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.