**5.3 Enhancing anthocyanin accumulation through the choice of the nutrient and nutrient level**

Fruit nutrient composition has a strong association with fruit color. In general, nitrogen (N) negatively affects apple fruit redness [32, 33]. The percentages of well-colored fruit of "Jonathan" apples were higher in trees given ammonium nitrate fertilizer at 0–5 g N m<sup>−</sup><sup>2</sup> year<sup>−</sup><sup>1</sup> than in trees given the same fertilizer at higher rates of up to 10–20 g N m<sup>−</sup><sup>2</sup> year<sup>−</sup><sup>1</sup> from 1978 to 1983 (**Figure 3**) [32, 34]. The excessive nitrogen application decreased the redness of the apple peel. Similarly, in "Elshof" (bright red with yellow background color), the anthocyanin concentration and percentage of blush are generally decreased by increasing the amount of N fertilizer [35]. Foliar application of nitrogen by using urea spray lessens the increase in anthocyanin concentration in the blush-side peel of "Gala" apples at maturity [19]. Furthermore, Awad and Jager [35] reported that the anthocyanin concentration in the peel of "Elshof" and "Elstar" (mostly red with yellow showing) apples at maturity is negatively correlated with the concentrations of N and magnesium (Mg) and with the N to calcium (Ca) ratio in the fruit at maturity, but the most important nutrient factor associated with anthocyanin concentration at maturity is the N concentration in the fruit during growth and at maturity. The result obtained from Awad and Jager [35] suggests that the maximum level of anthocyanin concentration in apple fruit peel could be achieved if the N concentration could be maintained at marginal N fertility levels to minimize the N concentration in the fruit.

#### **Figure 3.**

*Effects of N application as ammonium nitrate on the percentage of well-colored "Jonathan" fruit. (A) Percentages of well-colored fruits from 1978 to 1983 in a long-term N fertilization field, Japan. A well-colored fruit is designated as one in which over 80% of the peel is colored. Data are running averages from 3 years ±SD, n = 3. Data are from [34]. (B) Representative fruit from an unfertilized tree (0 g N m<sup>−</sup><sup>2</sup> year<sup>−</sup><sup>1</sup> ; left picture) and a fertilized tree (up to 20 g N m<sup>−</sup><sup>2</sup> year<sup>−</sup><sup>1</sup> as application of ammonium nitrate fertilizer; right picture); the peel of apples from the unfertilized tree is a superior red.*

Anthocyanin synthesis in apple fruit is associated with not only N but also phosphorus (P) and Ca nutrients. P-Ca mixtures with mineral ions, such as Phostrade and Seniphos, have been used widely to enhance fruit coloration. Superior redness

*Anthocyanins in Apple Fruit and Their Regulation for Health Benefits DOI: http://dx.doi.org/10.5772/intechopen.85257*

of fruit and high anthocyanin concentrations could be achieved in "Braeburn" apple fruits with foliar application of Phostrade Ca (23.6% P2O5, 4.3% CaO, and 3% N); this effect was due to the P and Ca, not the N [36]. They showed that the anthocyanin concentration in the peel of treated apples at harvest was 20 times, whereas the concentration in the untreated apple peels (control) at harvest was only 9 times those at 5 weeks earlier of the harvest. Another P-Ca mixture, Seniphos (310 g L<sup>−</sup><sup>1</sup> P2O5, 56 g L<sup>−</sup><sup>1</sup> CaO, and 30 g L<sup>−</sup><sup>1</sup> total N: 1% NO3 and 2% NH3, the Phosyn Ltd. Company (Phosyn PLC, York, UK)) is also used commercially to improve peel color in apples. The positive influence of Seniphos on apple redness has been reported in various cultivars, such as "Starking Delicious" [37, 38] and "Fuji" [39], but it is not effective in "Jonagold" [40]. Gómez-Cordovés [37] showed that application of Seniphos increased the anthocyanin concentration in "Starking Delicious" apple peel over the ripening period and also altered the percentage composition of anthocyanins.

Sucrose can promote reddening of apple peel. Anthocyanin concentrations of peel disks of wax apple fruit (light to dark red, sometimes green) increase in a linear fashion with concentration of sucrose in the culture solution [41].
