*2.2. Spectrum Acquisition and SSC Determination*

Spectrum data were collected using an ASD Fieldspec3 spectrometer (analytical spectral device, Longmont, CO, USA) with spectral resolutions of 3 nm@350~1000 nm and 10 nm@1000~2500 nm and a spectral range of 350~2500 nm. The spectral curves of fresh jujubes cultivated in the open field and the rain shelter are shown in Figure 1. Although there were some differences in reflectance values of fresh jujubes between the two cultivation modes, the curve-change trends of the two cultivation methods were relatively similar. There were obvious absorption peaks related to the stretching vibration of O-H bond at the vicinity of 970 nm and 1400 nm. The signal-to-noise ratio was low, and the noise was loud at 350~450 nm and 2400~2500 nm. Therefore, the spectral information of 450~2400 nm was selected for subsequent analysis.

**Figure 1.** Mean spectrum of fresh jujubes. (**a**) Spectral curves of open-field cultivation, (**b**) spectral curves of rain-shelter cultivation, and (**c**) average spectrum.

The SSC of each sample was measured using a hand-held refractometer. The statistical values are shown in Table 1. The SSCs of fresh jujubes cultivated in the open field and rain shelter were 21.2–35.5% and 21.8–37.4%, respectively.


