Effects of variety and ripening on apple phytochemicals

Varietal differences

Researchers in our lab have found distinct differences in total phenolic and total flavonoid content between different apple varieties. Of four common varieties used for applesauce (Rome Beauty, Idared, Cortland, and Golden Delicious), Rome Beauty had the highest phenolic content while Cortland apples had the lowest [31]. Rome Beauty apples also had the highest flavonoid content while Cortland apples had the lowest. However, Idared contained much higher anthocyanins than any of the other varieties [31]. Anthocyanins are the antioxidant compounds in the fruits that may give fruit a red or blue color. Out of 10 varieties commonly consumed in the US, Fuji apples had the highest total phenolic and total flavonoid compounds (Figures 3 and 4). Red Delicious apples were also quite high, and the apples containing the lowest amounts of phenolics and flavonoids were the Empire apples and the NY647 apple. Antioxidant activity of apples also differs between different varieties, and was positively associated with the level of total phenolic content. The apple varieties with the higher phenolics tended to have higher antioxidant activity.Researchers have found similar variations in phytochemical content between different cultivars of apples. Van der Sluis et al (2001) found that Jonagold apples contained the highest concentration of quercetin glycosides, catechins, and chlorogenic acid when compared to Golden Delicious, Cox's Orange, and Elstar apples. Golden Delicious had the second highest concentration, while Cox's Orange and Elstar had the lowest concentrations [72]. Escarpa and Gonzalez (1998) found that Golden Delicious had the lowest concentration of flavonoids when compared to Reinata, Red Delicious, and Granny Smith apples. Reinata had the highest level of flavonoids, followed by Granny Smith and Red Delicious varieties. Another group looked solely at procyanidin content of four varieties of apples and found that Granny Smith and Red Delicious had the highest procyanidins while McIntosh and Golden Delicious had the lowest [73].

Growth conditions

Besides variety of apple, factors such as development and ripening of the fruits may impact phytochemical profiles in apples. Quercetin glycosides, phloridzin, catechins, and chlorogenic acid concentrations in Jonagold and Elstar apples were highest early in the season, and decreased to a steady level during maturation and ripening [74]. Anthocyanins in Elstar and Jonagold apples started high and decreased in mid-season, but rose rapidly just prior to maturation. Interestingly, this increase in anthocyanin content occurred only in fruits grown in the outer part of the canopy, and not in those grown in the inner part of the canopy. The amounts of quercetin glycosides in both Jonagold and Elstar were also greater in fruit grown in the outer canopy [75]. Awad (2000) also found that sun exposed fruits (both Jonagold and Elstar) had greater levels of anthocyanins and quercetin glycosides when compared to the shaded fruits, giving more evidence that exposure to sunlight affects these two compounds production [76]. In general, it can be concluded that improving light exposure for apples may help increase the production of certain phytochemicals. There was no sunlight effect on phloridzin, catechin, and chlorogenic acid.

Plant nutrition

The effect of different nutrients on flavonoids and chlorogenic acid in apples has also been examined. Awad (2002) found that nitrogen fertilization was associated with decreases in anthocyanins, catechins and total flavonoids, and also with decreased percentage of blush in the fruit peels. In Elstar apples, calcium fertilization was associated with an increase in anthocyanins and total flavonoids [77]. They also examined the effects of applications of different chemicals that may enhance ripening on the formation of different phytochemicals. Ethephon increased anthocyanin production, but did not increase chlorogenic acid or any of the other phytochemicals studied. Gibberellins and (s)-trans-2-amino-4-(2-aminoethoxy)-3-butenoic acid hydrochloride (ABG-3168) both decreased anthocyanin production, but did not have an effect on other compounds studied. The application of other chemicals, such as alar, cycocel, seniphos, shikimic acid, plantacur-E and galactose did not have an effect on any of the phytochemicals examined [77,78].