为制备可溶性丝素蛋白应用于食品，本文探讨了不溶性丝素蛋白向可溶性再生丝素蛋白转化的条件并分析丝素蛋白结构变化对其溶解性的影响。以丝素蛋白的溶解时间和再生丝素蛋白的氮溶解指数为指标分析了溶解体系、温度、盐浓度和乙醇浓度对丝素蛋白溶解的影响。研究表明，利用氯化钙-乙醇-水体系可将不溶性丝素蛋白溶解，当氯化钙在30%的乙醇溶液中浓度达到4 mol/L时，95 ℃保温9 min，丝素蛋白完全溶解，所得再生丝素蛋白氮溶解指数达到91%。利用低场核磁共振仪、圆二色谱仪、X-射线衍射仪和扫描电镜观测丝素在混合溶液中的结构变化，结果显示，在三元体系中，丝素与水结合逐渐增强，丝素纤维膨大，随后逐渐断裂为片层状，结晶结构破坏，再生丝素从β-折叠转变为无规则卷曲，导致溶解性改善。

Conditions for the transformation of insoluble silk fibroin into soluble regenerated silk fibroin and the effect of structural changes in silk fibroin on its solubility were examined to enable preparation of soluble silk fibroin for use in food products. The effects of solvent system, temperature, salt concentration, and ethanol concentration on the dissolution of silk fibroin, as assessed by dissolution time and the nitrogen solubility index of the regenerated silk fibroin, were analyzed. The results showed that insoluble silk fibroin could be dissolved in calcium chloride-ethanol-water systems; soaking of silk fibroin in a solution of 4 mol/L calcium chloride and 30% (V/V) ethanol and heating at 95 ℃for 9 min led to complete dissolution, and the nitrogen solubility index of the regenerated silk fibroin reached 91%. Structural changes in silk fibroin upon dissolution were also examined using low-field nuclear magnetic resonance (NMR) spectroscopy, circular dichroism spectroscopy, X-ray diffractometry, and scanning electron microscopy. In the calcium chloride-ethanol-water system, interactions between silk fibroin and water gradually increased in strength, the silk fibroin fibers swelled and gradually broke into a lamellar shape, and the crystal structure of the silk fibroin was destroyed. In solution, the structure of the regenerated silk fibroin changed from a β-sheet structure to a random coil structure, resulting in an improvement in solubility.

广西自然科学基金项目（2016JJE120003）