Abstract：
Lotus rhizome is an important aquatic vegetable, but the blackening of lotus rhizome epidermis (LRE) seriously affects its appearance and quality, which makes lotus rhizome products unmarketable. In this study, the effects of polyphenols and iron on the LRE color were studied to explore the possible mechanism of LRE blackening. Results indicated that the measurable total phenols contents in the mud treatment (MT) group were significantly reduced, and the total iron contents were significantly increased compared with the bruised treatment group (p < 0.05). The high-performance liquid chromatography results showed that the main polyphenols in LRE were dopa, gallocatechin, and catechin, as well as a small amount of catechol, epicatechin, proanthocyanidin B2, and proanthocyanidin C1. Moreover, the results of color difference and ultraviolet adsorption spectroscopy showed that there were obviously black or brown-gray of dopa (525 nm), gallocatechin (504.5 nm), and catechin (550 and 504.5 nm) with FeCl2. The simulated system treatment of LRE further confirmed that the chromaticity effect of dopa and iron in bruised LRE was similar to that of the MT group, whereas 1% (w/w) ascorbic acid, 2% (w/w) EDTA-2Na, or 3% (w/w) citric acid could solely prohibit the blackening. This suggested that the dopa in LRE and FeCl2 in mud may mainly combine into [2(DOPA-2H+)+Fe3+]- through non-covalent interaction, which leads to the blackening of bruised LRE under neutral conditions. These results can guide the storage of lotus rhizomes and improve the development of the lotus rhizome industry.
摘要：
莲花根茎是一种重要的水生蔬菜,但莲花表皮变黑严重影响其外观和品质,这使得莲子产品无法销售。在这项研究中,研究了多酚和铁对LRE颜色的影响，探讨了LRE发黑的可能机理。结果表明，泥浆处理（MT）组中可测量的总酚含量显着降低，与瘀伤治疗组相比，总铁含量显着增加（p<0.05）。高效液相色谱结果表明,LRE中主要的多酚为多巴,gallocatechin,和儿茶素,以及少量的儿茶酚，表儿茶素,原花青素B2和原花青素C1。此外，色差和紫外吸收光谱结果表明，多巴呈明显的黑色或棕灰色(525nm)，gallocatechin(504.5nm),和儿茶素(550和504.5nm)与FeCl2。LRE的模拟系统处理进一步证实，多巴和铁在挫伤LRE中的色度效应与MT组相似，而1%(w/w)抗坏血酸，2%(w/w)EDTA-2Na,或3％（w/w）柠檬酸可以单独阻止变黑。这表明LRE中的多巴和泥浆中的FeCl2可能主要通过非共价相互作用结合成[2(DOPA-2H+)+Fe3+]。这导致在中性条件下擦伤的LRE变黑。这些结果可以指导莲子的贮藏，促进莲子产业的发展。
