Physicochemical Properties and Glucomannan Content of Konjac Powder Obtained from Different Drying and Extraction Methods of Nuea-Sai Konjac Corms (Amorphophallus muelleri)

Abstract

Nuea-Sai konjac corm contains glucomannan, which is a water-soluble hydrocolloid, forming increasing viscous and gelling properties. Glucomannan is a dietary fiber that does not provide energy, it is therefore commonly used as a thickening agent and food ingredient in the health food industry. This research aimed to investigate the physicochemical properties and glucomannan content of konjac powder obtained from different drying methods, i.e. hot air drying at 60+2^oC, and solar drying, and extraction methods, i.e. mechanical particle technique; KPM, and ethanol extraction; KPE. The results showed that konjac powder obtained from hot air dryer konjac and extracted by KPE; KPETD, had the highest glucomannan content of 87.46±0.77% with no difference from commercial konjac content at 85%. It contained high moisture content, pH, redness (a*), and yellowness (b*) values, and had moderate lightness (L*). It also had higher peaks and final viscosity levels than the other samples. Whereas the sample obtained from hot air dryer by KPM; KPMTD, showed the highest level of L*, and oxalate content, but had the lowest values of a* and b*. The sample obtained from solar dryer by KPM; KPMSD, had the lowest glucomannan and final viscosity. While, the sample extracted by KPE; KPESD, showed a high b* and peak viscosity, but it had low moisture and oxalate contents. It also found that all konjac samples had higher peak viscosity than the commercial sample.