Quality Analysis of Five Edible Wild Vegetables in Chongqing

Huan MA Huihe LI

Abstract [Objectives] This study was conducted to analyze the quality of several kinds of wild vegetables in Yongchuan District， Chongqing City.

[Methods]Five common edible wild herbs， Plantago asiatica， Taraxacum mongolicum， Pteridium aquilinum （L.） Kuhn var. latiusculum （Desv.） Underw.ex Heller， Brasenia schreberi and Houttuynia cordata in Yongchuan District， Chongqing， were tested for nitrate， amino acid， reducing sugar， and vitamin C contents.

[Results] The vitamin C content was the highest in B. schreberi， reaching 1 056 mg/kg， and the lowest in P. aquilinum var. latiusculum， at only 61 mg/kg. T. mongolicum had the highest reducing sugar （E value） and amino acid contents， at 1.01 and 24.3 mg/kg， respectively， and the values were the lowest in P. asiatica， at 0.15 and 9.1 mg/kg， respectively; and the nitrate contents ranked as H. cordata （2 529 mg/kg）﹥B. schreberi （2 188 mg/kg）﹥P. aquilinum var. latiusculum （1 900 mg/kg）﹥P. asiatica （1 097 mg/kg）﹥T. mongolicum （1 079 mg/kg）， which were at the level of medium to high pollution， but within the scope of the national acceptable daily intake （ADI）. The nutritional value of wild vegetables is higher than that of vegetables grown in the field， but some wild vegetables are also toxic， which will have adverse effects on human health.

[Conclusions]People need to develop and utilize wild vegetable resources scientifically and rationally according to their own needs.

Key words Wild vegetable; Vitamin C; Amino acid; Nitrate

Received： February 27， 2021  Accepted： April 23， 2021

Huan MA （1985-）.Female，P.R. China，devoted to research about  biotechnology.

*Corresponding  author E-mail： lihuihe@163.com

Wild vegetables refer to wild or semi-wild plants that grow naturally in the wild without artificial cultivation and whose roots， stems， leaves or flowers and fruits can be used as vegetables[1]. Because there is no industrial pollution in the environment where wild vegetables grow， and no chemical fertilizers or chemical pesticides are used， wild vegetables have unique flavors such as freshness， mellowness and aroma， and most wild vegetables also have extremely high medicinal value and corresponding health care effects， and are nutritious green food with multiple functions. Wild vegetables are favored by people because of their high nutrition， high medical and health effects and pollution-free quality， and are called "healthy food"[2]. In recent years， peoples diets tend to pollution-free and green foods， and the consumption of wild vegetables has quietly risen at home and abroad. Modern people are eager for wild foods that "return to nature". Wild foods have become the latest focus of peoples attention with their huge numbers， rich genetic diversity， outstanding resistance and adaptability， and significant therapeutic value. Therefore， the quality analysis of various wild vegetables is an important measure to ensure the safety of peoples consumption.

Materials and Methods

Experimental materials

Taraxacum mongolicum， Houttuynia cordata， Pteridium aquilinum （L.） Kuhn var. latiusculum （Desv.） Underw.ex Heller， Brsenia schreberi， and Plantago asiatica L. were all collected from the cucumber hillside of the Xinghu Campus， Chongqing University of Arts and Sciences， in the most suitable edible period.

Experimental and analysis methods

The soil and debris on the five collected wild vegetables were washed with clean water， and the excess water on the surface was wiped off with a clean towel. The wild vegetables were stood for 1-2 h to allow the evaporation of excessive moisture. For the quality indexes， the Vc content was determined by the 2，6-dichloroindophenol method[3]; the reducing sugar content was determined by the 3，5-dinitrosalicylic acid method[4]; the nitrate content was determined by the ultraviolet spectrophotometric method[5]; and the amino acid content was determined by the ninhydrin hydrate method[6].

Results and Analysis

Reducing sugar contents of wild vegetables

It can be seen from Table 1 that the reducing sugar content was the highest in T. mongolicum among the several common wild vegetables in Xinghu campus， and the value was 6 times of those in P. aquilinum var. latiusculum and P. asiatica， 4 times of that in H. cordata， 3 times of that in B. schreberi， showing an order of B. schreberi>H. cordata>P. aquilinum var. latiusculum>P. asiatica. It is recommended that people with diabetes should eat less T. mongolicum， so as not to increase blood sugar.

Nitrate contents of wild vegetables

The nitrate contents of common wild vegetables ranked from high to low as H. cordata>B. schreberi>P. aquilinum var. latiusculum>P. asiatica>T. mongolicum. According to the standards of the World Health Organization and the United Nations Food and Agriculture Organization： the ADI value （daily allowable amount） of nitrate is 3.6 mg/kg body weight[7]， and if the weight of Chinese nationals is 60 kg， the daily allowable amount per person will be 216 mg. If the amount of vegetables eaten by a person is 0.5 kg per day， the allowable amount of nitrate per kilogram of vegetables will be 432 mg. If the amount of nitrate loss during washing， blanching and cooking is included， the allowable amount of nitrate per kilogram of vegetables can be expanded to 1 500-2 000 mg. Although nitrate itself is harmless or relatively low toxic to the human body， modern medicine proves that the nitrate ingested by the human body can be reduced to nitrite under the action of bacteria， and nitrite can reduce the oxygen carrying capacity of the blood， thus leading to methemoglobinemia， especially in infants and young children[8]. On the other hand， nitrite can react with secondary amines （secondary amines， tertiary amines， amides and amino acids） in other foods， pharmaceuticals， residual pesticides and other ingredients ingested by humans， forming powerful carcinogens （nitrosamines） in the gastric cavity （pH3）， which further can induce canceration of the digestive system[9]， which poses a potential threat to human health.

Studies have shown that most of the nitrate intake by the human body （70% to 80%） comes from vegetables[10]， which are plant foods that are very easy to accumulate nitrate[11]. Zhou et al.[12] believed that the limit of nitrate concentration for human poisoning was 3 099 mg/kg， so it is not recommended to eat raw P. aquilinum var. latiusculum and P. asiatica. In addition， according to Zhangs grading standard[13] for the nitrate content of wild vegetables， these five wild vegetables have high nitrate content and serious pollution.

Amino acid contents of wild vegetables

It can be seen from the measurement result table that the amino acid content of T. mongolicum was the highest， reaching 24.3 mg/kg， which was significantly higher than other four wild vegetables， so it has great nutritional value. The values of other four wild vegetables were B. schreberi 13.9 mg/kg， P. aquilinum var. latiusculum 13.0 mg/kg， H. cordata 10.3 mg/kg， and P. asiatica 9.1 mg/kg. Amino acids are one of the many biologically active macromolecules that construct biological organisms， and they are the basic materials for constructing cells and repairing tissues. The balance and proper supply of amino acids are the basic prerequisites for human health. The lack of any kind of amino acid supply will affect the performance of the immune system and other normal functions， making people in a sub-healthy state and becoming more vulnerable to diseases.

Vitamin C contents of wild vegetables

Among the five wild vegetables， B. schreberi had the highest vitamin C content， which was 1 056 mg/kg， followed by 957 mg/kg in H. cordata. From this point， they both are high-quality ideal edible wild vegetables. The vitamin C contents of other three edible wild vegetables， T. mongolicum （278 mg/kg）， P. asiatica （192 mg/kg） and P. aquilinum var. latiusculum （61 mg/kg）， decreased successively. Studies have shown that vitamin C is a good blocking agent for blocking the formation of nitroso compounds both in vivo and in vitro， and when the molar ratio of Vic to nitrite is 2∶ the blocking rate is 100%[11]. Vic can improve immunity， especially for preventing influenza， upper respiratory tract infections and other diseases. Vic also helps to improve the elasticity of blood vessels. It is an antioxidant that can decompose cholesterol into sulfide and excrete it from the body， thereby cleaning blood vessels and facilitating transportation of nutrients and development of the brain.

Conclusions and Discussion

From the comprehensive consideration of food safety and nutritional value， T. mongolicum was the best among these kinds of wild vegetables. Its reducing sugar and amino acid contents were high， and its vitamin C content was in the middle. Although the nitrate content was in the third-level pollution range， it was still in a safe range and could be eaten at ease， because there would be a lot of loss of nitrate during washing and cooking. B. schreberi and H. cordata were the second， because they had relatively high amino acid content， although the reducing sugar content was average. Although their nitrate contents were relatively high， their food safety and nutritional value were ensured， because their Vc contents were also very high， which is beneficial to blocking the conversion into nitrite in the body， and pre-treatment such as blanching before cooking can remove most of the nitrate. Next， P. asiatica and P. aquilinum var. latiusculum had lower nitrate contents than the daily allowable amount， so they are a safer choice for wild vegetables， but their nutritional value is also low.

Although current studies have shown that the nutritional value of wild vegetables is higher than that of vegetables grown in the field， some wild vegetables are still toxic and have adverse effects on human health. Therefore， we must scientifically and rationally develop and utilize wild vegetable resources， and choose wild vegetables that are safe， non-toxic， and high in nutritional value according to different needs.

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