Food Biochemistry and Food Processing (2 edition)

BLBS102-c28 BLBS102-Simpson March 21, 2012 13:54 Trim: 276mm X 219mm Printer Name: Yet to Come

28 Biochemistry of Fruit Processing 567

O

OH

OH

A C

B

O

OH

OH

OH

OH

+

OH

OH

O

OH

OH

OH

O

OH

O

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH O

Biflavan

Flavans

Flavonone

Blueberries

Cherries

Wine

Anthocyanin

Catechin

Apples

Peaches

Te a

Citrus

Figure 28.7.Chemical structures of fruit flavonoids. The propanoid structure consists of two fused rings. “A” is aromatic ring and “C” is a

heterocyclic ring attached by carbon–carbon bond to “B” ring. The flavonoids differ in their structure at the “B” and “C” rings.

legumes. Structurally, flavonoids are characterized by a C 6 -C 3 -

C 6 carbon skeleton (Fig. 28.7). They occur as aglycones (without

sugar moieties) and as glycosides (with sugar moieties). Process-

ing may decrease the content of flavonoids by up to 50%, due to

leaching into water or removal of portions of the fruit such as the

skin, that are rich in flavonoids and anthocyanins. It is estimated

that the dietary intake of flavonoids may vary from 23 mg/d to

1000 mg/d in various populations (Peterson and Dwyer 1998).

Flavonoids are increasingly recognized as playing potentially

important roles in health including but not limited to their roles

as antioxidants. Epidemiological studies suggest that flavonoids

may reduce the risk of developing cardiovascular diseases

and stroke.

Flavanones

The major source of flavanones is citrus fruits and juices.

Flavanones contribute to the flavor of citrus, for example,

naringin found in grapefruit provides the bitter taste, whereas

hesperidin, found in oranges is tasteless.

Flavonols

The best-known flavonols are quercetin and kaempferol.

Quercetin is ubiquitous in fruits and vegetables. Kaempferol

is most common among fruits and leafy vegetables. In fruits,

flavonols and their glycosides are found predominantly in the

skin. Myricetin is found most often in berries.