Postharvest Enhancement of Phenolic Phytochemicals in Apples for Preservation and Health Benefits - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 345

increase in thermotolerance during hyperthermia to accumulation of heat shock proteins
and phenolic metabolites (Zimmerman and Cohill, 1991). Many phenolics are induced in
response to infection, wounding, nutritional stress, cold stress, and UV irradiation (Rhodes
and Wooltorton, 1978; Beggs et al., 1987; Hahlbrock and Scheel, 1989; Christie et al.,
1994; Dixon et al., 1994; Lois and Buchanan, 1994; Dixon and Paiva, 1995). Phenolics
can function as effective antioxidants by scavenging singlet oxygen and free radicals via
their ability to donate hydrogen from hydroxyl groups positioned around the aromatic ring
(Hertog et al., 1992; Foti et al., 1994; Hertog et al., 1995; Rice-Evans et al., 1995; Jorgensen
et al., 1999). A recent study of antioxidant activity in apples by Lee et al. (2003) found that
flavonoids like quercetin, epicatechin, and procyanidin B 2 rather than vitamin C contributed
significantly to total antioxidant activity (Lee et al., 2003).
In light of the vast array of cellular protective functions phenolics have in plants, it
is not surprising therefore that phenolics have diverse medicinal properties for human
health applications. For example, curcumin from Curcumalonga and Curcumamannga and
rosmarinic acid from Rosmarinusofficinali are used as antioxidants and anti-inflammatory
compounds (Peake et al., 1991; Huang et al., 1992; Jitoe et al., 1992; Masuda and Jitoe,
1994; Osawa et al., 1995; Lim et al., 2001). Also, lithospermic acid from Lithospermum
sp. is used as antigonadotropic agent, proanthocyanidins from cranberry can be used to
treat urinary tract infections, and anethole from Pimpinella anisum is used as an antifungal
agent (Winterhoff et al., 1988; Himejima and Kubo, 1993; Howell et al., 1998; Howell and
Foxman, 2002).
Phenolic phytochemicals have also been found to have potential in the management
of oxidative stress-linked chronic diseases like diabetes, cancer, and cardiovascular dis-
ease (Shetty, 1997, 1999, 2001; Shetty and Labbe, 1998; Shetty and Wahlqvist, 2004; Fig.
16.3). In a study involving Empire apples found phenolics from the apples to have po-
tential cancer chemopreventive activity due to their combined antioxidant and anti-tumor-
promoting activities (Kang et al., 2004). Similarly, an epidemiological study by Knekt
et al. (1997) found that intake of dietary flavanoids showed an inverse association with lung

Excessive serum
glucose
(hyperglycemia)

Glucose metabolism results in free radicals

Chronic inflammatory condition

CVD/hypertension

Alzheimer's

Arthritis

Diabetes

Nephropathy Neuropathy Retinopathy

Fig. 16.3 Oxidative stress-related hyperglycemia and complications.