## 1 Introduction
Therefore, the process parameters should be optimized to the microbiological profile and the type of raw material. Particularly spore-forming Gram-positive bacteria and yeasts are more vulnerable than Gram-negative bacteria and molds [2; 23; 24]. Moreover, ozone is a highlyoxidizing agent, which could possibly cause the decomposition of essential oils when used for long periods or in high concentrations. This is especially important in the case of spice plants used to improve aroma and taste [25]. In Europe, the use of gaseous ozone is controversial. The European Food Safety Authority (EFSA) is still validating the use of ozone for fresh food. The EFSA publication \"Scientific opinions on the risks posed by pathogens in food of non-animal origin (_Salmonella_ and Norovirus in leafy greens eaten raw as salads and berries)\" suggests using ozone, as well as other sanitizing molecules, for decontamination of leaf vegetables and berries [26]. Another more recent EFSA document, \"Outcome of the consultation with Member States and EFSA on the basic substance application for approval of ozone to be used in plant protection as a bactericide, fungicide, insecticide, nematicide, and vircide\", states that ozone should not be approved as a basic substance, due to its hazardous properties. However, ozonated water could be considered eligible for approval as a basic substance. Therefore, the assessment should be focused on ozonated water instead of gaseous ozone [27]. Parsley (_Petroselinum crispum_) is famous for its high content of bioactive compounds, such as phenols, flavonoids, vitamin C, chlorophylls, carotenoids, and minerals [28; 29; 30; 31; 32; 33]. Parsley also shows significant antioxidant, antibacterial, and antifungal activities [34; 35; 33]. Parsley leaves were used by the ancient Greeks and Romans as a herb. Nowadays, parsley is cultivated all over the world and is widely used as a flavoring and aromatic food additive. Therefore, it is an interesting research object. Parsley leaves are used fresh or dried, and their slightly aromatic flavor is popular with fish, meats, soups, sauces, and salads [36]. In addition, parsley has a long history in traditional and herbal medicine. The plant has been used to alleviate menstrual pain and has anti-inflammatory properties [35]. However, the use of fresh parsley leaves may be associated with a significant increase in microbial risk as well as a decrease in shelf life due to the high number of microorganisms. Parsley is usually planted and grown under controlled conditions but is often irrigated using various organic fertilizers or contaminated water [37]. Therefore, similar to other leafy greens considered to promote healthier living, parsley has been frequently linked to outbreaks of foodborne diseases [38]. Parsley leaves may become contaminated by a wide range of microbes, which can cause spoilage and pose a public health risk [30; 39; 40]. The most common pathogens contaminating plant material are _Salmonella_ spp., _Bacillus cereus_, _Staphylococcus aureus_, _Clostridium perfingens_, and _Escherichia coli_[2; 3; 41]. Contamination can occur both pre- and post-harvest (during cultivation, harvest, drying, transport, and storage) [3]. Sources of microorganisms include soil, water, dust, dirt, insects, fecal materials from animals, and even human excrement [41]. As a result, the microbiological compositions of herbs and spices vary depending on the climate, weather, and season. The aim of this study was to evaluate the effectiveness of ozone water treatment on microbial decontamination of parsley leaves. There are few studies investigating the effects of different decontamination processes of fresh parsley leaves [42; 43; 44]. The effectiveness of ozonation was examined by microbiological and physico-chemical assays, with special attention to the color of the plant material.