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Yam tuber mucilage as a candidate substance for saliva substitute: in vitro study of its viscosity and influences on lysozyme and peroxidase activities.

OBJECTIVE
To investigate the viscosity of yam tuber mucilage (YTM) and its effects on lysozyme and peroxidase activities in solution phase and on surface phase.


METHODS
Two kinds of YTM were extracted, one containing both protein and carbohydrate and the other containing mainly carbohydrate. Hen egg-white lysozyme and bovine lactoperoxidase were used as lysozyme and peroxidase sources, respectively. Viscosity was measured with a cone-and-plate digital viscometer. Lysozyme activity was determined using the turbidimetric method, and peroxidase activity was determined using the NbsSCN assay. Hydroxyapatite beads were used as a solid phase.


RESULTS
The viscosity values of YTM followed a pattern of a non-Newtonian fluid. The carbohydrate concentration affected the viscosity values at all shear rates, while the protein concentration affected the viscosity values at low shear rates. It could be suggested that YTM composed of 1.0 mg/ml protein and 1.0 mg/ml carbohydrate has viscosity values similar to those of unstimulated whole saliva at shear rates present at routine oral functions. Hydroxyapatite-adsorbed YTM significantly increased the adsorption and subsequent enzymatic activities of lysozyme, but not those of peroxidase.


CONCLUSIONS
Yam tuber mucilage has viscoelastic properties similar to those of human saliva and enhances the enzymatic activity of lysozyme on hydroxyapatite surfaces.