传统乌米饭加工食用过程中色素着色及稳定调控机制研究

WuMiFan is a traditional healthy rice food, which had been consumed for centuries in parts of eastern coastal region of China. Vaccinium Bracteatum Thunb., the mainly ingredient for preparing WuMiFan, is a resource of traditional Chinese herbal medicine, which belongs to the genus Rhododendron. Some physiological functions of Vaccinium Bracteatum Thunb. leaf (VBTL) had been recorded in compendium of materia medica, such as anti-fatigue, digestion resistibility and antioxidant activity. Some properties and functions of the black pigment extracted from VBTL including UV absorption, stability, and dyeing ability were determined. Recently, many healthy functions of VBTL had been reported, including antioxidant activity, protective effect against light injury of retina, and anti-diabetic activity. However, WuMiFan had not been industrial produced for its special preparing process, seasonal restriction of VBTL, and unclear underlying dyeing mechanism. .In this research, we aimed to investigate the interaction between VBTL pigment and rice components by using a combination of proteomic and biochemical strategies in light of the absence of relevant studies. We developed a simplified model system in which pigment was incubated with isolated classified rice protein and starch. We measured changes in VBTL pigment polyphenol content and antioxidant activity during the interaction and applied proteomic strategies, such as surface hydrophobicity and Fourier-transform infrared spectroscopy (FT-IR), to monitor various aspects of the rice protein and starch. The data acquired in this manner allowed us to characterize interaction patterns between VBTL pigment and rice protein/starch in detail, which was helpful to establish the regulation method for industrial producing WuMiFan.

乌米饭是一种在江、浙、闽等沿海省份有悠久食用习俗的传统健康谷物食物，其主要原料——乌饭树树叶具有抗氧化、预防视网膜光损伤、调节血糖血脂等多种生理功能。受季节性强和特殊制作工艺的限制，乌米饭尚未实现产业化，主要原因在于色素着色机理及其调控机理不清晰。本项目以乌饭树树叶和不同类型的大米为原料，制备乌米饭，对色素的染色过程、乌米饭的制备过程进行深入研究。在分析色素和大米主要组分物理化学特性的基础上，深入研究染色过程中色素和大米不同组分之间的结合方式，揭示色素与大米组分在染色过程中的变化规律；以不同的蒸煮条件为手段，研究色素-蛋白质、色素-淀粉结合物的热稳定性；从色素和大米组分的自身变化、结合方式对染色效果影响、对结合物热稳定性影响等多个层次的分析，从定性/定量、宏观/微观、动态/静态等方面，研究黑色素以及大米中不同组分在染米过程中发生的变化，揭示乌饭树黑色素染色机理，并进而探讨其调控机制。

本项目主要围绕传统乌米饭加工食用过程中色素着色及稳定调控机制展开研究，从乌饭树树叶色素呈色机理入手，首次在乌饭树树叶次级代谢物中筛选出色素前体物质，阐释了基于色素前体物质变化导致的色素季节性差异，深入分析了色素的呈色反应动力学、加工稳定性及其与食品组分的相互作用，并探讨了色素对α-淀粉酶的抑制活性。结果发现乌饭树树叶色素前体物质主要为环烯醚萜苷类物质，含氨基化合物是色素形成的另一重要底物；通过进一步分析乌饭树树叶中色素辅助因素分析和反应过程中间产物检测，发现酸性条件和β-葡萄糖苷酶是色素形成的辅助因素；不同季节树叶中环烯醚萜苷和氨基酸含量、种类的差异是造成蓝黑色素季节性差异的主要原因，并利用色素反应底物探究了呈色反应动力学变化规律，得到色素反应的优化参数：反应温度70℃，反应时间3h，反应体系pH4.0；色素产物中增加了C-N键官能团，其耐酸性、耐热性、耐盐性较好，而耐氧化性和耐还原性较弱，色素可以显著影响大米淀粉的热力学特性、糊化特性等理化性质；此外，色素在模拟胃肠消化过程中色素保留率可超过65%，色素对猪胰α-淀粉酶具有较好的抑制作用，IC50值为3.692mg/mL；通过抑制动力学分析可知色素是一种非竞争性的抑制剂，通过荧光发射光谱和圆二色谱分析发现，色素改变了α-淀粉酶的二级结构和活性位点构象，以起到对α-淀粉酶的抑制作用。本项目为乌米饭加工食用过程中的色素调控提供了科学依据，也为新型乌饭树树叶色素的开发奠定了理论基础。