Lubrication behavior of ex-vivo salivary pellicle influenced by tannins, gallic acid and mannoproteins

Abstract

The objective of this study was to investigate the influence of tannins and gallic acid on the salivary lubrication behavior. Furthermore, the effects of pH and mannoproteins in combination with gallic acid on the lubrication of saliva were studied. The addition of gallic acid and tannins were found to increase friction caused by the removal of the saliva film. Tannins resulted in higher friction compared to gallic acid. Lowering pH increased friction of gallic acid mixtures with saliva, due to stronger interactions between gallic acid and saliva. The increased friction caused by gallic acid was inhibited by the addition of mannoproteins due to the hydrogen bond interactions between gallic acid and mannoproteins, thereby decreasing the complex formation between gallic acid and salivary proteins. A correlation of 0.96 was found between the hydrodynamic diameter of the aggregate and the delta friction suggesting that the formation of aggregates determined the lubrication behavior.

Keywords: Aggregate; Astringency; Diameter; Mouthfeel; Saliva; Tribology.

Figure 1

A schematic representation of the friction coefficient, μ, as a function of time obtained by the dynamic protocol. Saliva was added at time 0 of the measurement. After obtaining a constant baseline value as the result of saliva addition (AvCoF₁), the model solution (MS) was added after 300 s. The Av.CoF₂ was calculated using only the data points after stabilization of the interaction between saliva and MS stabilized.

Figure 2

Friction coefficient as a function of time for gallic acid (GA) (a) and tannins (T) (b) in demi-water solution at different concentrations mixed with human saliva in a 1:1 ratio. W refers to water, and S refers to saliva. The friction coefficients represent mean values based on five measurement points. (c) Δμ values as a function of saliva, gallic acid and tannins concentrations. Gallic acid (dotted bars) and tannins (striped bars) solutions were mixed with human saliva in a 1:1 ratio. The values are presented as a mean value ±standard error. The letters ^a-c in each bar identify that the samples are significantly different according to Tukey's HSD test: p < 0.05.

Figure 3

(a) Δμ values as a function of gallic acid concentration for gallic acid (GA) diluted in water (solid bars) and phosphate buffer (pH 3) (striped bars). All the solutions were added in the presence of ex vivo salivary film. (b) The hydrodynamic diameter of saliva–gallic acid aggregates in buffer (striped bar) and without buffer (dotted bars). The values are presented as a mean value ±standard error. The letters a–e in each bar identify that the samples are significantly different according to Tukey's HSD test: p < 0.05. (c) Δμ as a function of hydrodynamic diameter for gallic acid. The line is the best through the data points.

Figure 4

(a) Δμ values as function of gallic acid concentration for gallic acid (GA) (solid bars) and gallic acid plus mannoproteins (M) (striped bars). All the solutions were added in the presence of an ex vivo salivary film. (b) Hydrodynamic diameter of pure saliva (solid bar), saliva–gallic acid combinations (striped bars) against saliva–gallic acid–mannoproteins (dotted bars). All the solutions were diluted in pH 3. The values are presented as a mean value ±standard error. The letters a–e in each bar identify that the samples are significantly different according to Tukey's HSD test: p < 0.05.