It’s the strawberry season again. A red strawberry enters your mouth, the sweet and sour juice bursts between your lips and teeth, and the soft and tender pulp "melts" in your mouth. It's so intoxicating! But are the strawberries you eat really washed?Someone has really done some research on how to clean strawberries in the “cleanest” way. The most critical operation: don’t pick the strawberry stems!
The researchers selected 3kg of representative Shuofeng strawberries from supermarkets, fruit shops, and roadside fruit stalls, divided them into 8 portions on average, and conducted the 8 cleaning methods in the chart below to compare the effects of different cleaning methods on pesticide residues in strawberry samples.
Image source: Reference [18]
Image source: Reference [18]
The experimental results showed that there is a clear difference in removing pesticide residues between strawberry stems removed and strawberry stems not removed. Strawberries soaked after removing strawberry stems have relatively higher pesticide residues.
This is because if the stemmed strawberries are soaked in water, residual pesticides will enter the fruit with the water, causing more serious pollution. Moreover, the most recommended cleaning method is to rinse with clean water, then soak in clean water, rice water, light salt water, and baking soda for 5 minutes before rinsing.
Picture: Strawberry stalk Picture source: Photographed by the author
Strawberries are actually a summer fruit
Strawberry is a kind of berry, rich in juice, sweet and sour. I remember that when I was a kid, I could only eat strawberries in the summer, and rarely in the winter. But now I can eat strawberries even in the winter. Some people can't help but have questions:"What season is strawberry?"
In fact, under natural conditions, strawberries are a seasonal fruit in summer. Its most suitable growth temperature is around 20℃. Generally speaking, when the soil temperature is between 15 and 23°C, it is suitable for the growth of strawberry root systems; when the air temperature is between 20 and 25°C, strawberry photosynthesis is best.
Therefore, strawberries cultivated in the open field are generally planted in August to September and picked in May to June of the following year. The weather conditions at this time are most suitable for the growth of strawberries.
The thing is: strawberries are so delicious! Demand really exceeds supply.
In order to let everyone happily show off strawberries in winter, greenhouse strawberry cultivation came into being.
At present, my country ranks first in the world in terms of strawberry planting area and consumption, and almost 90% of strawberry planting is done in greenhouses. For strawberry cultivation in greenhouses, preparations usually start from June to August, and are planted around September. They are picked and put on the market around New Year's Day. The harvest period is as long as three months.
In winter, the outdoor temperature is low, which is not suitable for the growth of strawberries, and there is a risk of freezing to death. Greenhouse planting can artificially control temperature and humidity, pollination and soil conditions to ensure the healthy growth of strawberries. So strawberries changed from a "summer fruit" to a "winter fruit".
Someone said: "Isn't this an out-of-season fruit? Isn't it bad for your health?"
In fact, out-of-season vegetables and fruits are very common now, so there is really no need to worry. Strawberries are quite picky about their growth environment requirements. Temperature, humidity, moisture, light, etc. will all affect the photosynthesis of strawberries, thereby affecting the quality of strawberries.
Strawberries grown in greenhouses can artificially control these conditions to ensure that photosynthesis of strawberries can proceed normally, with good flavor and quality. As for the plant growth regulators that everyone is worried about, normal use is not harmful to the human body, and you can eat them with confidence as long as they are washed clean.
Strawberries are sweeter in winter, it’s true!
Many friends will also find that winter strawberries taste sweeter than summer strawberries. Is this an illusion? Not really!
The sugars in strawberries include sucrose, glucose and fructose, with contents of 0.47g/100g, 1.99g/100g and 2.44g/100g respectively, of which fructose has the highest content. Fructose has a characteristic: the lower the temperature, the sweeter the taste, so strawberries will indeed taste sweeter in winter.
Strawberries are not only delicious, they are also very nutritious
1. Vitamin C
When it comes to eating fruits, what everyone is most concerned about is whether they can supplement vitamin C. The contribution of strawberries is quite large. According to the data in the "Chinese Food Composition Table", every 100 grams of strawberries can provide us with 47mg of vitamin C. However, the vitamin C content of different varieties will vary.
Picture: Vitamin C content of different varieties of strawberries Picture source: References [8, 9]
Eating 100~200g of strawberries every day can basically meet the general population’s demand for vitamin C.
Picture: Half a palm-sized strawberry, about 25g. Picture source: Photographed by the author
2. Dietary fiber
The insoluble dietary fiber content of strawberries is 1.1g/100g, and the total dietary fiber content is 2g/100g. There are slight differences in different varieties.
Picture: Dietary fiber content of different varieties of strawberries Picture source: Reference [10]
3. Mineral Potassium
Although the potassium content of strawberries is not as good as that of bananas, it is 1.6 times that of apples, at 131mg/100g, which is beneficial to maintaining healthy blood pressure.
4. Antioxidant ingredients
The content of bioactive substances in strawberries is relatively high, about 2 to 11 times that of common fruits such as apples, citrus, and kiwis. The bioactive ingredients it contains include total phenols, flavonoids, anthocyanins, etc., which have antioxidant and anti-inflammatory effects.
5. Low calories
The calories of strawberries are relatively low among fruits, only 32kcal/100g, which is lower than blueberries, mulberries, apples, pears, peaches, kiwis and other fruits. Even friends who need to control their weight or are losing weight can still enjoy it with confidence.
In addition, a recent study published in "Nutrients" mentioned that long-term consumption of strawberries by middle-aged people can reduce the risk of dementia, but the study used a daily supplement of 130g of strawberry powder.
Don’t believe the rumors about strawberries!
1. Is the strawberry color fading due to dyeing?
No! The skin of strawberries is thin and delicate. A little violence during cleaning may break the tissue of the strawberries, causing the anthocyanins to escape. This ingredient is easily soluble in water, so the water will change color.
2. Are white strawberries genetically modified?
White strawberries are not genetically modified, but are artificially selected varieties. There are currently many varieties of white strawberries, such as Taoxun, Snow Angel, Xiaobai, Snow White, etc.
3. Are hollow strawberries and deformed strawberries injecting hormones?
Strawberry hollowness has nothing to do with hormones, but is related to the variety of strawberry, growth environment, etc.
For example, sweet Charlie and other varieties have low pulp density and are relatively loose in the fruit, which may lead to hollows. Excessive use of nitrogen fertilizer during the fruiting period can also lead to hollows. Sufficient boron is required for internal transportation of the fruit, and a lack of boron will also lead to hollows. Insufficient nutrient supply or harvesting too late can also lead to hollows.
In addition, someone studied the effect of clofenuron on strawberry hollowness and deformity. The results showed that variety is the main factor causing strawberry hollowness, and it is also a factor leading to strawberry deformity. Regardless of whether clofenuron is used during strawberry planting, the risk of hollow fruit deformity will increase as the strawberry size increases.
Summarize:
Strawberries are very nutritious and are normally a seasonal fruit in summer. However, with the development of technology, growing strawberries in greenhouses allows us to happily show off strawberries in winter! When cleaning strawberries, remember to “don’t remove the stems”!
References
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[12] Krikorian, Robert et al. "EarlyIntervention in Cognitive Aging with Strawberry Supplementation." Nutrientsvol.15, 204431.19Oct.2023, doi:10.3390/nu15204431
[13] Wang Lihua. Management technology during critical period of greenhouse strawberry growth in winter [J]. Modern Rural Science and Technology, 2022(2):40-40
[14] In the first half of 2020, the national food safety supervision and sampling inspection pass rate was 97.89% [J]. Food and Life, 2020, (9): 28-29.
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[16] Yu Xia, Cao Junjie, Wang Qianli, Hu Yongjiao, Ran Yan. Research on pesticide residues and heavy metal pollution in strawberries [J]. Guizhou Science, 2023, 41(4): 46-49
[17] Cao Qiumei. Risk assessment and regulatory recommendations for pesticide residues in strawberries [J]. Food Safety Guide, 2021(3):80-80
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[19] Jin Shaoming, Ning Xiao, Gao Wenchao, He Huan, Cao Jin, Ding Hong. Research on the cleaning effect of different cleaning methods on pesticide residues in strawberries [J]. Journal of Food Safety and Quality Inspection, 2017, 8(7): 2549-2554
[20] Cang Tao, Song Wen, Zhao Xueping, Wu Changxing, Wu Shenggan, Chen Liping, Xu Mingfei, Zhao Huiyu, Wang Qiang. Effects of chlorfenuron on strawberry hollowness and deformity [J]. Journal of Zhejiang Agricultural Sciences, 2017, 29(9): 1537-1543
Planning and production
This article is a work of Popular Science China-Starry Sky Project
Produced by Science Popularization Department of China Association for Science and Technology
Producer丨China Science and Technology Press Co., Ltd., Beijing Zhongke Galaxy Culture Media Co., Ltd.
Author丨Xue Qingxin registered nutritionist
Review | Ruan Guangfeng, Deputy Director of Kexin Food and Health Information Exchange Center
Planning | Fu Sijia
Editor丨Fu Sijia