Food contamination by mold and its toxins and its prevention

作者：admin  点击次数：22  发布时间：2025-04-01

(I) Overview of molds and mycotoxins Most molds closely related to food hygiene belong to the genera Aspergillus Micheli, Penicillium and Fusarium in the class Fungiimper/ecti. In addition, common molds in food include Mucor, Rhizopus, Trichoderma, Alermaria and Cladosporium. Mycotoxin mainly refers to the toxic metabolites produced by molds in the contaminated food.
1. Characteristics of mold toxin production
(1) Mold toxin production is limited to a few toxin-producing molds, and only a part of the strains of toxin-producing species produce toxins. As for the existence of strains with different toxin-producing abilities in the same species, it may be due to the biological characteristics of the strain itself, different external conditions, or both.
(2) The toxin-producing ability of the same toxin-producing strain is variable and changeable. For example, toxin-producing strains can completely lose their toxin-producing ability after repeated generations of culture, while non-toxin-producing strains can develop toxin-producing ability under certain conditions. (3) The mycotoxins produced by toxin-producing strains are not strictly specific, that is, one species or strain can produce several different toxins, and the same mycotoxin can also be produced by several molds. For example, Aspergillus versicolor can produce aflatoxin and Aspergillus nidulans, and Penicillium insularis can produce yellow Tianjing, red Tianjing, Penicillium insularis and cyclochlorine.
(4) Toxin-producing molds require certain conditions to produce toxins. Mold contamination of food and reproduction on food are prerequisites for toxin production, and whether mold can reproduce on food is related to the type of food and environmental factors.
2. Conditions for mold toxin production The so-called toxin production conditions mainly refer to the substrate (food), moisture, temperature, air circulation and other conditions. (1) Substrate Molds are easier to reproduce on natural food than on artificial synthetic culture media. The molds found in various foods are mainly of certain species. For example, the detection rate of Aspergillus flavus and its toxins is high in corn and peanuts, Fusarium and its toxins are the main contamination in wheat and corn, and Penicillium and its toxins are mainly found in rice.
(2) Moisture The moisture content in food is an important factor affecting the microbial phase and its proliferation as well as food spoilage. However, it is not the total moisture content in the food that plays a role in this regard, but only the part of the moisture that can be used by microorganisms, which can be measured by water activity (A_). The smaller the A value of the food, the less moisture it can provide for the growth of microorganisms, and the less conducive it is to the reproduction of microorganisms. For grains, when A drops below 0.7, general molds cannot grow.
(3) Humidity Different molds are prone to reproduction at different relative humidities. For example, when the relative humidity is below 80%, dry molds (gray green koji, limited green koji, white koji) mainly reproduce; when the relative humidity is 80%~90%, mesophytic molds (most koji, penicillium, fusarium) mainly reproduce; and when the relative humidity is above 90%, wet molds (Mucor, yeast) mainly reproduce. Generally, in a non-sealed state, the moisture in the grain and the relative humidity of the environment can gradually reach a balance. When the relative humidity is 70%, the grain reaches the condition of balanced moisture, and the mold cannot produce toxins.
(4) Temperature The external temperature also has an important influence on the reproduction and production of molds. The most suitable temperature for the reproduction of most molds is 25~30℃. When it is below 0℃ or above 30℃, it cannot produce toxins or its ability to produce toxins is weakened.
(5) Ventilation Most molds require aerobic conditions for reproduction and toxin production, but Mucor and Qingqing Green Aspergillus are anaerobic bacteria and can tolerate high concentrations of CO.
3. Main toxin-producing molds and main mycotoxins
The main toxin-producing molds known at present are:
(1) Aspergillus genus includes Aspergillus flavus, Aspergillus ochraceus, Aspergillus versicolor, Aspergillus fumigatus, Aspergillus nidulans and Aspergillus parasiticus.
(2) Penicillium genus includes Penicillium islandicum), Penicillium ucirinum, Penicillium cireoviride, Penicillium expansum, Penicillium cyclopium, Penicillium nugulosum, and Penicillium unicae. (3) Fusarium includes Fusarium poae, F. sporotri-chioides, F. tricincturn, F. nivale, F. ro-seum, and F. graminearum.
(4) Other genera such as Trichoderma viride, Myrothecium loda, and Slachybotus corda) etc.
There are about 200 known mycotoxins. The more important ones are aflatoxin, ochratoxin, sterigmatotoxin, penicillin, huangtianjing, cyclooxygenase, patulin, penicillin, rugose penicillin, penicillin acid, arc penicillin, dihydronivalenone, F-2 toxin, T-2 toxin, etc. Since a toxin may show multiple toxicities, and the toxic effects of mycotoxins on the human body have not been fully clarified, it is still advocated to classify mycotoxins according to the source of toxin production.
4. The food hygiene significance of mold and mycotoxins When mold and mycotoxins contaminate food, two aspects should be considered from the perspective of food hygiene: (1) Mold contamination causes food spoilage After mold initially contaminates food, when the substrate and environmental conditions are suitable, the food will first become spoiled. This will not only cause the food to have an unusual color and produce musty odors, reduce its edible value, or even make it completely inedible, but also reduce the quality of the processing technology of the food raw materials, such as the flour yield, rice yield, and viscosity. The losses caused by mold contamination of grains and their products are the most serious. It is estimated that at least 2% of the world's grain is inedible due to mold contamination each year. The degree of mold contamination of food and the hygienic quality of contaminated food can be assessed from two aspects: the degree of mold contamination and the composition of mold phases. (2) Mycotoxins cause human and animal poisoning. As early as the 19th century, there were reports of ergot poisoning caused by eating flour in humans. In the 1960s, it was discovered that feed contaminated with Aspergillus flavus and containing aflatoxin caused livestock and poultry poisoning. From the perspective of the occurrence of mycotoxin poisoning, there is no infectious epidemic, so it can be distinguished from infectious diseases. The massive growth and reproduction of fungi and the production of toxins are the prerequisites for mycotoxin poisoning, which requires certain conditions, especially temperature, humidity, the consumption of foods that are prone to poisoning in the population, and eating habits, so mycotoxin poisoning can show obvious locality and seasonality, and some can even have the characteristics of endemic diseases.
The clinical symptoms of mycotoxin poisoning are varied and complex. There are acute poisoning caused by eating a large amount of mycotoxins in a short period of time, and there are also chronic poisoning caused by eating a small amount of food containing mycotoxins for a long time, which manifests as inducing tumors, causing fetal malformations and causing mutations in genetic material in the body.