Flavonoid compounds in foods

Knowledge of the identity of phenolic compounds in food facilitates the analysis and discussion of potential antioxidant effects. Thus studies of phenolic compounds as antioxidants in food should usually by accompanied by the identification and quantification of the phenols. Reversed-phase HPLC combined with UV-VIS or electrochemical detection is the most common method for quantification of individual flavonoids and phenolic acids in foods (Merken and Beecher, 2000 Mattila and Kumpulainen, 2002), whereas HPLC combined with mass spectrometry has been used for identification of phenolic compounds (Justesen et al, 1998). Normal-phase HPLC combined with mass spectrometry has been used to identify monomeric and dimeric proanthocyanidins (Lazarus et al, 1999). Flavonoids are usually quantified as aglycones by HPLC, and samples containing flavonoid glycosides are therefore hydrolysed before analysis (Nuutila et al, 2002). 

Miyake, Y. et al., Isolation of C-glucosylflavone from lemon peel and antioxidative activity of flavonoid compounds in lemon fruit, J. Agric. Food Ghem., 45, 4619, 1997. 

Bramati, L. et al.. Quantitative characterization of flavonoid compounds in Rooibos tea (Aspa-lathus linearis) by LC-UV/DAD, J. Agric. Food Chem., 50, 5513, 2002. 

Rhodes, M.J.C. and Price, K.R., Analytical problems in the study of flavonoid compounds in onions. Food Chem., 57, 113, 1996. 

Owen RW, Haubner R, Mier W, Giacosa A, Hull WE, Spiegelhalder B, Bartsch H. 2003. Isolation, structure elucidation and antioxidant potential of the major phenolic and flavonoid compounds in brined olive drupes. Food Chem Toxicol 41 703-717. 

Cortell, J., Kennedy, J. A. (2006). Effect of shading on accumulation of flavonoid compounds in (Vitis vinifera L.) Pinot Noir fruit and extraction in a model system. J. Agric. Food Chem., 54, 8510-8520. 

Different spectrophotometric methods for the quantification of phenolic compounds in foods have been developed. Spectrophotometric methods are based on the formation of a compound or colored complex that is measured at a certain wavelength. To avoid interference, an effective extraction of flavonoids is necessary before spectrophotometric measurement. 

This chapter will focus on developments in rice bran oil and sesame seed oil, both of which have exceptional oxidative stability and diverse biological activity. In addition, rosemary antioxidants will be described, with an account of methods for extracting bioactive compounds and a discussion of the stability of these compounds in food systems. Recent literature on the stability and health benefits of flavonoids will complete the chapter. 

Although not all-inclusive, these studies demonstrate that the structure of a flavonoid has a significant role in dictating its biological activity. A growing body of evidence supports the claimed health benefits of flavonoids. The development of functional foods using flavonoids will depend on the stability of these compounds in food systems. 

Despite many advantages, MS/MS detection is not sufficient to determine the molecular formula of an unknown. Mass spectrometers with ion trap are able to identify new, unknown polyphenolic compounds in food samples, which are characterized by their ability to detect MS experiments. They can generate fragmentation of ions in n generations, which is particularly crucial in the analysis of isomer glycoside flavonoids. The resolution of the masses, achieved by the ion trap mass spectrometer, is comparable to that of the quadrupole mass spectrometers. 

There are numerous synthetic and natural compounds called antioxidants which regulate or block oxidative reactions by quenching free radicals or by preventing free-radical formation. Vitamins A, C, and E and the mineral selenium are common antioxidants occurring naturally in foods (104,105). A broad range of flavonoid or phenoHc compounds have been found to be functional antioxidants in numerous test systems (106—108). The antioxidant properties of tea flavonoids have been characterized using models of chemical and biological oxidation reactions. 

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