Phenolic compounds and antioxidant capacities of bayberry juices
Introduction
Bayberry (Myrica rubra Sieb. et Zucc.), belonging to the genus Myrica in the family of Myricaceae, has been cultured in China for more than 2000 years (Chen, Xu, Zhang, & Ferguson, 2004). Due to the exquisite taste, flavour, and attractive red colour, bayberries are popular to local people. Traditionally, bayberry fruits have been used to treat with some gastric intestinal diseases such as diarrhoea and gastroenteritis (Chen, 1996). However, bayberry fruits decay easily, partly because they have no epicarp protection, and ripen in the hot and rainy season of May to July. It was reported that bayberry fruits can only be stored for 3 days at 20–22 °C and 9–12 days at 0–2 °C (Xi & Zheng, 1993). To achieve a longer storage time, bayberry fruits are often processed into juice or juice concentrate.
Phenolic compounds derived from fruits have received more and more attention in recent years because of their bioactive functions (Hollman et al., 1996, Kong et al., 2003, Pellegrina et al., 2005). Berries are one of the most important dietary sources of phenolic compounds, including anthocyanins, phenolic acids, flavonol glycosides and flavan-3-ols (Kähkönen et al., 2001, Määtä-Riihinen et al., 2004). Most bayberries are red or dark red colour, due to the presence of anthocyanins in the fruit. The major anthocyanin in bayberry fruits is cyanidin-3-glucoside which represents more than 95% of the total anthocyanins (Bao et al., 2005, Ye et al., 1994). Flavonol aglycons of myricetin, quercetin and kaempferol (Amakura, Umino, & Tonogai, 2000) and flavonol glycosides (Bao et al., 2005, Fang et al., 2007b) were also detected in bayberry fruits.
Phenolic acids constitute about one-third of the dietary phenols, which may be present in plants in free and bound forms (Robbins, 2003). The distribution and contents of phenolic acids in some berries were investigated by many previous studies (Häkkinen and Törrönen, 2000, Taruscio et al., 2004, Zadernowski et al., 2005), and tens of phenolic acids were identified in berry fruits. However, to our knowledge, only gallic acid and protocatechuic acid were detected in bayberries (Fang et al., 2007b). It seemed that the phenolic acid of bayberries has not been fully identified.
China is the origin of bayberry, and Zhejiang province is the largest province for bayberry production in China (Chen, 1996). Recently, the production and consumption of bayberry juices has increased rapidly, and studies related to bayberry juice processing and stability were also reported (Fang et al., 2007a, Fang et al., 2006). The phenolic compounds (Fang et al., 2007b) and antioxidant capacities of bayberry fruits (Bao et al., 2005) and jam (Amakura et al., 2000) were investigated by some scientists. However, little work has been done on the distribution and contents of phenolic compounds in bayberry juices. The aim of the present study was to analyse the phenolic compounds of bayberry juices from 14 cultivars. Their antioxidant capacities were also evaluated.
Section snippets
Chemicals and reagents
Standards of gallic acid, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid, p-coumaric acid, ferulic acid, quercetin, kaempferol, myricetin, cyanidin-3-O-glucoside, 2,4,6-tris(2-pyridyl)-s-triazine (TPTZ), 6-hydroxyl-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), 2, 2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS+), and Folin-Ciocalteu phenol reagent were purchased from Sigma (St. Louis, MO, USA) and Extrasynthèse (Genay, France). All other chemicals were
Contents of anthocyanin
Anthocyanins possess well-known pharmacological properties and strong biological functions such as anti-inflammatory and antioxidant activities (Kong et al., 2003). In bayberry juices, anthocyanins provide pink, red, and nearly black colours in different cultivars. The HPLC–DAD analysis indicated that only cyanidin-3-glucoside was the detectable anthocyanin in bayberry juices. Similar results were observed in some previous studies (Bao et al., 2005, Fang et al., 2006, Ye et al., 1994). The
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