*2.10. Color Measurements*

Color values (*L\**, lightness; *a\**, redness; and *b\**, yellowness) of lyophilized powder were measured using a colorimeter (Xinlian Creation Electronic Co. Ltd., Shanghai, China). A standard plate CX 2064 was used as standard (*L\** = 94.52, *a\** = −0.86, *b\** = 0.68). The Δ*E\** was calculated according to the following formula:

$$\begin{cases} \Delta E\* = \left(\Delta a^2 + \Delta b^2 + \Delta L^2\right)^{0.5} \\ \Delta a = a\* - a\*\_{\text{sample}} \\ \Delta b = b\* - b\*\_{\text{sample}} \\ \Delta L = L\* - L\*\_{\text{sample}} \end{cases} \tag{6}$$

where Δ*L\**, Δ*a\** and Δ*b\** are the differences between the *L\**, *a\**, and *b\** values of the treatment and those of standard samples, respectively.

### *2.11. Particle Size*

The particle size distribution of lyophilized powder was determined by a dry powder laser particle sizer (Mastersizer 2000, Malvern Panalytical GmbH, Kassel, Germany) at 25 ◦C. Before the measurement, all the samples were ground through a 100-mesh sieve.

### *2.12. Scanning Electron Microscopy (SEM)*

The microstructure of lyophilized powder without and with trehalose were analyzed by a scanning electron microscope (SEM) (ZEISS EVO 18, Zeiss, Oberkochen, Germany). The SEM images were captured using a voltage of 20 kV and a 1500× magnification or a 6000× magnification.
