Table 2.

The color changes in L*, a* and b* axes (expressed as ΔL, Δa, and Δb values) at each experimental time point (HAP 1–3, HSF)

Group	Experimental time point
	HAP 1	HAP 2	HAP 3	HSF
ΔL
10 wt% nano-HAP	2.30 (1.12)aA	2.70 (1.12)aA	2.76 (1.36)aA	2.09 (1.72)*
1 wt% nano-HAP	1.13 (0.73)bB	1.51 (1.20)bAB	1.78 (1.70)aA	1.30 (1.67)*
Without HAP	− 0.01 (0.42)bA	− 0.13 (0.68)cA	− 0.08 (0.73)bA	− 0.14 (0.87)
Water	0.01 (0.01)	0.01 (0.02)	0.00 (0.04)	0.00 (0.03)
Δa
10 wt% nano-HAP	− 0.21 (0.21)aA	− 0.75 (0.90)bB	− 0.95 (0.86)bB	− 0.82 (0.63)
1 wt% nano-HAP	0.05 (0.47)aA	− 0.20 (0.72)abA	− 0.31 (0.83)abA	− 0.25 (0.85)
Without HAP	0.05 (0.33)aA	0.09 (0.40)aA	0.12 (0.36)aA	0.12 (0.37)
Water	0.01 (0.02)	− 0.04 (0.04)	− 0.03 (0.06)	− 0.03 (0.05)
Δb
10 wt% nano-HAP	− 1.34 (0.64)bA	− 2.55 (1.84)bB	− 2.66 (1.90)cB	− 2.71 (1.86)
1 wt% nano-HAP	− 0.84 (0.63)abA	− 0.96 (0.83)aA	− 0.10 (0.83)bA	− 0.88 (0.94)
Without HAP	0.03 (0.47)aA	0.21 (0.96)aA	0.25 (0.96)aA	0.25 (0.93)
Water	0.00 (0.03)	− 0.01 (0.04)	0.02 (0.04)	0.01 (0.05)

Results are shown as mean value (standard deviation)

HAP 1: the first circle of nano-HAP application;

HAP 2: the second circle of nano-HAP application;

HAP 3: the third circle of nano-HAP application;

HSF: application of hydrodynamic shear force;

Lowercase letters indicate the differences between different groups at same experiment time point;

Capital letters indicate the differences of the same group between different experiment time points;

Different superscripts of individual letters indicate groups that statistically differed from any other group (P < 0.05);

Same superscripts suggest that groups showed no significant differences (P > 0.05);

From a (A) to c (C), the mean value is decreased;

* indicates the significant differences between HAP 3 and HSF (P < 0.05)