Shu Di Huang (Rehmannia glutinosa, prepared)

Shu Di Huang (prepared Rehmannia glutinosa) is a root-based traditional herb with the following documented composition: Iridoid glycosides are the primary bioactive compounds, with catalpol (an iridoid) present at approximately 0.1–0.5% in prepared forms (lower than raw due to steaming process). Oligosaccharides including stachyose, raffinose, and verbascose constitute approximately 15–25% of dry weight, contributing to prebiotic activity. Rehmanniosides A, B, C, and D are characteristic glycosides present at trace to low-percentage concentrations. 5-Hydroxymethylfurfural (5-HMF) forms during the steaming/wine preparation process and is present at approximately 0.05–0.3% dry weight, contributing to antioxidant activity. Amino acids are present at approximately 3–6% total dry weight, including arginine, glutamic acid, and alanine as predominant forms. Mannitol is present at approximately 1–3% dry weight. Minerals include iron (~15–25 mg/100g dry weight), zinc (~2–4 mg/100g), manganese (~1–3 mg/100g), potassium (~800–1200 mg/100g), calcium (~80–120 mg/100g), and magnesium (~40–80 mg/100g). Polysaccharides (Rehmannia polysaccharides, RPS) are present at approximately 3–8% dry weight and demonstrate immunomodulatory properties with moderate oral bioavailability (~20–40%). Vitamins are minimal; trace amounts of B-complex vitamins are present. Total carbohydrate content is high at approximately 60–75% dry weight due to sugars and polysaccharides. Fat content is negligible (<1%). Protein content is approximately 4–7% dry weight. Bioavailability note: Steaming with wine (the 'Shu' preparation) increases bioavailability of polysaccharides and reduces the cold properties of raw Rehmannia; catalpol content is reduced compared to Sheng Di Huang (raw form) but 5-HMF increases significantly, which may contribute to neuroprotective effects. Iridoid glycosides show limited oral bioavailability (~10–20%) but are subject to gut microbiome metabolism.