Extraction, Isolation and Structural Characterization of Coconut Residue Polysaccharides: Immunomodulatory Activity, Antioxidant Capacity, and Gastrointestinal Digestive Behavior

Coconut residue, an abundant agro-industrial by-product, represents a potential source of bioactive polysaccharides. In this study, crude polysaccharides (CP0) were extracted from coconut residue and sequentially purified by DEAE–Sepharose Fast Flow anion-exchange chromatography and Sepharose CL-6B gel-filtration chromatography, yielding two major fractions, CP1 and CP2. Structural characterization revealed galactose- and glucose-rich heteropolysaccharides with distinct molecular characteristics. CP0 exhibited a molecular weight of 369.2 kDa, while the purified fractions CP1 and CP2 had molecular weights of 455.8 and 72.6 kDa, respectively. All fractions contained high carbohydrate contents (96.7–97.7%) and low protein contents (2.30–2.90%). Among the fractions, CP2 exhibited the greatest in vitro radical-scavenging capacity in DPPH and ABTS assays and stimulated the highest NO production in RAW264.7 macrophages without reducing cell viability. Simulated gastrointestinal digestion of CP2 was associated with a progressive reduction in apparent molecular weight and slight changes in relative monosaccharide composition. Gastric- and intestinal-digested CP2 preparations generally exhibited greater in vitro radical-scavenging capacity than native CP2. Intestinal-digested CP2 also produced the highest NO response among the recovered preparations and was associated with increased expression of iNOS, TNF-α, IL-1β, and IL-6 and reduced IL-10 expression, indicating a predominantly pro-inflammatory macrophage response. These biological responses occurred concurrently with digestion-associated molecular changes; however, the present experimental design does not establish a direct causal structure–activity relationship. Overall, the findings provide new information on the physicochemical characteristics, gastrointestinal behavior, radical-scavenging capacity, and macrophage responses of purified coconut residue polysaccharides and support further investigation of CP2 for potential food-related applications and value-added utilization of coconut residue.