Isolation, characterization and emulsion stabilizing properties of polysaccharides form orchid roots (salep)

Polysaccharide extracts were isolated from ground salep (dried orchid root). These were studied in terms of their composition and their capacity to affect the rheology and stability of emulsions. Successive extractions yielded three separate extracts, namely HBSS (hot buffer soluble solids, extracted at 70 °C, pH = 5.2), CHSS (chelating agent soluble solids, extracted at 70 °C, pH = 5.2), and DASS (diluted alkali soluble solids, extracted at 0 °C). HBSS comprised of negatively charged macromolecular populations sizing approximately between 600 kDa–700 kDa (d ∼ 500 nm), one at 50 kDa (d ∼ 70 nm), and a third one at 12 kDa (d ∼ 20 nm). Upon addition into Tween 20-stabilized emulsions, HBSS caused flocculation and enhanced creaming at low concentrations (0.1%), while at higher concentrations (≥0.7%) it drastically reduced creaming due to the increase of the aqueous phase viscosity. CHSS extracts contained a negatively charged polysaccharide population of approximately 50 kDa (d ∼ 140 nm). DASS extracts contained only small molecules. Addition of CHSS or DASS extracts into Tween 20-stabilized emulsions did not affect the viscosity or the creaming stability of the emulsions. Flocculation was induced at 2% CHSS. This can be predicted by a simple depletion model. The above suggest that salep hydrocolloids are highly efficient thickeners that can be extracted in a one-step process.