Flavonoid process

Chebil L, Humean C, Falcimaigne A, Engasser JM, Ghoul M. 2006. Enzymatic acylation of flavonoids. Process Biochem 41 2237-2251. 

Some of the potential uses of the fats and oils found in plants have been reviewed and some uses of carbohydrate-based polymers briefly discussed. Plants contain a whole variety of other chemicals including amino acids, terpenes, flavonoids, alkaloids, etc. When the potential for these naturally occurring materials are combined with the secondary products that can be obtained by fermentation or other microbial processes or by traditional chemical transformations, the array of chemicals that can readily be created from renewable resources is huge. In this section a few of the more interesting examples are considered. 

Evaporation is the oldest process for the concentration of liquid foods. Temperatures are higher compared to those of the more modern membrane filtration or freeze concentration processes. Tocopherols, carotenes, ascorbic acid, flavonoids and other phenolic antioxidants are partially destroyed by heating. Therefore, it is necessary to minimise the time needed for evaporation, and heating to the evaporation temperature should be carried out very rapidly. The temperature may be decreased if the pressure is reduced. The process is then more expensive, but losses of antioxidants become substantially lower. 

EWALD C, FJELKNER MODIG S, JOHANSSON K, SJOHOLM I and AKESSON B (1999) Effect of processing on major flavonoids in processed onions, green beans, and peas . Food Chem, 64 (2) 231-5. 

There has been some evidence of a higher antioxidant effect when both flavonoids and a-tocopherol are present in systems like LDL, low-density lipoproteins (Jia et al., 1998 Zhu et al, 1999). LDL will incorporate a-tocopherol, while flavonoids will be present on the outside in the aqueous surroundings. A similar distribution is to be expected for oil-in-water emulsion type foods. In the aqueous environment, the rate of the inhibition reaction for the flavonoid is low due to hydrogen bonding and the flavonoid will not behave as a chain-breaking antioxidant. Likewise, in beer, none of the polyphenols present in barley showed any protective effect on radical processes involved in beer staling, which is an oxidative process (Andersen et al, 2000). The polyphenols have, however, been found to act synergistically... 

The shikimate pathway is the major route in the biosynthesis of ubiquinone, menaquinone, phyloquinone, plastoquinone, and various colored naphthoquinones. The early steps of this process are common with the steps involved in the biosynthesis of phenols, flavonoids, and aromatic amino acids. Shikimic acid is formed in several steps from precursors of carbohydrate metabolism. The key intermediate in quinone biosynthesis via the shikimate pathway is the chorismate. In the case of ubiquinones, the chorismate is converted to para-hydoxybenzoate and then, depending on the organism, the process continues with prenylation, decarboxylation, three hydroxy-lations, and three methylation steps. - ... 

Flavonoids may be extracted from fresh or frozen plant tissues or from herbarium material, although freeze-dried material may also be utilized [34]. It is very important to ensure that the matoial to be extracted is finely divided, whether by cutting or emshing, to ensure proper extraction. Extraction can be carried out successively with methanol containing some 10% of wate and thm with a 1 1 mixture of methanol and water. Each extraction should be carried out for a period of about 2 h, shaking or stirring to facilitate the process. The extracts are then combined for chromatographic separation. 

Ring B and the central three-carbon bridge forming the C ring (see Fig. 5.1) originate from the amino acid phenylalanine, itself a product of the shikimate pathway, a plastid-based process which generates aromatic amino acids from simple carbohydrate building blocks. Phenylalanine, and to a lesser extent tyrosine, are then fed into flavonoid biosynthesis via phenylpropanoid (C6-C3) metabolism (see Fig. 5.1). 

Gil MI, Ferreres F and Tomas-Barberan FA. 1998. Effect of modified atmosphere packaging on die flavonoids and vitamin C content of minimally processed Swiss chard (Beta vulgaris subsp. cycla). J Agric Food Chem 46 2007-2012. 

Lee SU, Lee JH, Choi SH, Lee JS, Ohnisi-Kameyama M, Kozukue N, Levin CE and Friedman M. 2008. Flavonoid content in fresh, home-processed, and light-exposed onions and in dehydrated commercial onion products. J Agric Food Chem 56(18) 8541—8548. 

There are several mechanisms involved in the vasodilator effect of flavonoids. The main mechanism seems to be related to the inhibition of protein kinase C or some of the processes activated by this protein. The inhibition of other protein kinases and cyclic nucleotide phosphodiesterase activity and blockage of calcium entry can also contribute to this effect to a greater or lesser extent (Alvarez Castro and Orallo, 2003 Herrera and others 1996). Certain flavonoids, like the flavonol myricetin, have a two-phase action on blood vessels vasoconstrictor in lowest active concentrations and vasodilator in higher concentrations (Alvarez Castro and Orallo, 2003). 

---