Introduction

Mycotoxins are biological toxins produced by specific fungi and can be presented in agricultural products under warm and humid conditions as a result of mold contamination of crops, during both pre- and post-harvest. They may cause health hazards to humans and livestock, ranging from acute poisoning to long-term effects such as immune deficiency and cancer (Cavaliere et al. 2007; Ferracane et al. 2007). Almost 25% of the world’s harvested crops are spoiled by mycotoxins, this causes annual significant losses in agricultural and industrial sectors in billions of dollars (Agriopoulou et al. 2020). According to the International Agency for Research on Cancer (IARC Working Group on the Evaluation of Carcinogenic Risks to Humans 2012), mycotoxins are hazardous contaminants to human and animal health and as top ten hazards based on Rapid Alert System for Food and Feed. Among the several hundred mycotoxins identified until now, around a dozen have gained the most attention due to their severe effects on human health and their presence in food (IARC Working Group on the Evaluation of Carcinogenic Risks to Humans 2012; Agriopoulou et al. 2020). Based on the report of the IARC and WHO in 2016, 500 million people are exposed to natural toxins, such as mycotoxins, daily and 160 million children under the age of five are stunted in develo** countries (Agriopoulou et al. 2020). Public concern about possible presence of mycotoxins in food has increased in recent years due to the increasing awareness of the health impact.

Aflatoxins (AFs) are a group of greatly toxic mycotoxins produced by certain fungi of the genus Aspergillus, such as Aspergillus flavus and Aspergillus parasiticus (Markaki 2010). AFs are potent carcinogenic, teratogens, hepatocarcinogenic, nephrotoxic and mutagens mycotoxins (Ferracane et al. 2007; Markaki 2010). Proportion of AFs in mycotoxins were reported 82% in 2018 (Agriopoulou et al. 2020). Four main AFs (B1, B2, G1, and G2) of 20 occur naturally in contaminated plant products (Cavaliere et al. 2007). Aflatoxin B1 (AFB1) has classified in Group 1 as human carcinogen (IARC Working Group on the Evaluation of Carcinogenic Risks to Humans 2012; FAO/WHO 2015) which usually is the most concerning and poisonous among these toxins. Consequently, detection of AFB1 has become important in terms of safety, import and export of food products.

Vegetable oils are important part of the human diet; therefore, safety of these oils and their conformity assessment based on national and international standards are essential and necessary to maintain the consumer’s health and fair trade. Soybean, rapeseed, sunflower seed, peanut, sesame and olive oils are major oils which extensively used for cooking in the world (Bao et al. 2010; Zhao et al. 2017a). Vegetable oil is known as one of the main mycotoxin-contaminated foodstuffs (Bordin et al. 2014; Li et al. 2019). AFB1 is reported as one of the main harmful constituents and risk factors of edible oils (Liu et al. 2017). Existing reports reveal the contamination of majority of edible oil-yielding seeds by various fungi, resulting mycotoxins production (Bhat and Reddy 2017). Since most of the mycotoxins are fat soluble and not easily eliminated from the body, mostly accumulated in fatty tissues (Idris et al. 2010).

Different kinds of olive oils are popular worldwide, especially in Mediterranean countries they have notable increase in consumption rate (Özcan et al. 2019; Gumus et al. 2020; ** countries (Agriopoulou et al. 2020). Further, virgin olive oil and extra virgin olive oil may be contaminated by mycotoxin such as aflatoxin G1 (AFG1) with incidence rate of 18% (Hidalgo-Ruiz et al. 2019). The available data on olive oil contamination by OTA or other AFs such as AFG1 in the literature did not meet sample size requirement for meta-analysis.

Despite of high consumption of olive oil in Mediterranean country and increasing consumption rate in the world, studies regarding contamination of olives or olive oil with mycotoxin are limited compared to the other agricultural products (Ben Rejeb et al. 2009). Also, hazard assumed as insignificant, since OTA and AFB1, have been discovered in extra-virgin olive oil hardly or at very low concentration (Alamprese 2014). It should be noted that aflatoxin concentrations in food generally do not make an acute unfavorable effect on consumers, but continuous exposure may cause significant hazard to users (Agriopoulou et al. 2020). Recently, unrefined olive oils under the legal limit reported to have potential risk of liver cancer for adult and children (Nabizadeh et al. 2018). While olives and olive oil are a principal component in the Mediterranean diet, even low levels of contamination may cause danger to public health due to its high daily intake (Ben Rejeb et al. 2009).

Although there is considerable progress in development and validation methods of mycotoxins analysis in olive oil (Bao et al. 2010; Dridi et al. 2015; Zhao et al. 2017a, b; **ao et al. 2018; Hidalgo-Ruiz et al. 2019; Karunarathna et al. 2019; Zhang and Xu 2019; Yu et al. 2019), there is limited researches when it comes to the occurrence of AFs and OTA with categorical data based on factors affecting the incidence of mycotoxins in olive oils.

It assumed that refining process will remove or reduce mycotoxins in vegetable oils (Lacoste et al. 2005; Banu and Muthumary 2010; Idris et al. 2010; Mariod and Idris 2015; Nabizadeh et al. 2018; Karunarathna et al. 2019), depends on the oil type and refining method (Banu and Muthumary 2010). Although the opposite is also true, recently contradictory results in the literature with 73% of zearalenone contamination in refined olive oil were reported, despite the probability of mycotoxin elimination in refining process (Hidalgo-Ruiz et al. 2019). To declare the effect of refining on mycotoxin elimination further studies on refined and unrefined olive oil is required. It should be considered that nutritional characteristics belong to the virgin olive oils category consumed without refining process.

It seems that more researches are required to correlate mycotoxin contamination to chemical and sensorial characterization. Acidity as one of the main quality index of olive oil could be influenced by mold growth (Finoli et al. 2005). It has been mentioned that mycotoxins have no odor and do not change the organoleptic properties (Agriopoulou et al. 2020), However, presence of fungi in virgin olive oil could be detected as negative attribute by panelist as musty flavor due to fungi growth on stored olive in humid conditions for a couple of days (IOC 2018a). This may be correlated to the presence of mycotoxins in olive oils, although there is a research gap when it comes to identifying the actual stage of olive fruit or olive oil contamination by mycotoxins (Bhat and Reddy 2017).

To guarantee consumer safety against risk of contaminants, specific attention to the level of contaminations in foods is needed. Consequently, international and national organizations set maximum residual limits (MRLs) for different contaminations. To the best of our knowledge, there is no legal limit for mycotoxins in vegetable oil in international standards such as CODEX. Generally, in such standards it has been mentioned that “The products covered by this standard shall comply with the maximum levels of the general standard for contaminants and toxins in food and feed” (FAO/WHO 2015). In addition, International Olive Council (IOC) refers to MRLs established by the Codex standard for olive oil (IOC 2018b). The European Commission (EC) sets the maximum level (MRL) for different food products (2–12 μg/kg AFB1 and 4–15 μg/kg total aflatoxins), although edible oils as well as olive oils are not particularly addressed (The Commission of the European Communities 2010). In some countries there are national standards considering MRLs for AFB1 and total aflatoxins in food, such as United States and China (20 μg/kg) (**a et al. 2021). There are limited countries using MRL for AFB1 monitoring in vegetable oils, such as China (< 10 μg/kg) except for corn oil and peanut oil (< 20 μg/kg), Russia (< 5 μg/kg), Morocco (< 5 μg/kg) and Kenya for total aflatoxins of B1, B2, G1, G2 (< 20 μg/kg) (Romer Labs 2012).

Establishment of the maximum residue limits for mycotoxins is based on total diet study, occurrence of mycotoxins in different foods and calculation of intake of contamination through food consumption basket in each country. However, mycotoxins may occur in low amount in edible oils like olive oil, it may become an important risk source due to its high consumption in some countries such as Mediterranean countries; consequently, risk assessment study is recommended.

Conclusion

Prevalence of aflatoxins in olive oils has been reported worldwide. Since AFB1 is a carcinogenic and genotoxic substance, low levels of contamination can create a hazard to public health. This is of more significance since olives and olive oil are major constituents in the Mediterranean diet. As a measure of safety for human health, the need to regulate mycotoxins for edible oils is emphasized. Mycotoxin reduction and prevention management strategies before and after harvest are also essential to protect the consumers. In order to assess the risk of mycotoxins in diet, the cumulative amount of mycotoxin intake through the diet and various sources such as cereals, coffee, nuts, spices, etc. needs to be considered. Since the fact that olives and olive oil are the main parts of the Mediterranean diet, despite the low levels of aflatoxins and OTA found in some studies, overall concentrations of contamination are also required.

There are a few studies regarding occurrence and concentration of mycotoxins in olive oils based on categorical data and variables which affecting on the incidence of mycotoxins such as type of olive oils, refined or unrefined samples, country and origin of samples, organic agriculture versus traditional agriculture, packed or labeled versus unpacked olive oils. More primary studies are needed in this area based on detailed data of means, standard deviations, sample sizes, type of the olive oils from different countries and even different parts of a specific country as broad variance of daily consumption of olive oil in Mediterranean and non-Mediterranean countries. It should be pointed out that, there were some controversy or inconsistency in the results of primary researches and available reports which indicate the need for meta-analysis and subgroup analysis to reach conclusive results. Risk assessment of mycotoxins in olive oils and setting the maximum residual levels of mycotoxins in it, at least for countries with high consumption of olive oil, are also recommended.