Chen Zongqi, Academician of the Chinese Academy of Engineering, Honorary Chairman of the China Tea Association
Recently, the problem of aflatoxins in Pu'er tea has aroused people’s great concern about the tea industry. As for this issue, academician Chen Zongxi wrote an article.
I went to Jiangxi on a business trip in a few days ago and saw a hot topic about the problem of aflatoxins in Pu'er tea on the internet. And it was in the heated discussion by many people. I will talk about it in three points and apologized for replying lately, due to busy work.
From the scientific point of view, I think that Pu'er tea is not a suitable substrate for Aspergillus flavus under normal conditions
The Pu'er tea can not be produced aflatoxin under normal condition, because each creature has its environment. Aspergillus prefers to grow, multiply and form toxins in substances containing a certain amount of fat and protein. Pu'er tea is an agricultural product with low fat and protein content. It’s processing process is roughly from breeding fresh leaves (species with large leaf), picking, rubbing, drying, piling, inoculating golden flower fungus artificially or inoculating naturally (natural inoculation), adding water to moist, drying again( Pu'er in bulk) and suppressing. The more detail is that after the fresh leaves are dried and piled up, they are artificially inoculated or naturally inoculated with the golden flower bacteria. In this case, the golden flower fungus becomes a dominant species, and other microorganisms are difficult to grow under such conditions. Besides, the tea polyphenolic compounded in tea has an inhibitory effect on the growth and production of aflatoxins, which has been confirmed by many Chinese and foreign scientists (Muto et al., 2001; Xu Dan et al., 2005; Zhang Hao et al., 2014). ).
Therefore, the component of Pu'er tea can not be considered as a suitable substrate for Aspergillus flavus. But under some extreme environment or bad conditions of storage (such as excessive humidity, etc.), the possibility of growth and reproduction of Aspergillus flavus on Pu'er tea cannot be entirely excluded.
The problem about the content of aflatoxin in Pu'er tea
According to the data published by Chinese and foreign scientists, there are aflatoxins and toxins formed in Pu'er tea, including the great toxic B1 toxin. I have reference to the information published in recent years. In foreign countries, scientists from India, Iran, Austria, Germany, and other countries have analyzed 209 samples in Pu'er tea, which are mainly produced in China. The results showed that there were 23 samples in positive, accounting for 11% in the samples. And there were 9 samples of tea with the content of B1 over 5μg/kg, accounting for 4.3% in the samples. China has not formulated and promulgated the standard of allowable residue for aflatoxins in tea. At present, the standard of corn and peanut in MRL is 20μg/kg. The standard of the rice, wheat, and seasoning is 10μg/kg, 5μg/kg and 5μg/kg. Now I use the most stringent standard of 5μg/kg for this discussion.
In domestic, 452 Pu'er tea samples measured by 6 units including the Oil Crop Research Institute of the Chinese Academy of Agricultural Sciences, Yunnan Agricultural University, Guangdong Center for Disease Control and Prevention, Yunnan Dali Quality Inspection Center, Guangdong Zhongshan Quality Control Center, and Hunan Agricultural University. There were 42 samples with aflatoxin, accounting for 9.3% of the total number in samples. And the content of the aflatoxin in 17 tea samples was higher than 5μg/kg, accounting for 3.8% of the total number in samples. It must be pointed out that in the published datum, some samples were artificially inoculated with Aspergillus flavus to verify whether the aflatoxins could grow in Pu'er tea. The aflatoxins in these samples were not produced under natural conditions, which is also counted in this article.
The above results indicate that the incidence rate of aflatoxin in Pu'er tea by detection in China is very low and its concentration is not high.
The problem about the drinker’s safety in Pu'er tea with aflatoxins
The key to judging how much aflatoxin enters the body when drinking tea is scientifically in terms of the amount of intake. The amount of aflatoxin ingested in the body between drinking tea and eating food are different. When people consume rice, vegetables, meat, fish, eggs, and fruits, these foods enter the human body from the mouth. Therefore, if there are pollutants in these foods, they may also be ingested along with the food. But when drinking tea, people only drink brewed tea and tea does not take into the body. Therefore, the amount of aflatoxin ingested by the human body through drinking tea should consider the following three factors, including the residual amount of aflatoxin B1 in tea, the solubility of aflatoxin in water and the amount of aflatoxin in consumption.
My evaluation plan is like this. The highest standard value of aflatoxin B1 in China's test is 16.1μg/kg(Zhongshan Zhongshan Quality Inspection Center, 2017), and I took this content of aflatoxin B1 in Pu'er tea as a standard in the case. And I took twice the consumption of the world in Pu'er tea as a standard in the calculation, which is 13g/day x 2 times = 26g. Pu'er tea will be consumed more when it is brewed, so I used the double quantity. Aflatoxin B1 is substantially insoluble in water. The literature reports that its solubility in water is 100 mg / L (that is, 100 parts per million). According to similar solubility compounds, the leaching rate of aflatoxin in Pu'er tea does not exceed 10%-15%. Thus, the amount of aflatoxin ingested daily by drinking Pu'er tea is 0.042 - 0.063μg(16.1μg/kg x 0.026 kg x 10% (or 15%) = 0.042 - 0.063μg)
Regarding the risk of the carcinogenic aflatoxin in the drinking of Pu'er tea, the research on description of risk in aflatoxin conducted at home and abroad mostly uses the method of quantitative calculation in excess risk (Joint FAO/WHO Expert Committee on Food Additives. WHO Technical Report Series, 1999, 884: 45-46.). According to the extremely conservative assumption (all people in China are high-spending in Pu'er tea, and the tea they drink is highly contaminated with aflatoxin), only 3.2 of 10 million people will induce Hepatocellular carcinoma, malignant tumors(448 of 1.4 billion people will get it), due to drinking Pu'er tea. So it can be concluded that the risk of cancer caused by aflatoxin in Pu'er tea is extremely low. China has been drunk Pu'er tea for thousands of years. There is no report of an increased incidence of liver cancer in Yunnan Province, which has much consumption of Pu'er tea. This is the most reliable epidemiological survey.
Therefore, the aflatoxin in Pu'er tea can be sure of safety to the people health.