甘蔗原汁后混浊是指澄清甘蔗汁在贮存或商品流通期间发生成分变化，浊度增加或产生沉淀的现象。该研究通过聚丙烯酰胺凝胶电泳、组合式质谱鉴定、氨基酸组分分析和傅立叶红外分析等方法，研究甘蔗原汁后混浊物的基本成分、蛋白质的分子质量大小、种类、氨基酸组成及二级结构。实验发现，甘蔗原汁后混浊物中主要成分是总糖，其含量达60.94%，其次是灰分和蛋白质，含量分别为19.52%和18.43%，酚类仅为0.62%。后混浊蛋白质分子质量分布在42 ku左右和小于20 ku，分别鉴定出12种和44种蛋白，其中丰度较高的几种蛋白分别为protein Z，PREDICTED：calmodulin-7 isoform X1，PREDICTED：calcium-dependent protein kinase 34 isoformX1和hypothetical protein SORBIDRAFT_01g014740。后混浊蛋白质和上清液蛋白质的氨基酸组成差异不大，但在二级结构上差异明显。后混浊蛋白质中除了无规卷曲结构远高于上清蛋白质外，α-螺旋和β-转角分别比上清蛋白质低33.43%和22.42%，而β-折叠差异不大。总的来说，分子质量大小低于42 ku、疏水值高、α-螺旋含量低和无规卷曲含量高的蛋白质更容易参与甘蔗原汁后混浊。

Post-haze of raw sugarcane juice refers to the phenomenon that the clarified raw sugarcane juice undergoes changes in composition, increase of turbidity or precipitation during storage or commodity circulation. In this study, the basic composition as well as the molecular weight, type, amino acid composition and secondary structures of proteins of the sediment in sugarcane juice were studied by polyacrylamide gel electrophoresis, combined mass spectrometry, amino acid analysis and Fourier transform infrared spectroscopy. The experimental results showed that the main component in the sediment of the raw sugarcane juice was sugar (total sugar content 60.94%), followed by ash and protein (19.52% and 18.43%, respectively), and the content of total phenolics was only 0.62%. The molecular weight distribution of post-haze proteins was about 42 ku and lower than 20 ku, and 12 and 44 proteins were identified, respectively. Among them, the proteins with higher abundance are protein Z, PREDICTED: calmodulin-7 isoform X1, PREDICTED: calcium-dependent protein kinase 34 isoformX1, and hypothetical protein SORBIDRAFT_01g014740. The amino acid compositions of the post-haze proteins and the supernatant proteins were only marginally different, but their secondary structures differed significantly. Except that the content of random coil structure in the post-haze proteins was much higher than that of the supernatant protein, the α-helix and β-turn of post-haze proteins were lower than those of the supernatant protein by 33.43% and 22.42%, respectively, although the difference in the β-sheet was insignificant. In general, proteins with molecular weight slower than 42 ku, high hydrophobicity, low α-helix content and high random coil content more likely contributed to the post-haze of raw sugarcane juice.

国家现代农业产业技术体系资助（CARS-170502）；蔗糖产业省部共建协同创新中心；广西绿色制糖工程技术研究中心（2017GCZX）