Isolation and characterization of melanin from palm fiber

ABSTRACT

Melanin pigments derived from palm fiber were isolated via acid/ethanol extraction, acid hydrolysis, organic solvent (e.g., ethanol, ethyl acetate, and acetone) treatment, and repeated precipitation. Ultraviolet-visible and infrared spectra analyses showed that the melanin pigments derived from palm fiber were similar to typical melanin. The stability of palm fiber pigments in oxidants, reducing agents, metal ions, temperature, and light was investigated. Results revealed that the stability of palm fiber pigments was good in the oxidant, hydrogen peroxide, but relatively poor in the reducing agent, sodium sulfite. The derived melanin pigments were significantly affected by Fe³⁺, Al³⁺, Cu²⁺, and Zn²⁺, but only slightly affected by Na⁺, Mg²⁺, and Ca²⁺. In addition, palm fiber pigments exhibited poor thermal endurance at high temperatures and under room lighting. A study on antioxidant activity showed that palm fiber pigments exhibited strong scavenging capability against free radicals. Moreover, its removal capability was enhanced by increasing pigments concentration. Its scavenging capability was arranged from weak to strong as follows: 1,1-diphenyl-2-picrylhydrazyl• < ${{\mathrm{O}}_2}^{-}$• < •OH.

摘要

用酸/乙醇萃取、酸水解、有机溶剂（如乙醇、乙酸乙酯和丙酮）处理，并反复沉淀分离得到棕色素。紫外可见光谱和红外光谱分析表明，棕榈纤维中的黑色素与典型的黑色素相似。研究了棕榈纤维颜料在氧化剂、还原剂、金属离子、温度、光照等方面的稳定性。结果表明，棕榈纤维色素在氧化剂、过氧化氢中的稳定性较好，还原剂亚硫酸钠的稳定性较差。导出的黑色素是由Fe3+、Fe³⁺, Al³⁺, Cu²⁺, 和Zn²⁺,的显著影响，但影响不大，Na⁺, Mg²⁺, 和Ca²⁺。此外，棕榈纤维颜料在高温下和室内照明下表现出较差的耐热性。抗氧化活性的研究表明，棕榈纤维色素对自由基具有较强的清除能力。提高颜料浓度可提高其去除能力。其清除能力呈由弱到强如下：1,1-diphenyl-2-picrylhydrazyl • <O₂^–• < •OH。

KEYWORDS:

• Melanin pigment
• palm fiber
• physical and chemical properties
• inoxidizability

关键词:

• 黑色素；棕榈纤维；理化性质；耐腐蚀性

Additional information

Funding

This work was supported by the Fundamental Research Funds for the Central Universities [XDJK2017D045].