*3.11. XRD*

The XRD result of lyophilized royal jelly powder with 0.5% and without trehalose were plotted in Figure 7. It could be observed that the TR 5 sample and control sample showed similar particularly sharp diffraction peaks at 22.32◦ and 23.74◦. It was proven that the addition of trehalose did not change the crystal structure of the lyophilized royal jelly powder obviously and all the samples had a complete crystal state. The vibration intensity of the diffraction peak reflected the degree of crystallization of the substance. Compared with the control group, the strength of the diffraction peak of the lyophilized royal jelly powder with trehalose was significantly enhanced. The crystallinity of the lyophilized royal jelly powder with trehalose was changed, which could lead to the enhancement of the vibration intensity of the characteristic peak.

**Figure 6.** The DSC result of the control sample and royal jelly lyophilized powder with 0.5% addition of trehalose (TR 5).

**Figure 7.** X-ray diffraction result of the control sample and royal jelly lyophilized powder with 0.5% addition of trehalose (TR 5).

### *3.12. FTIR*

The FTIR spectrum obtained from 4000 to 400 cm−<sup>1</sup> was employed to represent the lyophilized powder of royal jelly. As shown in Figure 8, the band at 3426 cm−<sup>1</sup> was identified as the vibration of the –OH of carbohydrates, water, and organic acids [53]. The peak of all samples at 2936 cm−<sup>1</sup> was attributed to C–H stretching in carboxylic acid and NH3 stretching in free amino acids. The most important information used to distinguish the sample was in the 1800–750 cm−<sup>1</sup> region. The absorption peaks at 1643, 1527, 1338 and 1238 cm−<sup>1</sup> represented the of the protamine group [54]. High specific for amino acids and proteins were the peaks near 1338 cm−<sup>1</sup> and the peak at 1045 cm−<sup>1</sup> corresponded to the C–O stretch of the carbohydrates [55]. The FTIR spectral graph showed that the chemical component of the lyophilized royal jelly with trehalose had no change.

**Figure 8.** X-ray diffraction patterns of the control sample and royal jelly lyophilized powder with 0.5% addition of trehalose (TR 5).

### **4. Conclusions**

Herein, a novel method combining trehalose and royal jelly is successfully developed to enhance the free radical scavenging ability and the nutrition stability of royal jelly lyophilized powder after the VFD process. With systematic analysis, 0.5 wt.% of trehalose is selected as the best addition content which can reduce the loss of TFC and TPC during fabrication and exhibit the best DPPH radical scavenging ability as well as the lowest hygroscopicity. TFC and TPC contents of the powder increase obviously from 1.71 to 2.08 mgGAE·g−<sup>1</sup> and 7.4 to 11.2 mgRE·g−1, respectively. Moreover, the bulk density and tapped density increase from 0.353 to 0.432 g·mL−<sup>1</sup> and from 0.592 to 0.668 g·mL−1, respectively, which enhance conducive to the storage, processing, and transportation of lyophilized powder. The addition of trehalose can also improve the solubility of lyophilized powder and reduce the hygroscopic property and water activity of powder, which are the key factors to the flowability and of stability the lyophilized powder. According to the FTIR and XRD results, the chemical composition and crystal structure of the lyophilized royal jelly powder have no obvious change. The DSC result shows that trehalose can improve the stability of royal jelly lyophilized powder.

**Author Contributions:** Investigation, Methodology, Formal analysis, Writing—original draft, L.L.; Formal analysis, Visualization, Writing—review and editing, P.W.; Data curation, Methodology, Investigation, Y.X.; Project administration, Supervision, Conceptualization X.W.; Project administration, Supervision, Data curation, Funding acquisition, X.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Science and Technology Key Projects of Jilin Provincial Department of Science and Technology in 2019 (20200402069NC), "The key technology of vacuum freeze drying of royal jelly of northeast black bee and the development of convenient and nutritious food industrialization".

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data are contained within the current manuscript.

**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### **References**

