The Role of Polyphenols in Quality, Postharvest Handling, and Processing of Fruits - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 263

Table 12.2 Concentrations (mg/100 g fresh weight) of phenolics of selected fruit crops

Total Hydroxycinnamic Flavan-

Fruit phenols acid derivatives Anthocyanins Flavonols 3-ols Tannins

10-2,160 (P a ) Apples 50-1,100 6-134 18-41 (P) 0.2-16 400-3,500

Blueberry 381-4,651 188-211 160-503 2.4-2.9 5-20

Cranberry 46-172 14-33 6-20 100

Grape (white) 350 (P) 1.3-87 (P) 0 8.1-8.2 1.4-53 (P) 17 (P)

Grape (red) 900-950 10-109 (P) 8.388 1.9-10 220-370 32-78 (P)

Orange 831 14-16 050-100

Peach 28-180 8-75 0 0.4-1 5.3-14 90-120

Pear 123-400 170 5-10 (P) 4-160 (P) 0.1-6.2 53

Plum 167-200 12-94 2-5.3 2-5.2 1.8-6.1 76-150

Strawberry 85 1.4-3.1 28-70 2.1-17 2.4-9.6 110-150

Adapted from Kalt (2001).
a “P” indicates the peel tissue.

and other hydroxycinnamates in fruits and fruit products especially wine and cider are
primarily responsible for bitterness and astringency (Marvin and Nagel, 1982).
Chlorogenic acids possess various antioxidant properties. In an in vitro study by Meyer
et al. (1998), chlorogenic has been shown to inhibit the oxidation of low-density lipoprotein
(LDL) by 86-91% at a concentration of 5 M. The prevention of LDL oxidation has been

associated with decreased incidence of atherogenesis and coronary heart disease. Chloro-
genic acid has also been attributed to having inhibitory effects on glucose-6-phosphate
translocase (Gl-6-P translocase). This in turn can reduce the hepatic glucose production
and the severity of non-insulin-dependent diabetes mellitus (Hemmerle et al., 1997). Anti-
carcinogenic activity has also been shown to exist in chlorogenic acid. Chan et al. (1986)
have demonstrated that chlorogenic acid has the ability to suppress the mutagenic proper-
ties of N -methyl- N -nitro- N -nitrosoguanidine (MNNG) in Salmonella typhimurium strain
TA1535. By feeding hamsters a diet composed of 0.025% chlorogenic acid for 24 weeks,
the incidence of methylazoxymethanol acetate-induced liver and bowel cancer was reduced
(Mori et al., 1986).

μ

12.4 Distribution of flavonoids in fruits

Flavonoids represent the most common and widely distributed group of phenolics in fruits.
More than 6,000 different flavonoids have been characterized from higher plants. Their
common structure is C 6 C 3 C 6 and consists of two aromatic rings linked through three
carbons that usually form an oxygenated heterocycle (Harborne, 1980). Figure 12.1 shows
the basic structure and the system used for the carbon numbering of the flavonoid nucleus.
Structural variations within the rings subdivide the flavonoids into several families: fla-
vanone, flavonols, flavones, flavanols, anthocyanidins, dihydrochalcones, and others. These
flavonoids often occur as glycosides, glycosylation rendering the molecule more water sol-
uble and less reactive toward free radicals. Further modification occurs at various stages,
resulting in an alteration in the extent of hydroxylation, methylation, isoprenylation, dimer-
ization, and glycosylation (producing O- or C-glycosides). The sugar most commonly
involved in glycoside formation is glucose, although galactose, rhamnose, xylose, and
arabinose also occur, as well as disaccharides such as rutinose. Phenolic compounds act as