ABSTRACT

The knowledge of the levels of polyphenols present in green coffee beans from different geographical origins is important to identify beans that can provide better coffee quality. The aim of this study was to determine the concentrations of both soluble and cell wall-bound polyphenols in green coffee beans (Coffea arbica L.) from different cultivation regions of Ethiopia. A total of 100 samples were collected from four geographical regions (East, West, South, Northwest) and comprised eight commercial types of coffee (Harar, Jimma, Kaffa, Wollega, Sidama, Yirgacheffe, Finoteselam and Benishangul). The total concentrations of soluble and cell wall-bound polyphenols and flavonoids in the sample extracts were determined using the Folin-Ciocalteu and aluminum chloride reagent methods, respectively. Qualitative analysis was also performed by using high performance thin layer chromatography (HPTLC). Results revealed that chlorogenic acids as the predominant constituents of the phenolic fraction of the green coffee beans. The total soluble polyphenol, cell wall-bound polyphenol and flavonoid contents of the green coffee beans were in the range of 21.8–43.6 milligrams of gallic acid equivalents per gram (mg GAE g⁻¹), 8.6–15.3 mg GAE g⁻¹ and 3.3–6.2 milligrams of (+)-catechin equivalents per gram (mg CE g⁻¹) of dry mass, respectively. Cell wall-bound polyphenols were found to contribute significantly (21.0–32.5%) to the total polyphenol contents (TPC) of the green coffee beans. The polyphenol contents of green coffee beans have been found to vary with geographical origins. Harar coffee contained significantly (p < 0.05) lower amounts of both total soluble and cell wall-bound polyphenols than the other regional coffee types. Furthermore, the contribution of cell wall-bound phenolic to the TPC should not be overlooked.

摘要

了解来自不同地理来源的生咖啡豆中多酚含量的知识对于确定可以提供更好咖啡品质的咖啡豆很重要。这项研究的目的是确定绿色咖啡豆（咖啡树）中可溶性和细胞壁结合多酚的浓度L.）来自埃塞俄比亚的不同种植地区。总共从四个地理区域（东，西，南，西北）收集了100个样品，其中包括八种商业类型的咖啡（哈勒尔，吉马，卡法，沃勒加，西达玛，伊尔加切夫，菲诺瑟兰和贝尼桑古尔）。样品提取物中可溶性和细胞壁结合的多酚和类黄酮的总浓度分别使用Folin-Ciocalteu法和氯化铝试剂法测定。还通过使用高效薄层色谱（HPTLC）进行了定性分析。结果表明，绿原酸是生咖啡豆酚类成分的主要成分。生咖啡豆的总可溶性多酚，与细胞壁结合的多酚和类黄酮含量在21.8–43范围内。^-1），每克干物质（mg CE g ^-1）分别有8.6-15.3 mg GAE g ^-1和3.3-6.2毫克（+）-儿茶素当量。发现与细胞壁结合的多酚对生咖啡豆的总多酚含量（TPC）有显着贡献（21.0–32.5％）。发现生咖啡豆的多酚含量随地理来源而变化。哈拉尔咖啡所含的总可溶物和与细胞壁结合的多酚含量均显着低于其他区域性咖啡类型（p <0.05）。此外，细胞壁结合酚对TPC的贡献也不容忽视。