超高压预处理对桑葚热风干燥特性及品质变化的影响

Effect of Ultra-high Pressure Pretreatment on the Hot Air Drying Characteristics and Quality of Mulberries

摘要:

【目的】提高热风干燥桑葚的品质与干燥效率。【方法】采用不同压力（0~300 MPa）的超高压预处理桑葚，通过低场核磁共振（LF-NMR）、显微结构观察、细胞壁组分定量、活性成分测定及电子鼻主成分分析等方法，系统研究其对干燥特性、水分分布、细胞结构和活性成分的影响。【结果】150 MPa为关键压力阈值，该条件下自由水比例达到峰值（T₂₃峰面积占比47.3%），细胞壁-膜系统发生选择性破裂并形成贯通腔隙，孔隙率显著提高。纤维素质量分数随着压力的升高逐渐下降，达到250 MPa后趋于稳定（10.28 mg/g），原果胶持续降解（300 MPa时降至10.25 mg/g），可溶性果胶质量分数逐渐上升至11.81 mg/g（300 MPa），表明高压会诱导果胶降解，进而引起细胞壁结构的变化。超高压预处理使干燥时间缩短38.5%，活性成分保留率显著提高（黄酮质量分数1.01 mg/g，总酚质量分数0.32 mg/g）。电子鼻分析显示，300 MPa时风味变化最大。【结论】综合品质与干燥效率，150 MPa为最佳预处理条件，通过细胞结构重组、水分状态转化及细胞壁组分降解的协同作用优化干燥过程，为桑葚高值化加工提供理论依据。

Abstract:

[Objective]This study aimed to improve the quality and drying efficiency of hot air-dried mulberries.[Method]Mulberries were pretreated with different pressure levels (0~300 MPa). The effects on drying characteristics, water distribution, cellular structure, and active components were systematically investigated through low-field nuclear magnetic resonance (LF-NMR), microscopic structural observation, quantitative analysis of cell wall components, active compound determination, and principal component analysis of electronic nose data.[Result]The key pressure threshold was identified at 150 MPa. Under this condition, the free water ratio reached its peak (T₂₃ peak area accounted for 47.3%). Selective rupture of the cell wall-membrane system formed interconnected cavities, significantly increasing porosity. The mass fraction of cellulose gradually decreases as pressure increases, stabilizing at 250 MPa (10.28 mg/g). The protopectin kept degrading (down to 10.25 mg/g at 300 MPa), and that of soluble pectin gradually increased to 11.81 mg/g, indicating that pectin degradation induced by high pressure dominated structure changes in the cell wall. Ultra-high pressure pretreament resulted in a reduction of 38.5% in drying time and significantly improved the retention of active compounds (mass fraction of flavonoid: 1.01 mg/g; mass fraction of total phenols: 0.32 mg/g). Electronic nose analysis revealed the greatest flavor change occurred at 300 MPa.[Conclusion]Considering both quality and drying efficiency, 150 MPa was selected as the optimal pretreatment condition. It exerts the synergistic effects of cellular structural reorganization, water state transformation, and degradation of cell wall components in improving the drying process. This study provides a theoretical basis for the high-value processing of mulberries.