Maca polysaccharides: structural diversity, biological activities, and structure–activity relationships

Maca (Lepidium meyenii Walp.) is a high-altitude cruciferous crop native to the Peruvian Andes. Its edible hypocotyl accumulates structurally diverse polysaccharides that exhibit a broad spectrum of bioactivities, including immunomodulatory, antioxidant, anti-fatigue, and hepatoprotective effects. This review systematically summarizes recent advances in the extraction, purification, and structural characterization of maca polysaccharides. Five major structural types have been identified: α-glucans, arabinogalactans (types I and II), homogalacturonans, rhamnogalacturonans, and mannose-containing heteropolysaccharides, with molecular weights spanning three orders of magnitude (3.0-1951.0 kDa). We critically analyze structure-activity relationships, demonstrating that biological functions are governed by the interplay of molecular weight, monosaccharide composition, glycosidic linkage patterns, and spatial conformation. Key findings reveal that medium-molecular-weight fractions (200.0-400.0 kDa) exhibit optimal immunomodulatory activity, specific monosaccharide motifs confer receptor selectivity, and triple-helix conformations enhance immune recognition. Current limitations-including structural heterogeneity, incomplete mechanistic understanding, and lack of clinical validation-are discussed, alongside future research priorities. This work provides a comprehensive framework for understanding maca polysaccharide structure-function relationships and guiding their future development as functional food ingredients.