Comprehensive structural analysis and immunostimulant activity of complex polysaccharides from dietary fibers of biribá (Annona mucosa) pulp, a tropical fruit from Amazon region.

Tropical fruits are an important and yet underexplored source of dietary fibers, and biribá (Annona mucosa), a fruit native to the Amazon region, remains poorly characterized in this regard. In this study, soluble (SDF) and insoluble dietary fiber (IDF) fractions from biribá fruit pulp were extracted, fractionated, and structurally characterized using a combination of enzymatic-gravimetric methods, chromatographic techniques, monosaccharide composition, linkage analysis, and NMR spectroscopy. Six distinct polysaccharides were identified. The SDF fraction yielded a highly methyl-esterified (DE = 68.67 ± 0.43%) homogalacturonan, a type II arabinogalactan (Mw of 62 kDa), and a highly branched 4-O-methyl-glucuronoxylan. The SDF fraction was evaluated as a macrophage modulator in vitro, and was non-cytotoxic at concentrations up to 1000 μg/mL, while stimulating macrophages to secrete nitric oxide, a classical marker of the M1 phenotype. The IDF fraction contained a low-substituted acidic xylan, a xyloglucan/mannan complex (Mw of 36 kDa) and a cellulosic residue. Overall, this study provides the first detailed characterization of biribá pulp polysaccharides, revealing marked structural diversity across dietary fiber fractions. The observed increase in nitric oxide production by macrophages provides initial evidence of the biological activity of the soluble dietary fiber fraction and supports further investigation of the relationship between its structural features and biological properties.