For a long time, people believed that washing fresh food and vegetables could reduce the possibility of food poisoning before eating fresh fruits and vegetables. However, researchers recently pointed out that cleaning and even the use of chlorine-containing disinfectants to wash fruits and vegetables may not protect people's health.
The reason for this point of view is that studies have shown that certain microorganisms that can cause diseases are experts in playing hide-and-seek games with chemical disinfectants. These bacteria can hide in lettuce, spinach and other vegetable leaves and fruits, and people often use vegetables and fruit surface cleaning methods to endanger them. What is more, some bacteria can also be sorted out and organized on a large scale, forming a dense “group†called biofilms that cover the skin of vegetables and fruits to protect themselves from infringement. This biofilm can protect bacteria that cause a variety of diseases, such as Salmonella and E. coli.
In the past 10 years, the consumption of fresh vegetables and fruits in the United States has increased year by year. However, unfortunately, as the consumption of vegetables and fruits increases, the number of people who get sick due to infections such as E. coli is also increasing. Fresh vegetables and fruits are usually grown in open fields, where they may be exposed to pathogens such as land, irrigation water, manure, and wildlife, and there is a danger of bacterial contamination.
Dr. Brandon Niemilla, a microbiologist at the US Department of Agriculture’s Agricultural Research Service, said that the outbreak of spinach outbreaks in the United States in the fall of 2006 has raised questions about why microorganisms can survive after being cleaned. At the time, studies showed that pathogens like Salmonella and E. coli could be brought close to fruit after they were formed, and they could be transferred to fruit during plant growth and maturation, such as pollination or watering of plants.
The food irradiation method is to expose the food to an electron beam source capable of generating positive and negative charges. It can disintegrate the genetic material of living cells in the food, thereby inactivating parasites in the food and killing pathogens and pests. . Thus, under the leadership of Nihemila, researchers began to understand whether the irradiation method could effectively kill microorganisms that entered the fruit or leaves.
To understand how the bacteria in the leaves responded to different treatments, Niemmila and colleagues designed ways to “inject†bacteria into green leafy vegetables. They cut lettuce and spinach leaves into small pieces and then dipped them into E. coli-containing liquids. Using a vacuum infusion technique, they send the bacteria into small pieces of leaves, which are then either washed with water for 3 minutes, or chemically treated for 3 minutes, or irradiated.
After the above treatment, the researchers suspended the leaflets in a neutral buffer solution and smashed the leaves to obtain and count the number of bacteria therein. The results showed that the use of water washing methods can not effectively reduce the bacteria in spinach or lettuce leaves; using chemical methods of sodium hypochlorite solution can not effectively reduce E. coli in spinach leaves, but the reduction rate of bacteria in lettuce leaves nearly 90%%; The situation of ionizing radiation is quite the opposite. Both lettuce and spinach have a large reduction in the number of bacteria in their leaves. Experiments show that the amount of bacteria reduction is related to the measurement of irradiation. In the case of high metering, the amount of bacteria in lettuce leaves was reduced by 99.99%, and in spinach by 99.9%.
Immediately, the researchers conducted irradiation experiments with biofilm-protected Salmonella and E. coli. Nihemila said that Salmonella hiding in biofilms is easier to kill than E. coli. At present, researchers are studying the protective effect of biofilms on multi-leaf green vegetables in order to understand how irradiation methods can effectively kill bacteria.
Nihemila said: “Whether they are hiding in the leaves or inside the biofilm, they are not easily killed when the bacteria are protected. This is the first time people have studied the use of irradiation methods to stay in the leaves or hide in the biofilm. The bacteria in it," he said, it is unclear whether human pathogens can proliferate in plant tissues. He thinks this is a very important issue, because if pathogens cannot effectively proliferate in the protected space but only stay within a small amount, they will not be too harmful to consumers; if they can Proliferation, their degree of danger will greatly increase.
Nihemila said that the use of irradiation technology to treat fresh vegetables and fruits can effectively kill pathogens lurking in vegetables and fruits, and it is expected to reduce the number of Americans who suffer from food problems each year. The research team he led suggested to the government that the application of irradiation methods in fruits and vegetables should be promoted. Currently, the U.S. Drug and Food Administration is reviewing this method of treating food with radiation.
Dr. Christian Brun, an expert on consumer food safety and quality at the University of California, said that although some militant groups oppose the treatment of food irradiation, due to years of studies showing that irradiation is a way to effectively reduce foodborne diseases, consumers The confidence in the method has gradually increased. She said that after being informed of the benefits of radiation treatment and its acceptance from health agencies, 60% to 90% of consumers said they would purchase irradiated food.