Changes of phenolic acids and antioxidant activities during potherb mustard (Brassica juncea, Coss.) pickling
Introduction
Potherb mustard (Brassica juncea, Coss.), belonging to the family of Cruciferae, is a leafy vegetable cultivated in China (Liu, 1994). A single plant of potherb mustard may have as many as 150–200 leaves clustered together in a compact bunch of 20–30 cm diameter. Potherb mustard is consumed not only in cooked and raw fresh vegetables, but also in salt-preserved or pickled forms. Pickled potherb mustard is a traditional fermented vegetable product and is widely consumed by all social groups in China (Li, 1988). The quality characteristics of potherb mustard pickles are due to its typical flavour and taste, and the major flavour components are mainly derived from glucosinolate hydrolysis. The predominant glucosinolates in potherb mustard are sinigrin, gluconapin, glucocochlearin and gluconasturtin (Zhao, Tang, & Ding, 2007). During pickling, these glucosinolates can be hydrolysed to the products of isothiocyanates or indole-3-carbinol (Kameoka and Hashimoto, 1980, Masuda et al., 1996), resulting in alleviation of the pungent flavour and endowing the pickled vegetable with a special savoury flavour. Interestingly, the glucosinolate hydrolysis products such as isothiocyanates and indole-3-carbinol are capable of modulating enzyme activity and preventing certain cancers (Fahey et al., 1997, Greenwald, 2004).
Phenolic compounds in vegetables are also beneficial to the health of human beings (Tomás-Barberán and Robins, 1997, Verhoeven et al., 1996). Their high antioxidant capacities are thought to have links with the inhibition of oxidative damage diseases, such as coronary heart disease, stroke, and cancers (Block et al., 1992, Huang and Ferraro, 1992, Powles and Ness, 1996). The main flavonols in potherb mustard are quercetin and kaempferol, and flavonol contents range from 6.51 to 14.9 mg/g dry weight, which are positively correlated with antioxidant activities. The contents of antioxidant compounds and antioxidant activities are lower in pickled leaf mustard compared with fresh samples (Wang & Zhu, 2006a). Antioxidant activities in pickled products are also significantly correlated with their contents of total phenolics (Wang & Zhu, 2006b).
As a high dietary intake of cruciferous vegetables is thought to be desirable for preventing certain cancers (Suzuki, Ohnishi-Kameyama, Sasaki, Murata, & Yoshida, 2006), development of methods for retaining these functional compounds is expected to aid in the production of cruciferous vegetable products with greater health benefits.
Potherb mustard is one of the most popular and important cruciferous vegetables in China. However, information on the chemical components, especially the phenolic acids, of fresh and pickled potherb mustard is limited. In this study, we analysed the phenolic acids in the potherb mustard, and their changes during the pickling processes were monitored. The antioxidant activities of these foods evaluated with different methods were also investigated.
Section snippets
Chemicals and reagents
Standards of gallic acid, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid, p-coumaric acid, ferulic acid, sinapic acid, 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). All other chemicals used were of analytical grade.
Materials
Fresh potherb mustard was harvested from a farm field in the
Phenolic acids and total phenolics contents in potherb mustard
Efficient separations of potherb mustard phenolic acids were achieved; Fig. 1 shows the HPLC chromatogram of the free phenolic acids. By comparison with standards, gallic acid, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid, p-coumaric acid, ferulic acid, and sinapic acid were identified in the fresh potherb mustard. Although chlorogenic acid is the main phenolic acid in many other foods (Mattila & Kumpulainen, 2002), it was not detected in potherb mustard. Flavonols of
Conclusion
Phenolic acids have received considerable attention as potentially protective factors against cancer and heart diseases, in part because of their potent antioxidative properties and their ubiquity in a wide range of commonly consumed foods of plant origin (Breinholt, 1999, Shahidi and Naczk, 1995). The results of the present study showed that pickling processes were relatively good methods for the preservation of phenolic acids in potherb mustard, and most of the antioxidant capacities remained
Acknowledgements
This work was partially supported by a program of “Significance of N, S and Se supply for the quality of Chinese Brassica-type vegetables with special reference to glucosinolates and selenium” (No. GZ051-10(154)), founded by the Sino-German Center for Research Promotion, and National Natural Science Foundation of China.
References (31)
- et al.
The ferric reducing ability of plasma (FRAP) as a measure of “antioxidant power”: The FRAP assay
Analytical Biochemistry
(1996) - et al.
Controlling cabbage fermentations with nisin and nisin resistant Leuconostoc mesenteroides
Food Microbiology
(1995) Clinical trials in cancer prevention: Current results and perspectives for the future
Journal of Nutrition
(2004)- et al.
Antioxidant activity applying an improved ABTS radical cation decolorization assay
Free Radical Biology & Medicine
(1999) - et al.
Effect of blanching on phenolics and radical scavenging activity of highbush blueberry juice
Food Research International
(2003) - et al.
Dietary intake and bioavailability of polyphenols
Journal of Nutrition
(2000) - et al.
Analysis of volatile components during potherb mustard (Brassica juncea, Coss.) pickle fermentation using SPME–GC–MS
LWT – Food Science and Technology
(2007) - et al.
Influence of jam processing on the radical scavenging activity and phenolic content in berries
Journal of Agricultural and Food Chemistry
(2000) - et al.
Fruit, vegetables, and cancer prevention: A review of the epidemiological evidence
Nutrition and Cancer
(1992) Desirable versus harmful levels of intake of flavonoids and phenolic acids