DEAR DR. BLONZ: During a recent online nutrition class, there was a discussion about whether fruits and berries have the most antioxidants, and other beneficial substances, when they are the sweetest. This was the position taken by the teacher and supported by some students, but I argued the opposite. Who is correct? -- P.E., Chicago
DEAR P.E.: You have my support. The “mission” in the plant world, if we can think of it like that, is to grow and reproduce to propagate the species. Unlike animals, plants can’t get up and run away from dangers. Successful plants have evolved to resist threats from limited resources, insects, microorganisms and animals, to name a few. The environment is also a player. A report in the February 2020 issue of the National Academy of Sciences’ journal reported that unchecked global warming might contribute to the extinction of up to one-third of all plant species by 2070.
Successful plants have evolved to create physical and chemical protections to facilitate their growth and the development of seeds needed for reproduction. Chemicals produced by plants (phytochemicals) represent an in-house tool kit for defense and repairs.
Where do antioxidants fit in the picture? From the moment its first shoot emerges, a plant relies on the sun for energy. Too much radiation from the sun, however, can result in oxidative damage to plant tissues. Fruits and vegetables make antioxidants as protection against destructive oxidation. These antioxidants are for the plant’s protection, not ours.
Another side of the story involves seed distribution. The wind can serve that purpose; in those instances, seeds are light in weight and designed for flight. Some seeds get distributed through barbs, which get them carried away on animal fur. Other seeds develop inside fleshy fruit that gets consumed by animals, passes through the digestive system and is then deposited in a new location.
Of relevance to your class discussion is that the protective phytochemicals are at their peak before the seed is ripe. The plant’s entire resource investment is near its conclusion. The last thing the plant needs is an animal feeding on the fruit before the seed is ready for the dance. Unripe fruits don’t taste great -- that’s the way it should be -- and antioxidants contribute via their bitter, astringent or acidic tastes.
Once the seed is ripe, however, the goal shifts to facilitating seed distribution. Sweetness develops when “unsweet” complex carbohydrates get broken into simple sugars -- usually fructose, which is about 1.4 times as sweet as sucrose. Along with that come changes in color and odor: all signals to animals that dinner is served.
You can see, and hopefully explain to the class, that a piece of fruit harvested before it reaches its peak ripeness can, of course, be less sweet. But less sweetness doesn’t necessarily mean smaller amounts of beneficial substances.
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