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Does 1-MCP Help an Apple Keep the Doctor Away?

There is a growing interest in flavonoids as an integral antioxidant of the human diet, due in part to its demonstrated strong anticarcinogenic activity and inhibition of tumor cell proliferation (1). Apples have been shown to contain high amounts of flavonoids, including anthocyanins, flavonols (e.g. quercetin) and flavan-3-ols (e.g. catechin), and the simple phenol chlorogenic acid (2)(see below). In the North American diet, apples are the largest source of flavonoids, and have the second highest level of antioxidant activity (3). Listed below is a list of the 4 main classes of phenolics found in apple, and some examples of their role in human health and nutrition.

Anthocyanins: The compound responsible for the red pigmentation of apple, it is also an important antioxidant and anticarcinogenic agent. Other good dietary sources of anthocyanins include blueberry, elderberry, red grape, red wine and cherry.

Flavonols: Best represented in apple by the specific compound called quercetin, it is an excellent metal chelator and a strong antioxidant. High levels of quercetin have been correlated with a reduced incidence of various cancers (breast, colon and liver), heart disease (modulation of platelets), and lipid peroxidation. Other good dietary sources of flavonols include broccoli, red onion, kale and teas.

Flavan-3-ols: Also known as tannins or catechins, this group of flavonoids is what makes tea healthy. A powerful antioxidant, it can also inhibit low-density lipoprotein (LDL; a.k.a. “bad cholesterol”) oxidation, and colon cancer. Aside from apple, other good dietary sources of flavan-3-ols include chocolate and red wine.

Chlorogenic acid: A simple phenol (not a flavonoid) with very high peroxyl free radical scavenging capability. Peroxyl radicals have been linked with tumor promotion and carcinogenesis, as well as physically damaging DNA. High levels of chlorogenic acid are also found in coffee (contributes to the upset stomach some people get from drinking too much coffee), tea, potato, cocoa and various fiber sources.

With respect to apple physiology, it is known that both the content of the flavonoids and the production of ethylene increase with harvest maturity, suggesting that the flavonoid pathway may be regulated (whole or in part) by ethylene. This raises concerns that a treatment of 1-methylcyclopropene (1-MCP), a potent inhibitor of ethylene action, may adversely affect the total flavonoid content of the fruit. Neither the commercial harvesting practices, nor a 1-MCP treatment have been investigated for their effect on the flavonoid content in apple. 

The Study: The objective of this study was to determine the effect of a postharvest treatment of 1-MCP on the various nutraceutical compounds and antioxidant scavenging capacity of apple. 

1-MCP Treatment Effect on Nutraceuticals: The 1-MCP treatment resulted in a significant increase in the total amount of flavonoids, with the greatest increase occurring in the red pigment-forming anthocyanin class of flavonoids (Table 1). However, the 1-MCP treatment also resulted in a 25% decrease in the total amount of chlorogenic acid. 

Total Antioxidant Capacity: Using the TOSC assay (a test to determine the total antioxidant capacity of a given tissue; TAC), it was found that red ‘Delicious’ had the highest level of antioxidants, with ‘Empire’ having the least, and ‘McIntosh’ tissues being intermediary (Table 2). However, in all cases, a treatment of 1-MCP resulted in a higher level of antioxidants during storage than in the non-treated control.

In general, for red ‘Delicious’ it appears that a 1-MCP treatment will result in a slightly higher level of flavonoids (+5%), and total antioxidant capacity (+3%), but with a rather large reduction in chlorogenic acid levels (-25%). This reduction in chlorogenic acid in 1-MCP treated fruit is only seen in early harvested fruit, and is likely due to the inhibition of chlorogenic acid synthesis in the ripening fruit by the 1-MCP. Although a late harvest would result in a higher level of flavonoids and chlorogenic acid by minimizing this inhibition, it would unfortunately also result in a loss of the beneficial effects of the 1-MCP treatment, such as firmness retention and inhibition of ethylene perception. In conclusion, the overall net effect of a treatment of 1-MCP on apple nutraceutical compounds appears to be of benefit for human health and nutrition.

1. Rice-Evans, C.A., Miller, N.J., Paganga, G. (1996). Free Rad. Biol. Med. 20:933-956.
2. Oleszek, W., Lee, C.Y., Jaworski, A.W., Price, K.R. (1988). J. Agric. Food Chem. 36: 430-432.
3. Boyer, J., Liu, R.H. (2004). Nutr. J. 3: 5-20.
4. MacLean, D., Murr, D.P., DeEll, J.R. Horvath, C.R.(2006). J. Agric. Food Chem. 54: 870-878.
5. MacLean, D., Murr, D.P., DeEll, J.R. (2003). Postharvest Biol. Technol. 29: 183-194.

Acknowledgement - This research was supported by OMAFRA, AAFC, Agrofresh Inc., Ontario Apple Growers, and Lingwood Farms.

Table 1. The total flavonoid and chlorogenic acid contents of red ‘Delicious’ apple over all cold storage removals (0, 30, 60, 90 and 120 d), harvest maturities (-7, 0 and +7 d) and shelf-life periods (+1 and +8 d)(μg g^-1 f.w.)

^a No, Yes; not significant and significant at P<0.001, respectively. Modified from (4)

Table 2. The effects of 1-MCP on the antioxidant capacity of four apple tissues after 120 d of 0ºC storage (ŋmoles Trolox Equivalents g^-1)

Yes is significant and significant at P<0.01. Modified from (5)