*甜菜红碱键会随着β-折叠的增加改变大豆分离蛋白原纤维的结构；
*大豆分离蛋白原纤维对甜菜红碱的结合力比大豆分离蛋白强；
*大豆分离蛋白原纤维对甜菜红碱的热保护作用比大豆分离蛋白强。
甜菜红碱（Betalain）是一种具有生物活性的水溶性含氮色素。然而，它们对热降解的敏感性限制了它们在食品加工中的应用。
上海交通大学农业与生物学院，上海食品安全工程技术研究中心的Hui-Shuang Zhao、Zhen Ma、Pu Jing采用多种显微镜和光谱技术研究了甜菜红碱与大豆分离蛋白原纤维（soy protein isolate fibrils，SPI-F）的相互作用，并对其热处理后的热稳定性进行了评价。AFM和TEM图像表明，甜菜红碱与SPI-F的配合物为小的无定形聚集体。荧光光谱显示SPI-F通过疏水作用与甜菜红碱结合。圆二色谱结果表明，SPI-F的二级结构随甜菜红碱键（合）而改变，α-螺旋（7.5%~6.9%）、β-转角（13.1%~12.9%）和无规卷曲（41.1%~40.7%）减少，β-折叠（38.3%~39.5%）增加。
SPI-F的加入降低了甜菜红碱的失色率，增加了热保留率，由55.3%提高到75.9%。这些结果表明SPI-F对甜菜红碱的热稳定性有保护作用，有利于其作为天然着色剂的广泛应用。
Interaction of soy protein isolate fibrils with betalain from red beetroots: Morphology, spectroscopic characteristics and thermal stability
Hui-Shuang Zhao， Zhen Ma，Pu Jing
Shanghai Food Safety and Engineering Technology Research Center, Bor S. Luh Food Safety Research Center, Key Lab of Urban Agriculture (South), School of Agriculture & Biology, Shanghai Jiao Tong University, Shanghai 200240, China
Abstract
Betalain has been reported as water-soluble, nitrogenous pigments with biological activities. However, their sensitivity to thermal degradation limits their application during food processing. In this report, the interaction of betalain and soy protein isolate fibrils (SPI-F) was investigated through multiple microscopic and spectroscopic techniques and the thermal stability of betalain was assessed after heating treatment. AFM and TEM images showed that the complex of betalain and SPI-F was small, amorphous aggregate. Fluorescence spectroscopy revealed that SPI-F bound with betalain via hydrophobic interactions. Circular dichroism results showed the secondary structures of SPI-F was changed by betalain binding, with a decrease in
-helix (7.5–6.9%), β-turn (13.1–12.9%) and random coil (41.1–40.7%) and an increase in β-Sheet (38.3–39.5%). The addition of SPI-F decreased color loss and increased the thermal retention of betalain from 55.3% to 75.9%. These findings suggest that SPI-F has a protective effect on the thermal stability of betalain and facilitate the widespread application of betalain as natural colorants.
