konjac flour and with the following properties:

Smell: with the inherent smell of konjac and a slight smell of sulfur dioxide.
Appearance: white, with a small amount of yellow, brown or black particles.
Purity: a very simple purification process to remove starch and cellulose.
Glucomannan content: not less than 65%.
Viscosity: ≥ 14,000 mpa.s
Mesh size: commonly with 40-120mesh and above 120mesh in the market.
2. Konjac gum

Also known as purified konjac flour, obtained by aqueous extraction of konjac flour. It is not claimed as dietary fiber and so without physiological benefits.

Smell: with the inherent smell of konjac.
Appearance: white to cream to light tan powder.
Glucomannan content: not less than 75%.
Viscosity: ≥ 23,000 mpa.s.
3. Konjac Glucomannan
Konjac glucomannan (KGM) is a natural food gum extracted from the hemicellulose component in the cell walls of Amorphophallus konjac. It is also a water-soluble dietary fiber.

KGM is a natural high-molecular-weight polysaccharide, with excellent hydrophilicity, gelability, emulsification, film-forming and thickening effect.

Due to these properties, KGM has a wide range of applications in food.

Manufacturing process


Glucomannan is produced by washing konjac flour with water-containing ethanol as it is easy to absorb water and insoluble in ethanol.

The ethanol precipitation manufacturing process is to isolate glucomannan by removing starches, cellulose, protein and other components. And follows centrifugation, milled, drying and other processes to obtain pure KGM.

Structure

Glucomannan is composed of D-mannose and D-glucose units at a molar ratio of 1.6:1.0, connected by b(1-4)-glycosidic bonds.

Structural formula of the repeating unit of konjac glucomannan
Chemical Structure of Repeating unit, Source

Specification
Other names   
Konnyaku
Yam flour
Konjac mannan
Elephant yam
CAS number    37220-17-0
Chemical formula    C24H42O21 (Glucomannan)
Molecular weight    200,000–2,000,000 (konjac gum) 

500,000–2,000,000 (konjac glucomannan)

Properties
Solubility
The large molecular weight lowers the solubility of konjac in water, but the presence of a large number of hydroxyl groups in the molecule enables it to absorb around 80-100 times a quantity of their own.

Viscosity
Highest viscosity

Konjac forms highly viscous solutions after swells and hydrates in water. The viscosity of 1g konjac diss