*2.1. Sample Collection*

The two methods are applied to the planting of "Huping" jujube. The rain shelter was built in the immature period of jujube fruit. The top is covered with plastic film, and the surrounding is ventilated. The full-maturity "Huping" jujubes cultivated in the open field and the rain shelter were collected from an orchard in Taigu, China, respectively. On the same day of collection, samples were transported to the laboratory, cleaned, and placed for four hours to return to room temperature. In this study, a total of 300 intact samples (150 rain-shelter samples and 150 open-field samples) were selected. For each cultivation, the KS algorithm [32] was used to divide the data set into a calibration set (114 samples) and a prediction set (36 samples) with a ratio of 3:1.
