Detailed introduction of Ochratoxin

Ochratoxin includes 7 compounds with similar structures, the general structural formula: R1=Cl or H; R2=H, CH3 or C2H5. Among them, ochratoxin A (R1=C1, R2=H) is the most toxic, and it is most common in moldy grains and feed.

Ochratoxin is another mycotoxin that has attracted worldwide attention after aflatoxin. It is a group of important food-contaminating mycotoxins produced by 7 species of Aspergillus of the genus Aspergillus and 6 species of Penicillium of the genus Penicillium. Four of them are the most toxic, the most widely distributed, the highest toxin production, and the most harmful to agricultural products. The most polluted and most closely related to human health is ochratoxin A.

Introduction

Ochratoxin A is a colorless crystalline compound. Soluble in polar organic solvents and dilute sodium bicarbonate solution. Slightly soluble in water. Its benzene solvate has a melting point of 94-96°C, and its crystalline melting point in xylene is 169°C. There is optical activity [α]D-118°. The UV absorption spectrum varies with the pH value and the polarity of the solvent. The maximum absorption wavelengths in ethanol solution are 213nm and 332nm. It has high chemical and thermal stability. Ochratoxin A is produced by a variety of Aspergillus and Penicillium that grow on grains (wheat, corn, barley, oats, rye, rice and millet, etc.), peanuts, vegetables (beans) and other crops. After animals have ingested moldy feed, this toxin may also appear in the meat of pigs and hens. Ochratoxin mainly damages animal liver and kidney. This toxin mainly causes kidney damage, and a large amount of toxin may also cause inflammation and necrosis of the animal's intestinal mucosa. Its teratogenic effects have also been observed in animal experiments.

Hamilton et al. (1982) reported a large-scale turkey ochratoxin poisoning for the first time, and it has since been reported in poultry and pig farms in the United States, Canada and European countries. Ochratoxins are a class of compounds produced by a variety of Aspergillus and Penicillium. They are called ochratoxins A (OTA), ochratoxins B (OTB) and ochratoxins C (OTC) in the order of their discovery.

History

In the early 1970s, Penicillium viridicatum was considered to be the main toxin-producing Penicillium fungus of ochratoxin A; after the 1970s, studies such as Natori et al. (1970) and Pitt (1987) showed that most strains of Penicillium verrucosa (P.verrucosum) can produce OTA; a small number of Penicillium purpurescens and P.cyclopium can also produce OTA; and Penicillium verrucosum produces neither OTA nor orange Penicillin (citrinin). The divergence in the understanding of the main toxin-producing Penicillium fungi of ochratoxin may be caused by the different classification methods of fungi used by researchers.

The study of Northolt et al. (1979) showed that the minimum water activity (minimum water activity) of OTA produced by Aspergillus ochraceus (Aspergillus ochraus), Penicillium arcuate and Penicillium veratum were 0.83～0.87, 0.87～0.9 and 0.83～0.86, respectively; The optimum production temperature is 12～37℃, 4～31℃ and 4～31℃ respectively. Therefore, OTA-producing bacteria in the hot and humid south are generally dominated by ochra, which invades food and feed with moisture greater than 16%; while in the cold and dry north, it is dominated by penicillium, and some penicillium can still grow at around 0°C. , Which brings great difficulties to feed storage. In addition, the suitable toxin-producing substrates of different strains are also different. Madhyastha et al. (1990) reported that the toxin production of Aspergillus ochrae in peanut cake and soybean cake was significantly higher than that in wheat and corn. Penicillium is the opposite.

Under normal conditions, wheat and corn are less likely to be contaminated by OTA, about 1% to 5%, and their content is 0.01-5 mg/kg; barley and oats are more likely to be contaminated, about 10%, and their content is generally within Below 0.1mg/kg, individual samples are as high as 27mg/kg; according to Zust et al. (1989) and Egmond (1994), about 5%-10% of compound feed is contaminated, and OTA content is 0.05-0.4mg/kg.

Source

It has been found that 7 kinds of Aspergillus and 6 kinds of Penicillium can produce ochratoxin A, but they are mainly produced by Penicillium pure green, Aspergillus ochraceus and Aspergillus carnosus. The toxin mainly contaminates grains and agricultural products such as oats, barley, wheat, corn, animal feed and animal food (such as pig kidney, liver) and so on. Ochratoxin A is a derivative of phenylalanine combined with isocoumarin.

Physical and chemical properties

OTA was first purified by VanderMerwe et al. (1965) from the culture of Aspergillus ochraccus (Marquardt and Frohlich, 1992, reported that the bacterium is now called A. alutaceus). Wei Runyun et al. (1981) and Sun Huilan et al. (1989) also proposed pure OTA products from grain and compound feed respectively. Analysis shows that OTA is composed of 7-carboxy-5-chloro-8-hydroxy-3,4-dihydro-R-methylisocoumarin (abbreviated as Oa) and L-β-phenylalanine connected by peptide bonds. Into (see the chemical structure of ochratoxin A), molecular formula: C20H18CINO6, molecular weight 403.

OTB is a dechlorinated derivative of OTA, and OTC is an ethyl ester of OTA. OTA is a colorless crystal, soluble in organic solvents (chloroform and methanol) and dilute sodium bicarbonate solution, slightly soluble in water. OTA and OTB show green and blue fluorescence under ultraviolet irradiation, and the maximum absorption peaks are 333nm and 318nm, respectively.

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