2.1.2. Ozonation

Ozone (O3) is a greenhouse gas made of three oxygen atoms. It is present naturally in the atmosphere (friend O3) or generated by human beings (foe O3) [26]. It can be produced by several methods, including UV-irradiation, electrical discharge of oxygen, and electrolysis of water. It is a highly reactive molecule having a high oxidizing effect (redox potential = 2.07 V), and it is used to mitigate many types of contaminants in food [62].

Ozone is used to reduce mycotoxins in food and feed, and it showed sanitation and antimicrobial effectiveness against viruses, bacteria, spores, and fungi [44]. The application of ozone to reduce or eliminate mycotoxins in foods and feeds can be performed by fumigation or in solution; the latter method is faster, as confirmed by a study where ozone solution at a concentration of 10 mg·L−<sup>1</sup> was used to treat a 1 <sup>μ</sup>g mL−<sup>1</sup> of deoxynivalenol (DON) solution for 30 s achieving a degradation rate of 54.2%. Meanwhile, the degradation rate was higher in scabbed wheat (moisture content = 17%) reaching 57.3%, when treated for 12 h with ozone gas (Concentration = 60 mg L−1). The high degradation rate of DON

can be established by increasing the concentration of ozone in solution and gas and by prolonging the application time [47].

Ozone fumigation of sun-dried herbs and spices showed that the main factors for achieving high microbial reduction and high aflatoxin degradation are the concentration of ozone and the exposure times. Ozone fumigation at 3 ppm for 210 min showed a considerable decrease in the total aflatoxins concentration by 93.75% in licorice and by 90% in peppermint. The disadvantage of this method is the reduction of the essential oil of chamomile by 57.14% and peppermint by 26.67% [44].

The degradation of trichothecene mycotoxins by aqueous ozone showed a pH sensitivity with maximum effectiveness at acidic pH of 4–6 and no effectiveness at alkaline pH of 9 [46].

Ozone treatment can be implemented during the storage of crops in a silo. In a previous study aiming at the decontamination of filamentous fungi, it was difficult to achieve homogeneity of ozone concentration in the silo during rice treatment following the application of 0.393 kg O3 m−<sup>3</sup> rice. The highest concentration of ozone was in the lower part of the silo, at the proximity of the ozone's inlet, suggesting a strong reduction of fungi in this area, while the effect of ozone gradually decreased while moving toward the upper parts of the silo [49].

Ozone is naturally unstable, leaving no residues in foods and feeds after its transformation into oxygen in the treated samples. It has a GRAS status (generally recognized as safe). It causes no waste and does not impose pollution problems [44,47]. At the industrial scale, the cost of ozone must be considered in developing countries [63].

Ozone gas applied to the rice silo did not damage the rice quality. No significant changes were perceived, especially in starch modifications, lipid peroxidation, protein profile, and microstructure alteration [49]. Concurrently, the treatment of parboiled rice during the maceration stage showed many advantages in the quality of the treated rice, such as higher head rice yield, higher luminosity and hardness, decreased cooking time, percentage of defective grains, and the abundance of soluble protein [45].

As shown in Table 1, the ozonation appears to be more effective in reducing the microbial load than in reducing mycotoxins already produced in food or feed. Higher aflatoxin reduction rates are achieved in powdered herbs and spices than in intact grains, wheat, and rice. The organoleptic and nutritional characteristics are affected differently in diverse food matrices. They range from no significant modification, or a slight improvement in quality attributes of wheat and rice, to a detrimental effect on the essential oil of herbs and spices [44,47–49].
