**5.1 Light irradiation and its effective use for enhancing anthocyanin accumulation**

Development of redness in apple fruit peel requires light [22, 23], and the amount of anthocyanin synthesized is correlated with the light intensity received [24]. Therefore, redness development in apple fruit peel is higher on the side that receives more exposure to light (the blushed side) than on the shaded side (**Figure 1**). Hamadziripi et al. [25] revealed the effects of microclimate at different positions in the apple tree canopy "Starking" on peel redness and anthocyanin concentration. They found that the outer-canopy fruits were redder and contained more anthocyanins than the inner-canopy fruits. This seemed to be related to microclimatic differences in irradiance, because outer-canopy fruits were exposed to almost 30 times the irradiance *Anthocyanins in Apple Fruit and Their Regulation for Health Benefits DOI: http://dx.doi.org/10.5772/intechopen.85257*

**Figure 1.**

*Occurrence of anthocyanins in "Fuji" apple peel on the blushed side (the right side in this photo), which receives more exposure to sunlight.*

as fruits in the innermost portion of the canopy, and the average peel temperature of outer-canopy fruits was about 10°C higher than that of the inner-canopy fruits. In addition, among the eight "Gala" strains mentioned in Sections 2.3 and 4, the anthocyanin concentration on the blushed side was about three to five times that on the opposite shaded side at commercial harvest and after the harvest in low- and mediumhigh-coloring "Gala" strains [17]. Apparent differences in anthocyanin concentrations between the blushed and shaded sides of "Gala" apple peel occur near maturation (125 days from flowering), when the anthocyanin concentration increases markedly only on the blushed side [19].

To enhance peel color, cultivation techniques that are effective in promoting anthocyanin synthesis and improving color in apple peels have been developed. In red-skinned cultivars, to allow the apple skin to receive more exposure to light and thereby promote redness, the leaves covering fruits are removed before harvest [5]. Rotating the fruit and branch management such as pruning and putting support posts beneath the canopy can also improve the redness of apple peel [5]. Placing reflective films on the ground also effectively increases the intensity of light entering the apple tree canopy (**Figure 2**) [26, 27]. Ju et al. [27] reported that, after film application, the light intensity inside the tree canopy "Fuji" increased from 30% of daylight to 50–68% of daylight for foil film (crinkled aluminum foil bonded onto cloth) and metalized film (aluminum metalized polypropylene film); the anthocyanin concentration and percent redness of the fruit peel at harvest were also increased.

Anthocyanin synthesis in apple fruit is highly dependent on light quality, such as ultraviolet-B (UVB) and visible light (e.g., red, blue, and white fluorescent light). UVB and white fluorescent light are essential for anthocyanin accumulation, regardless of the temperature, but white fluorescent light alone does not increase anthocyanin concentration [23]. Anthocyanin synthesis is stimulated more by irradiation with UVB with an emission peak at a wavelength of 312 nm (UVB312) than by UVB353 [28]. UVB312 is more effective in stimulating anthocyanin production

**Figure 2.**

*Reflective material laid on the soil surface between tree rows in a "Fuji" apple orchard to enhance the trees' interception of sunlight.*

than red or blue light. Simultaneous irradiation with UVB312 and red light [28] or UVB312 and white fluorescent light [29] produces much higher anthocyanin than irradiation with either light alone. This synergism seems to have an important role in development of the desirable red peel under field light conditions.
