Fig 1.
Flowchart of the saliva samples collected for the two main experimental groups: water (W) and apple juice (J) groups.
Fig 2.
Mean friction coefficient (µ) of hydrophobic surfaces in the presence of unstimulated whole-mouth saliva (uWMS), saliva after intervention with water [one-min intervention (SW1), and 10-min intervention (SW10)] as a function of entrainment speed.
Error bars represent standard deviations of three readings on pooled saliva (n = 32).
Fig 3.
Mean friction coefficient (µ) of hydrophobic surfaces in the presence of unstimulated whole-mouth saliva (uWMS), saliva after a one-min intervention with apple juice (SJ1), and saliva after a 10-min intervention with juice (SJ10), as a function of entrainment speed.
Error bars represent standard deviations of three readings on pooled saliva (n = 32 subjects).
Table 1.
Means and standard deviation (SD) of the friction coefficient (µ) of the five saliva samples in each boundary, mixed, and hydrodynamic regimes.
Fig 4.
Mean friction coefficient of hydrophobic surfaces (boundary regime) in the presence of unstimulated whole mouth saliva (uWMS), saliva after a one-min intervention with water (SW1), saliva after a 10-min intervention with water (SW10), saliva after a one-min intervention with juice (SJ1) and saliva after a 10 -min intervention with juice (SJ10), as a function of entrainment speed.
Error bars represent standard deviations of three readings on pooled saliva (n = 32 subjects). Figs 2–4 and Table 1 show that the friction coefficient (μ) of uWMS (0.011) was significantly lower (p < 0.05) than that of saliva after one min of intervention with either water (SW1: 0.112) or apple juice (SJ1: 0.045). uWMS, primarily derived from the submandibular and sublingual glands, is rich in mucins—heavily glycosylated proteins that retain water and form a hydrated biogel. This biogel containing mucinous proteins as well as cationic proteins contributes to boundary lubrication by preventing direct surface contact [5,18,19,44,45]. The observed boundary lubrication with uWMS in this study likely involved a salivary pellicle adsorbed onto one or both sliding surfaces, effectively reducing the coefficient of friction (µ).
Fig 5.
Frequency and dissipation shifts (5th overtone) as a function of time and calculated hydrated mass changes in response to buffer (B), saliva (S), apple juice (J), and saliva-juice mixture (SJ) on hydrophilic gold surfaces.
Adsorption characteristics in apple juice (a) refer to protocol 1 in methods, influence of apple juice on saliva (b) refer to protocol 2 in methods or ex-vivo adsorption measurements (c) refer to protocol 3 in methods. Corresponding viscoelastic changes (-∆D/∆f) are presented in ai, bi and ci and hydrated mass (mg/m²) calculated using 3rd, 5th, 7th and 11th overtones are presented in aii, bii and cii for the respective protocol. Means with error bars representing standard deviations of at least three readings (n = 3 x 1).
Fig 6.
Mean and interquartile range (IQR) of total protein concentration (TPC) using BCA analysis across five saliva groups (n = 20).
Identical letters denote significant differences (p < 0.05).
Fig 7.
Exemplar SDS-PAGE profile shows the protein expression of six salivary proteins across five saliva groups (uWMS, SW1, SW10, SJ1, and SJ10) from two participants.
A molecular weight ladder is displayed on the right-hand side for reference.
Fig 8.
Log10 protein expression levels of the six salivary proteins across five saliva groups (uWMS, SW1, SW10, SJ1, and SJ10), as determined by SDS-PAGE analysis.
Significant differences and corresponding p-values are provided.