高氧胁迫促进发芽薏米富集多酚类物质的机理研究

Adlay (Coix lachryma-jobi L.) has long been used as a food source as well as an herbal medicine due to its high nutritional and medicinal values. Although China is a major adlay cultivation and consumption country, the processing of adlay in China is still on the initial stage. Polyphenols are important secondary metabolites of adlay and exhibit a wide range of physiological and pharmacological activities relevant to human health. Therefore, exploring an efficient method for enriching adlay polyphenols can help improve its economic and social benefits. In previous studies, we found that hyperoxia stress can induce accumulation of phenolics in germinated adlay. However, the mechanism for the hyperoxia-induced accumulation of phenolics in germinated cereal remains unknown. The present project intends to investigate the changes of physiological and biochemical properties and the activities and gene expression of key enzymes relevant to polyphenol synthesis in germinated adlay under different conditions of hyperoxia stress so as to uncover the relationships between primary metabolites, key enzymes, gene expression and the accumulation of secondary metabolites under hyperoxia stress. Further, the induction of polyphenol accumulation by NO and H2O2 under hyperoxia stress was further studied, and the signal transduction mechanism was clarified. These studies will provide the theoretical basis for the mechanism of the synthesis of secondary metabolites in germinated adlay under hyperoxia stress, and also provide technical parameters for the further use of hyperoxia stress to better regulate the production of secondary metabolites.

薏米是一种广泛应用的药食两用资源，中国是薏米种植和消费大国，然而当前我国的薏米加工尚停留在初级阶段。多酚类物质是薏米中的一类重要的次生代谢产物，对人体具有广泛的生理和药理活性，因此探索高效的薏米多酚富集方法有助于提高其经济和社会效益。本项目申请人在前期的研究中发现，高氧胁迫处理能显著提高发芽薏米的多酚类物质含量。然而，国内外关于高氧胁迫影响谷物发芽过程中多酚富集的机理尚无明确阐述。本项目拟对不同高氧胁迫条件下发芽薏米的生理生化和多酚合成关键酶酶活、基因表达的变化规律进行研究，揭示高氧胁迫下初级代谢产物、多酚合成关键酶以及基因表达与次级代谢产物积累的关系，在此基础上进一步研究高氧胁迫下NO和H2O2对多酚积累的诱导作用，明确高氧胁迫下多酚合成的信号转导机制。通过本项目的实施，以期为高氧胁迫下薏米次生代谢物合成机制提供理论基础，进而为以后利用高氧胁迫更好地调控次生代谢物的产量提供技术参数。

目前发芽已被证实是一种廉价但有效的谷物加工方法，发芽处理可以进一步提高谷物的营养价值和生物活性。然而，目前国内外关于高氧胁迫对谷物发芽影响的报道很少，对于此问题的探究可促进谷物多酚富集方法、富集机制的发展。首先，我们阐明了高氧胁迫下发芽薏米中多酚含量富集与薏米籽粒生理生化特性、多酚合成关键酶酶活及其基因表达变化的内在关联。然后，我们探寻了高氧胁迫下NO对薏米萌发过程中多酚类物质富集的诱导作用，揭示高氧胁迫富集多酚的信号转导机制。此外，我们还研究了不同发芽时间的薏米在发酵后蛋白质、多肽、氨基酸、总酚、抗氧化活性、黄嘌呤氧化酶和酪氨酸酶抑制活性的变化，可为基于薏米的健康功能食品、化妆品的研发提供技术支撑。研究发现高氧胁迫通过提高酚类物质合成关键酶PAL、C4H、4CL活力，增加发芽薏米总酚含量。高氧胁迫处理激活NOS和NR活力，诱导发芽薏米中NO合成，NO进一步参与发芽薏米酚类物质合成。干酪乳杆菌发酵可进一步改善发芽薏米的营养组成，提高其生物活性。随着发酵时间的延长，发芽薏米蛋白质发生显著降解，低分子量多肽比例和面积显著提高，游离氨基酸含量显著增加。发芽薏米在发酵后，水提取液总酚含量显著提高，铁离子还原能力（FRAP）及清除ABTS·+能力显著增强。此外，发芽薏米水提取液的黄嘌呤氧化酶和酪氨酸酶抑制活性在发酵后显著提高。