Authors:
Dr. Le Ngoc Hung^*1, MSc. Mai Van Nam², MSc. Dai Thi Viet Lan³
1. Research and Technological Transfering Center - National Academy of Science in Vietnam
2. Hanoi University of Science Technology
3. DAIBIO Traditional Medicine Company

There are various technological processes globally for producing GM (glucomannan). The common process for producing low-quality GM powder (up to 58% glucomannan) uses a drying technology where konjac slices are dried at temperatures above 80°C in an SO₂ gas stream to prevent browning of the GM powder. The dried konjac slices are then ground, and the dry konjac peel powder is separated from the konjac powder using an air separator to obtain GM powder products【7】.

The production process for refined konjac powder usually involves first producing low-quality GM powder using the drying technology, followed by purification in a salt solution to prevent browning. This process removes starch, soluble sugars, proteins, minerals, and other impurities. The product is then precipitated with alcohol, dried, and refined into GM powder with a glucomannan content exceeding 80%【8, 9】.

Studies on the chemical properties, GM extraction【10】, and the development of konjac cultivation have also been conducted in Vietnam in recent years【11, 12, 13】. These projects used imported equipment, so their practical application has been limited【10】. In previous studies, we successfully developed an improved two-stage technological process (wet grinding/centrifugal separation followed by cold drying) to produce GM powder from high-GM-content konjac species commonly found in Vietnam. The improved two-stage process uses advanced wet grinding and cold drying technologies【2, 14, 15】. However, the production line we designed and manufactured is not yet complete or synchronized. Currently, there are no publications or practical applications in Vietnam for producing GM powder from Krausei konjac tubers using a domestically integrated production line with low costs and high applicability for widespread use【2】.

A cold-drying device was designed, manufactured, and used for the first time globally to dry konjac powder and konjac slices at a low temperature of 10°C. This technology has the advantage of preventing browning of moist konjac powder during long drying periods.

The cold-drying device operates optimally with a motor airspeed of 2,500 m³/hour, capable of removing 8 kg of water per hour at 10°C, with drying times of 10-12 hours. When using both drying chambers with 18 trays, the device achieves a capacity of 250-300 kg per batch. The moisture content of the final product meets the required level of less than 10%.

From this production line, we developed a pilot-scale processing technology for konjac powder products, technical-grade konjac powder, and refined konjac powder using 200 kg of fresh konjac tubers as input per batch.

Impact of ethanol concentration on the weight of refined GM powder products
Table 1: The effect of ethanol concentration on the weight of refined GM powder.

Ethanol concentration (%)	Weight of fresh Amorphophallus tubers	Weight of dry powder	Weight of refined GM product (g)	Refined GM content (%)	Efficiency (%)
70	750	163,30	91,83	80,00	12,24
80	750	164,30	93,07	81,83	12,40
90	750	165,30	94,27	83,10	12,57
96	750	164,00	99,07	84,00	13,21
99	750	164,00	99,77	84,30	13,30

In ethanol solutions with different GM concentrations ranging from 70% to 99%, hydrogels reach equilibrium when swelling, and water absorption reaches a critical value, which is the equilibrium water absorption.

Table 2: The effect of ethanol concentration on the swelling capacity of refined GM powder.

Ethanol concentration (%)	Water absorption of GM (g/g)	Specific surface area of ​​GM (m2/kg)
70	330,00	7.351,33
80	251,00	5.221,33
90	121,33	3.653,00
96	11,00	96,00
99	10,00	93,30

For the ethanol concentrations examined—99%, 96%, 90%, 80%, 70%—it was observed that as the concentration increased, the swelling capacity of refined GM powder decreased. At 70% ethanol concentration, the refined GM powder swelled the most, with water absorption reaching 330 (g/g) and a specific surface area of 7,351.33 (m²/kg). When the ethanol concentration increased to 80%, swelling decreased, with water absorption reaching 251 (g/g) and a specific surface area of 5,221.33 (m²/kg). At 90% ethanol concentration, swelling significantly reduced to 121.33 (g/g), and the specific surface area dropped to 3,653 (m²/kg).

At ethanol concentrations of 96% and 99%, the swelling of refined GM powder was minimal and nearly identical, with water absorption values of 11 and 10 (g/g), respectively, and specific surface areas of 96 and 93.3 (m²/kg). For lower concentrations, refined GM powder exhibited significant swelling, resulting in loss during purification, leading to low efficiency and a lower glucomannan content. At 96% or 99% concentrations, the impact of water in the solvent on efficiency and product quality was minimal. Therefore, to reduce costs and production prices, a 96% ethanol concentration is recommended for refining konjac powder.

The specific surface area of commercial GM powder imported from overseas ranges between 85 and 12,600 (m²/kg).

Table 3: Quality indicators for refined GM powder products.

Parameters	Refined GM	Refined GM (Standard NY/T494-2002, China)
Particle size (mesh)	91,6% on 120 mesh	Above 90,0% on 120 mesh
GM (% khô)	90,5%	Above 90%
Viscosity (mPals)	30.600	Above 30.000
Huminity (%)	7,4	Less than 10
Ash level (%)	1,7	Less than 3,0
Pb (mg/kg)	0,2	Less than 0,8
As (mg/kg)	0,2	Less than 3,0
SO2 (g/kg)	0,192	Less than 0,3
pH	5,9	5,0 - 7,0
Contamination CFU/g	Meets requirements	Less than 3.000
Odor	Characteristic smell	Konjac Characteristic

 

References

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