Abstract:

The water composition in chestnut fruit plays an important role in physiological metabolism and quality changes. In this study, Chinese chestnuts (Castanea mollissima Blu.) from Wangmo County in Southwest Guizhou Province, China, were used as test material. Low-field nuclear magnetic resonance (NMR) technology was used to test the transverse relaxation decay signal of hydrogen nuclei in chestnut fruit with different moisture contents (48%, 38%, 28%, 18%). The SIRT model was used to obtain inversion data of the transverse relaxation time (T2). Nuclear magnetic resonance images (MRI) were obtained by spin echo (SE) imaging, while texture analysis and colorimetry were employed to assess textural and color attributes of the pulp, respectively. Results showed that natural water loss changed the binding state of water in chestnut fruit, leading to significant water migration and gradual weakening of free and immobile water signal amplitudes with increasing water loss. The total inversion peak area of chestnuts with different moisture content differed. With increasing water content, the NMR signal and peak area both increased, showing significant correlation. NMR imaging enabled direct visualization of water content in different stages based on light and dark imaging features. The chestnut flesh underwent calcification during natural storage, with hardened fruit texture, increased resistance to extrusion and chewing, and decreased cohesiveness and springiness (in the later stage). Adhesiveness exhibited an initial decrease, with no significant variation in the later stage. In the early stage of water loss, fruit pulp underwent oxidization, causing a gradual change to a dark red color. In the late stage of water loss, the chestnut fruit underwent severe calcification, and the pulp turned white with increased brightness. These results provide a reference for understanding the mechanism underlying moisture migration and product quality control in the processing of fresh C. mollissima fruit.

摘要：

板栗（Castanea mollissimaBlu.）果实中的水分组成在其生理代谢及品质变化过程中具有重要作用。本研究以贵州黔西南望谟县板栗为实验材料，利用低场核磁共振技术，对不同水分含量（48%、38%、28%、18%）的板栗果中氢核的横向弛豫衰减信号进行测试，并利用 SIRT 模型对数据进行反演，得出横向弛豫时间T2 的反演数据。采用自旋回波脉冲序列对板栗果的质子密度加权成像；使用物性测试仪分析质构特性，利用色差仪分析板栗失水过程中果肉颜色的变化。结果显示，自然失水改变了板栗果中水分的结合状态，水分发生明显迁移，自由水和不易流动水的信号幅值随失水程度的加剧而逐渐减弱。不同含水率板栗的反演峰总面积不同，随着含水率的增加，核磁共振信号增强，峰面积增大，两者具有显著的相关性。核磁共振成像技术通过图片明暗不同，可直观反映不同阶段的水分含量。板栗果实自然贮藏过程中发生石灰化，果实质地发生硬化，挤压咀嚼时抵抗力增大，失水初期内聚性和弹性变化不显著，后期下降；粘附性前期降低，但后期变化不明显；板栗失水初期果肉发生氧化，颜色逐渐呈暗红色，失水后期石灰化较为严重，果肉颜色变白，亮度增加。本研究结果可为板栗加工过程中的水分迁移机制探讨以及产品的品质控制提供参考。