Extraction of glucomannan from porang (Amorphophallus muelleri Blume) with freeze-thaw cycles pre-treatment

Amorphophallus muelleri Blume tuber, which is called porang in Indonesia, is one of the biggest glucomannan sources next to the konjac tuber. Glucomannan is commonly produced by ethanol extraction technique. This study aimed to propose the freeze-thaw cycles (FTC) pre-treatments with two factors including freezing time and the number of cycles before the glucomannan extraction step and investigated the impact on the physicochemical and morphological properties of the extracted glucomannan. The obtained data were statistically tested by means of multivariate analysis of variance (MANOVA) and post-hoc Duncan tests at a significance level (P) of 0.05. The treated samples were statistically compared with the control sample (without FTC) by means of the Dunnett’s test. The result showed that FTC pre-treatments changed the morphology of glucomannan from smooth to become porous globes showing more fissures on its surface. Generally, the freezing time treatments affected the physicochemical properties of glucomannan except for its protein and calcium oxalate contents. The number of cycles did not significantly affect the protein, starch, and calcium oxalate contents. The Dunnett’s test results indicated that the ash, carbohydrate (glucomannan), and color of the glucomannan obtained by the FTC pre-treatments were significantly different from those of the control sample.