Greenhouse vegetable cultivation makes planting convenient, allowing people to eat vegetables all year round, regardless of the season, which are known as off-season vegetables. But a question arises: are off-season vegetables good for you, and are they safe to eat? "Eat in season" is an old saying that emphasizes eating according to the seasons and what nature provides at a particular time. However, in today's world, we eat watermelon in winter and radishes in summer, and we can hardly tell what's in season anymore. The reason we can get all kinds of fruits and vegetables year-round is that off-season vegetables have become commonplace. Are off-season vegetables safe to eat? How can we choose them to be safer? On these questions that readers are very concerned about, a journalist specially consulted relevant experts for answers.
More than half of the vegetables in the market are off-season
Traditional Chinese Medicine (TCM) places great emphasis on health preservation. Professor Liu Youzhang from the First Affiliated Hospital of Guangzhou University of Chinese Medicine believes: "Follow the laws of nature, and practice health preservation according to the solar terms. Plants and animals are all constrained by climate change. Only by adapting to the four seasons can one be healthy and live a long life. Otherwise, one will inevitably be affected by the heavens and earth and fall ill. In terms of diet, one should of course follow the principle of eating in season and not eat things out of season. One should not violate the way of health preservation for the four seasons just to satisfy one's palate."
So, what is the actual proportion of off-season vegetables in the market today? According to a journalist's investigation, now that it is deep autumn, the market still has summer vegetables like cucumbers, tomatoes, beans, eggplants, bitter gourds, and peppers, as well as spring seasonal vegetables like chives and spinach. A count revealed that more than half of the vegetables are off-season.
It is clear that off-season vegetables are very common in the market. This situation is not only because farmers want to increase production and income, but also a result of the public's demand for a variety of vegetables. For example, red onions are widely planted in the Guangzhou area. They are characterized by high yield, strong onion flavor, and excellent quality, making them an important seasoning vegetable in South China. The normal cultivation time for red onions in the Guangzhou area is from September to March-April of the following year. However, from May to September, the high temperatures and heavy rain greatly affect the open-field production of red onions. At this time, greenhouse-grown off-season red onions become very popular.
Poorer texture, the "Achilles' heel" of off-season vegetables
Careful consumers will notice that although off-season vegetables look good, their texture is slightly inferior when eaten. What's the reason? The high-temperature, high-humidity environment of a greenhouse speeds up the growth of vegetables, making their growth cycle shorter than that of seasonal vegetables grown in the open field. This results in a slightly lower quality and taste compared to seasonal vegetables.
In addition, because of their short growth cycle, off-season vegetables are often treated with ripening agents, which can make their texture worse. For example, the greenhouse tomatoes sold on the market now have very thick skins, and when you bite into them, they feel raw and not fully ripe.
Be wary of excessive pesticide residues in off-season vegetables
Besides poor texture, off-season vegetables have another "Achilles' heel." Compared to seasonal vegetables grown in the open field, off-season vegetables grown in greenhouses suffer from more serious pests and diseases during production due to the high-temperature, high-humidity environment inside the greenhouse, combined with higher planting density. Regarding off-season vegetables, Qian Fengying, who has a master's degree from the Clayton Department of Biological Nutrition in the United States, expresses a cautious attitude in her new book, "Towards Balance—Finding Your Own Health Thinking," suggesting that large-scale cultivation of off-season vegetables may lead to excessive pesticide residues.
In the summer in the south, typhoons, heavy rain, and other severe weather often occur, making vegetable production very difficult and the quality of vegetables low. However, in the high-altitude mountainous areas of northern Guangdong or on plains at different altitudes, adapting to local conditions and using off-season, pollution-free vegetable cultivation techniques can reduce the use of pesticides and fertilizers by 85% and control the nitrate content in vegetables.
Can plant hormones in off-season vegetables cause early puberty in children?
When it comes to off-season fruits and vegetables, many people have heard that they are grown using hormones! Shi Jun, a plant science Ph.D. and a member of the science group "Songshuhui," explains that plant growth hormones, professionally known as "plant growth regulators," are indeed commonly used in cultivating off-season vegetables. This is because when planting in season, pollination in the fields is done by insects like bees. In a greenhouse, such "labor" is not available, so plant growth regulators that can produce fruit without pollination must be used.
All permitted plant hormones undergo long-term toxicological experiments before they are put into practical use. They are almost non-toxic or low-toxic and will degrade. Moreover, they are completely different from the animal hormones that we fear so much.
Some people worry that plant growth regulators for off-season vegetables can cause early puberty in children. In fact, to date, there is no evidence to support this connection. In a 2011 study published in the "Maternal and Child Health Care of China" journal by Du Hongyi and others from the School of Public Health at Fudan University, which investigated the correlation between off-season fruit intake and precocious puberty in girls, data from 105 cases of precocious puberty girls and their off-season fruit consumption were collected. The study ultimately found no association between off-season fruit and precocious puberty in girls.
These regulators have clear scopes of application and dosage requirements. As long as they are used according to these requirements, their safety can be guaranteed.
Therefore, it is even more necessary to apply some techniques to help produce pollution-free off-season vegetables. Generally, pollution-free vegetables should meet the following three conditions:
(1) Pesticide residues do not exceed the standard. Pollution-free vegetables do not contain banned highly toxic pesticides, and the residue levels of other pesticides do not exceed the permissible limits.
(2) Nitrate content does not exceed the standard. The nitrate content in edible vegetables does not exceed the permissible amount, generally controlled below 432 ppm.
(3) Harmful substances such as "three wastes" (industrial waste water, waste gas, and solid waste) do not exceed the standard. Pollution-free vegetables must avoid the harm caused by environmental pollution, and the levels of harmful substances from "three wastes" and pathogenic microorganisms in commercial vegetables must not exceed the permissible limits.
How to choose off-season vegetables safely?
If possible, it is recommended that readers try to choose seasonal vegetables. However, if you have no choice but to eat off-season vegetables, how can you choose them more safely?
1. Expert advice: Consumers should choose vegetables that are normal in size, shape, and color. Don't just pick overly large or brightly colored ones, as this could be the result of improper pesticide use.
2. Smell the vegetables. Most vegetables have fresh, sweet, pungent, or sour aromas. It is not recommended to buy vegetables with any other strange odors.
3. Check the shape. Most vegetables are fresh and normal in appearance. However, some vegetables may grow abnormally due to the use of hormone-like substances.
Finally, it should be reminded that vegetables with insect holes are not necessarily pollution-free. Sometimes, vegetables with insect holes may actually have higher pesticide residues.
How to scientifically wash off-season vegetables?
1. Sunlight exposure
Vegetables and fruits just bought can be placed in the sun for 10 minutes. The multi-spectrum effect of sunlight can help decompose and destroy some of the residual pesticides.
2. Room temperature storage
Storing them at room temperature for about 24 hours will result in an average reduction of 5% in pesticide residues. This method is suitable for melons like winter melon and pumpkin, as well as root and stem vegetables that are easy to store.
3. Soaking and rinsing
Prepare alkaline water by adding 5-10 grams of edible alkali to every 500 ml of clean water. Use enough alkaline water according to the amount of vegetables. Then, place the preliminarily rinsed fruits and vegetables in the alkaline water and soak for 5-15 minutes. Rinse with clean water three more times afterward. For example, for vegetables and fruits with skins like cucumbers and carrots, you can wash them under running water before peeling.
4. Scalding with boiling water
For vegetables like green peppers, cauliflower, beans, and celery, it is best to scald them in boiling water before cooking. This method can remove 90% of the residual pesticides. Discard the scalding water after use.