Locust bean gum (LBG), also known as carob gum, is a galactomannan polysaccharide extracted from the endosperm of Ceratonia siliqua (carob tree) seeds, prized for its synergistic gelling properties and heat stability.
Molecular Structure
LBG features a linear backbone of β-(1→4)-D-mannopyranose residues with single α-(1→6)-D-galactopyranose side chains attached every 3.1–3.9 mannose units (galactose:mannose ratio ≈ 1:4), yielding high molecular weight polymers (0.3–2.0 × 106 Da) with minimal branching variability across cultivars. X-ray analysis reveals an extended ribbon-like solid-state conformation transitioning to semi-flexible coils in solution, with amorphous powder morphology.
Extraction and Properties
Endosperm (approximately 42% of kernel) milling, roasting (to inactivate enzymes), flaking, and alcohol extraction yield a white-to-off-white powder (pH 5.4–7.0, moisture content < 14%). LBG hydrates slowly in cold water (< 1% solubility at 25 °C) but disperses fully when heated (> 80 °C), forming non-gelling viscous sols convertible to borate-induced gels. It exhibits high thermal stability, salt tolerance, and shear-thinning rheology, with intrinsic viscosity reflecting extended chain dimensions.
Biomedical and Pharmaceutical Applications
LBG's biocompatibility supports its use in controlled-release matrices and mucoadhesive formulations. It stabilizes protein suspensions and can act as a prebiotic via selective fermentation, although limited clinical data currently constrain definitive therapeutic claims.