Alkaline extraction and acid precipitation of phenolic compounds from longan (Dimocarpus longan L.) seeds

The alkaline extraction and acid precipitation of longan seed phenolic compounds were investigated to develop a more practical process than currently exists to isolate these chemicals. By using an alkaline buffer as the extraction solvent, the yield of total phenols reached 46.86±0.43 mg/g after conventional solid-liquid extraction. Because of the benefit achieved from the preconcentration process, an acid precipitation efficiency of 65.29 ± 0.38% was obtained, and the separation yield of phenols reached 22.04 ± 1.95 mg/g. However, the purity of the phenolic extract was influenced by the presence in the precipitate of proteins and carbohydrates, which both moved together in all four precipitation fractions at different pH values. The FRAP assay and the assay of the radical-scavenging activity revealed the strong antioxidant activity possessed by the phenolic compounds in the precipitate extracts. This preparation process for phenolic compounds has obvious advantages, such as easy operation, safe products and low production cost, which indicated its prospective industrial potential.