D-Galactose (CAS 59-23-4, C₆H₁₂O₆, MW 180.16 g/mol) is an essential aldohexose monosaccharide — the C4 epimer of D-glucose — that differs from glucose by a single stereochemical inversion at carbon 4 (axial -OH at C4 in galactose vs equatorial in glucose). This seemingly minor structural change confers fundamentally different biological specificity. Galactose is metabolized via the Leloir pathway — a three-enzyme sequence named after Nobel laureate Luis Federico Leloir: (1) Galactokinase (GALK) phosphorylates galactose to galactose-1-phosphate using ATP; (2) Galactose-1-phosphate uridylyltransferase (GALT) transfers UMP from UDP-glucose to galactose-1-phosphate, yielding UDP-galactose and glucose-1-phosphate; (3) UDP-galactose 4-epimerase (UGE/GALE) interconverts UDP-galactose and UDP-glucose, feeding glucose-1-phosphate into glycolysis (net yield: 2 ATP per galactose). The Leloir pathway is not merely a catabolic route — it is the essential gateway connecting galactose to two fundamental biological functions: cellular energy metabolism (glycolysis) and glycoconjugate biosynthesis (UDP-galactose as the activated glycosyl donor for galactosyltransferase reactions). UDP-galactose is the obligatory substrate for: lactose biosynthesis (galactose + glucose β1→4, the primary carbohydrate in human breast milk), galactocerebroside biosynthesis (GalCer — the major glycolipid of the myelin sheath in brain and nerve tissue), and glycoprotein galactosylation (terminal Gal-β1→4-GlcNAc LacNAc epitopes on N-linked and O-linked glycans essential for protein folding, immune recognition, and cell adhesion). In red algae, L-galactose derivatives form the repeating disaccharide units of agar and carrageenan — billion-dollar polysaccharide industries. UPOR Biotech supplies ≥99% HPLC D-galactose with full USP/EP/JP compliance for all applications.

D-Galactose serves as a critical ingredient across four major sectors: (1) Cell Culture Media — galactose at 1-10 g/L in chemically defined media for biopharmaceutical production (CHO, HEK293, hybridoma). As galactose is metabolized more slowly via the Leloir pathway than glucose via glycolysis, galactose-based media reduces lactate accumulation — the primary cause of culture acidification and reduced productivity — enabling higher peak cell densities, prolonged viability, and improved recombinant protein yields. Galactose supplementation also enhances glycoprotein galactosylation by providing the UDP-galactose pool required for proper N-glycan processing, terminal galactose capping, and sialylation — directly impacting therapeutic protein half-life and immunogenicity. (2) Pharmaceutical Excipient — D-galactose USP/EP/JP grade serves as a filler, diluent, and sweetener in oral solid dosage forms, chewable tablets, and effervescent formulations. GRAS status and low sweetness (30-40% of sucrose) make it ideal for pediatric and geriatric formulations. (3) Infant Formula & Nutrition — galactose is an essential structural component of lactose (galactose + glucose β1→4), the primary carbohydrate in human breast milk (~7%). Galactose is critical for neonatal brain development as the obligate precursor for galactocerebroside biosynthesis (myelin sheath glycolipid). Preterm and term infant formulas supplemented with lactose support neurodevelopment and gut microbiota maturation. (4) Cosmetics & Personal Care — D-galactose functions as a natural humectant (moisture-attracting) and prebiotic in skincare, supporting a healthy skin microbiome and providing gentle moisturization without the stickiness of glycerol. OEM and private label formulations available from UPOR Biotech with flexible MOQ starting at 1 kg.

D-Galactose and D-glucose are C4 epimers — aldohexose monosaccharides with the identical molecular formula (C₆H₁₂O₆) and molecular weight (180.16 g/mol) that differ by the stereochemical configuration at only one chiral center: carbon 4. In the stable chair conformation, D-glucose has the C4 hydroxyl group in the equatorial position (pointing outward), while D-galactose has the C4 hydroxyl in the axial position (pointing upward). This single stereochemical inversion produces far-reaching biochemical consequences: (1) Metabolism — glucose enters glycolysis directly at glucose-6-phosphate (via hexokinase, Km ~0.1 mM); galactose must first traverse the three-enzyme Leloir pathway before entering at glucose-1-phosphate, resulting in slower, more regulated metabolic flux and reduced lactate production — the key advantage for cell culture media. (2) Biosynthesis — the axial C4 -OH in galactose is the molecular signature recognized by galactosyltransferases that add galactose from UDP-galactose to growing glycan chains; glucose (equatorial C4 -OH) is not recognized — galactose cannot be substituted by glucose for glycoprotein galactosylation, galactocerebroside biosynthesis, or lactose production. (3) Cell Recognition — galectins (a family of 15 mammalian lectins) specifically recognize β-galactoside epitopes; the axial C4 -OH is essential for galectin binding — glucose does not bind. Galectins regulate cell adhesion, apoptosis, immune response, and cancer metastasis. (4) Disease — galactosemia (GALT deficiency) is a severe inborn error of metabolism because galactose cannot be metabolized through glucose pathways; galactitol accumulates and causes cataracts, liver failure, and neurotoxicity. There is no analogous “glucosemia.” (5) Sweetness — galactose is approximately 30-40% as sweet as sucrose (vs 70-80% for glucose), making it less sweet and less cariogenic. (6) Marine polysaccharides — L-galactose derivatives (from epimerization at C5 in red algae) form agar and carrageenan — glucose does not form analogous gel-forming polysaccharides. The C4 epimer distinction is a defining principle of carbohydrate biology: one hydroxyl orientation at one carbon of a six-carbon sugar redirects metabolism, biosynthesis, recognition, disease susceptibility, and industrial utility.

Galactosemia is an autosomal recessive inborn error of metabolism caused by deficiency in one of the three Leloir pathway enzymes — most commonly galactose-1-phosphate uridylyltransferase (GALT), causing classic galactosemia (incidence ~1:30,000-60,000 live births). When GALT is deficient, galactose-1-phosphate accumulates intracellularly, and excess galactose is shunted into the polyol pathway: aldose reductase converts galactose to galactitol (dulcitol), a sugar alcohol that cannot cross cell membranes and accumulates osmotically in tissues — causing catastrophic organ damage. The clinical manifestations are multi-system and severe: Ocular — galactitol accumulation in the lens causes osmotic swelling, denaturation of lens crystallins, and irreversible cataract formation within the first weeks of life if untreated; bilateral “oil droplet” cataracts are a classic finding. Hepatic — galactose-1-phosphate toxicity in hepatocytes causes hepatomegaly, jaundice (unconjugated hyperbilirubinemia progressing to conjugated), cirrhosis, and liver failure. Neurologic — galactitol accumulation in the brain contributes to cerebral edema, intellectual disability, speech deficits (verbal dyspraxia), and motor dysfunction. Renal — galactosuria, aminoaciduria, proteinuria, and renal Fanconi syndrome from proximal tubular toxicity. Ovarian — hypergonadotropic hypogonadism and primary ovarian insufficiency in >80% of affected females, even with early dietary treatment. Newborn screening for galactosemia is mandatory in all 50 U.S. states and most developed countries — detected via elevated total galactose (>10 mg/dL) and reduced/absent GALT activity on dried blood spots (Guthrie cards) collected at 24-48 hours of life. Confirmatory testing includes quantitative GALT enzyme assay in erythrocytes, GALT gene sequencing (most common mutations: Q188R in European populations, S135L in African populations), and urine-reducing substances. Treatment is lifelong strict dietary galactose restriction: complete elimination of lactose (milk, dairy products, whey, casein) and galactose-containing foods from the neonatal period. Even with strict dietary compliance, long-term complications (cognitive deficits, speech disorders, ovarian failure, osteopenia) occur in a significant proportion of patients — likely from endogenous galactose production (UDP-glucose → UDP-galactose via GALE). Galactosemia underscores the absolute essentiality of the Leloir pathway: a single enzyme deficiency transforms an essential nutrient (galactose) into a systemic toxin (galactitol). UPOR Biotech D-galactose is labeled with full transparency — it is intended for pharmaceutical, cell culture, nutraceutical, and research applications, and is not for consumption by individuals with galactosemia. Safety documentation including MSDS and allergen statements is provided with every shipment.

Every shipment of D-Galactose ≥99% HPLC (Pharma/Food Grade) includes: COA (HPLC purity ≥99.0%, specific optical rotation [α]D²⁰ +78.5° to +81.5° for D-galactose, identity by IR spectrum matching USP D-Galactose reference standard, water content by Karl Fischer ≤1.0%, loss on drying ≤0.5%, residue on ignition ≤0.1%, chloride ≤0.005%, sulfate ≤0.005%, heavy metals ≤10 ppm with Pb ≤2 ppm / As ≤1 ppm / Hg ≤1 ppm / Cd ≤1 ppm, residual solvents per USP <467> / ICH Q3C, microbial panel per USP <61>/<62>, endotoxins ≤0.5 EU/mg per USP <85> where applicable, related substances — glucose ≤0.5%, lactose ≤0.1%, any single unknown impurity ≤0.1%, total impurities ≤1.0%), MSDS, HPLC Chromatogram (signed and dated), USP/EP/JP Compliance Statement, Certificate of Origin, BSE/TSE-Free Statement, Non-GMO Statement, Allergen Statement, HALAL Certificate, KOSHER Certificate, ISO 22000 + HACCP, ISO 9001:2015, FDA Facility Registration, Stability Data (25°C/60%RH real-time 36-month and 40°C/75%RH accelerated 6-month), Residual Solvent Declaration per ICH Q3C, Elemental Impurities Statement per USP <232> / ICH Q3D, and Complete Lot Traceability from raw whey lactose hydrolysis to finished D-galactose crystalline powder. Free sample (10-50 g) available for qualified B2B buyers. MOQ: 1 kg. All documents provided in English. OEM and private label services available with flexible MOQ and custom formulation support.