Effect of Sodium Carbonate Pretreatment on Drying Characteristics and Cuticular Wax of Lycium barbarum L.

In this study, scanning electron microscopy (SEM) and gas chromatography-mass spectrometry (GC-MS) were employed to investigate the effects of Na₂CO₃ pretreatment on the drying time, cuticular wax micromorphology and wax composition of mature goji berries from four varieties (Ningqi 1, Ningqi 5, and two new lines: Z44 and A16) with significantly different drying characteristics. The results showed that the surface of goji berries was covered with neatly arranged, smooth band-shaped strips. After treatment with different concentrations of Na₂CO₃, the epicuticular wax partially dissolved, transforming the wax layer from a smooth film to a rough, net-like structure. The 1% Na₂CO₃ pretreatment shortened the drying time by an average of 10.32% compared with the untreated control, while 2.5% Na₂CO₃ reduced it by an average of 21.93% across different varieties. After Na₂CO₃ pretreatment, total cuticular wax content decreased significantly in all varieties compared with the control. Specifically, after 1% Na₂CO₃ treatment, total wax content decreased significantly in Ningqi 5 (from 499.64 to 304.67 mg/cm²) and Ningqi 1 but not significantly in Z44 and A16 compared with the control group. Following treatment with 2.5% Na₂CO₃, total wax content decreased significantly for all varieties, with Ningqi 5 showing the largest reduction from 499.64 to 270.21 μg/cm², and Ningqi 1 showing the smallest reduction from 492.53 to 404.05 μg/cm². Additionally, epicuticular and intracuticular wax exhibited similar trends, with significant decreases observed in the alkane and ester components of the wax. Correlation analysis indicated significant positive correlations between drying time and the contents of epicuticular and intracuticular wax, alkanes and esters, suggesting these as key factors affecting the drying efficiency. Furthermore, polysaccharide content remained stable, significant variety-dependent changes in flavonoid content were observed, and betaine content increased after Na₂CO₃ pretreatment. In summary, Na₂CO₃ pretreatment alters the microstructure of the cuticular wax of goji berries, reduces the wax content and the major components (e.g., alkanes), thereby affecting the hydrophobic barrier integrity, accelerating moisture loss and shortening the drying time.