Phenolic compounds participating in mulberry juice sediment formation during storage

Abstract

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.

摘要

目 的

探讨澄清型桑果汁贮藏期间酚类物质的变化规律, 明确沉淀形成的主要物质基础。

创新点

首次研究了桑果汁贮藏期间上清和沉淀中酚类物质的变化规律, 阐明了酚类物质参与桑果汁沉淀形成的机制, 明确了花色苷是沉淀形成的主要物质基础。

方 法

对贮藏期间桑果汁的上清和沉淀进行了分离, 提取了游离态和结合态多酚, 对总酚含量的变化进行了研究, 并采用高效液相色谱法和高效液相色谱质谱联用法对酚类化合物的组成进行了定性和定量分析。

结 论

随着贮藏时间的延长, 桑果汁的沉淀量逐渐增加 (图1), 果汁上清液和沉淀游离酚的总酚含量逐渐下降, 而沉淀结合酚则呈现上升趋势 (图2) 。上清液和沉淀中游离态花色苷分别从 938.60 和235.60 mg/L 下降到 2.30 和 1.74 mg/L (表2), 上清中黄酮类物质也有所下降, 而沉淀中结合态的没食子酸、原儿茶酸、咖啡酸和芦丁的含量则呈上升趋势 (表2) 。桑果汁贮藏8 周后, 沉淀中的花色苷占酚类物质总量的67.2% (表2) 。综上所述, 酚类物质参与了桑果汁沉淀的形成, 其中花色苷起主要作用。