Sericultural & Agri-Food Research Institute, Guangdong Academy of Agricultural Sciences / Key Laboratory of Functional Foods, Ministry of Agriculture / Guangdong Key Laboratory of Agricultural Products Processing, Guangzhou 510610, China.
J Zhejiang Univ Sci B. 2017;18(10):854-866. doi: 10.1631/jzus.B1600461.
The stability of clarified juice is of great importance in the beverage industry and to consumers. Phenolic compounds are considered to be one of the main factors responsible for sediment formation. The aim of this study is to investigate the changes in the phenolic content in clarified mulberry juice during storage. Hence, separation, identification, quantification, and analysis of the changes in the contents of phenolic compounds, both free and bound forms, in the supernatant and sediments of mulberry juice, were carried out using high performance liquid chromatographic system, equipped with a photo-diode array detector (HPLC-PDA) and HPLC coupled with quadrupole-time of flight mass spectrometric (HPLC-QTOF-MS/MS) techniques. There was an increase in the amount of sediment formed over the period of study. Total phenolic content of supernatant, as well as free phenolic content in the extracts of the precipitate decreased, whereas the bound phenolic content in the sediment increased. Quantitative estimation of individual phenolic compounds indicated high degradation of free anthocyanins in the supernatant and sediment from 938.60 to 2.30 mg/L and 235.60 to 1.74 mg/g, respectively. A decrease in flavonoids in the supernatant was also observed, whereas the contents of bound forms of gallic acid, protocatechuic acid, caffeic acid, and rutin in the sediment increased. Anthocyanins were the most abundant form of phenolics in the sediment, and accounted for 67.2% of total phenolics after 8 weeks of storage. These results revealed that phenolic compounds, particularly anthocyanins, were involved in the formation of sediments in mulberry juice during storage.
澄清果汁的稳定性在饮料行业和消费者中都非常重要。酚类化合物被认为是导致沉淀形成的主要因素之一。本研究旨在研究澄清桑果汁在储存过程中酚类物质含量的变化。因此，使用配备有光电二极管阵列检测器（HPLC-PDA）和高效液相色谱-四极杆飞行时间质谱联用（HPLC-QTOF-MS/MS）技术的高效液相色谱系统，对上清液和沉淀物中游离和结合形式的酚类化合物的含量进行分离、鉴定、定量和分析。在研究期间，形成的沉淀物数量增加。上清液中总酚含量以及沉淀提取物中的游离酚含量降低，而沉淀物中结合酚含量增加。对个别酚类化合物的定量估计表明，上清液和沉淀物中的游离花青素分别从 938.60 至 2.30mg/L 和 235.60 至 1.74mg/g 高度降解。上清液中类黄酮含量也有所下降，而沉淀物中结合形式的没食子酸、原儿茶酸、咖啡酸和芦丁含量增加。花青素是沉淀物中酚类物质的主要形式，在储存 8 周后，占总酚类物质的 67.2%。这些结果表明，酚类化合物，特别是花青素，在桑果汁储存过程中参与了沉淀物的形成。
