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. HIGHLIGHTS The hydrolysis of porang glucomannan (PG) altered its molecular structure and resulted in the formation of porang glucomannan hydrolysate (PGH) containing 58 % mannohexaose, 40 % mannotriose, and 2 % mannobiose. The degree of polymerization and molecular weight of PG decreased significantly by 1000 times and 60 times, respectively, leading to reduced viscosity and improved solubility of PGH. The changes in PGH characteristics due to hydrolysis made it more readily fermentable by various strains of Lactobacilli and Bifidobacteria, resulting in a positive prebiotic activity score. GRAPHICAL ABSTRACT