Characterization and Prebiotic Activity in Vitro of Hydrolyzed Glucomannan Extracted from Fresh Porang Tuber (Amorphophallus Oncophyllus)

The technology for direct extraction of porang glucomannan (PG) from fresh tubers offers a faster and simpler
process, yielding high-purity glucomannan. However, PG’s high viscosity and low solubility limit its use in the food,
pharmaceutical, and health industries. Enzymatic hydrolysis of PG has the potential to improve these characteristics and
enhance its prebiotic activity. This study aimed to examine the characteristics and prebiotic activity of porang
glucomannan hydrolysate (PGH) derived from glucomannan extracted directly from the fresh tubers. PG was hydrolyzed
under optimal conditions at 37.6 °C for 3 h, pH of 6.8, and an E/S of 0.8 % (w/w). Analysis of PGH included the degree
of polymerization (DP), molecular weight (MW), viscosity, and solubility. Changes in the morphology, molecular
structure, and composition of PGH were assessed through scanning electron microscopy (SEM), Fourier-transform
infrared spectroscopy (FTIR), and high-performance liquid chromatography (HPLC), respectively. Prebiotic activity
analysis was conducted by determining the prebiotic activity score in vitro. The results revealed that PGH was composed
of 58 % mannohexaose, 40 % mannotriose, and 2 % mannobiose. Notably, PGH exhibited reduced granule size and a porous surface. FTIR analysis indicated a structural change in the PGH molecule after hydrolysis. The DP of PG decreased
by 1000 times, and the MW decreased by 60 times, leading to a 700-fold reduction in the viscosity of PGH. In contrast,
the solubility of PGH increased threefold, attributed to the disruption of glycosidic and hydrogen bonds between and
within glucomannan molecules during hydrolysis. These modifications in PGH characteristics make it more readily
fermentable by several Lactobacilli and Bifidobacteria without stimulating the growth of E. coli, resulting in a positive prebiotic activity score. As a result, PGH shows promise as a source of prebiotics and can be utilized in beverage products to enrich their nutritional value, consequently producing functional food.