Thesis (Ph.D.)--Chulalongkorn University, 2013

The goal of this research is to devise a new processing method for production of purified konjac glucomannan (KGM) flour from corms of Buk Nuea Sai (Amorphophallus muelleri). The research on production of KGM flour from konjac corms was divided into following four parts: selection of the most appropriate anti-browning agent and soaking time for browning control of sliced corms; investigation the wet extraction process by using anti-swelling agent to improve glucomannan extraction and to study the effects of anti-swelling agent on physical and chemical properties of KGM flour; study of effects of different drying methods including hot air drying, multistage hot air drying, freeze drying, and microwave-vacuum drying on physical, chemical, and structural properties of KGM flour; and selection and optimisation of the most appropriate drying method for production of purified KGM flour for application in konjac industry. The results showed that using sodium metabisulphite as an anti-browning agent at 500 ppm with a soaking time of 10 min, was the most effective agent to retard browning reaction in konjac slices with low residual sulphite content as a requirement. In comparison, using sodium chloride at 10,000 ppm with a soaking time of 20 min, showed a performance comparable to sodium metabisulphite. In extraction process, using ethanol could provide higher extraction yield than sodium tetraborate. Meanwhile the whiteness index value and viscosity of konjac samples extracted with sodium tetraborate were higher than those extracted with ethanol. However, 50% ethanol was the most suitable anti-swelling agent for using in KGM extraction in case for safe consumption. After extraction process, the results showed that drying technique is the main factor that influences to the several important properties of KGM flour such as color change, bulk density, particle density, porosity, viscosity, morphology and sulphur dioxide residue. However, drying methods, drying temperature and drying time in this experiment did not affect the glucomannan content and FTIR spectra of KGM flour. The main factors that affect the glucomannan content of the KGM flour is the extraction medium and extraction technique. In order to meet the criteria of good quality KGM flour, the following factor are needed: the higher whiteness index of KGM flour can be obtained when the product temperature is above 60 °C in order to inactivate PPO activity for control the browning of KGM flour; choose the drying method in which provided low density and high porosity to promote the water absorption and viscosity of KGM flour; and thermal drying process and vacuum system can reduce the sulphur dioxide residue content in KGM flour. Using microwave vacuum drying at power level of 1440W for 7.5 min is an alternative drying method for KGM flour industry.