# Methods for Determining Polycyclic Aromatic Hydrocarbons (PAHs) in Milk: A Review
## 2 Polycyclic Aromatic Hydrocarbons
### Sources of PAHs in Food and Dairy Products  
The lipophilicity of PAHs results in their accumulation in fat-rich food products. Milk and dairy products can be included in this group. Due to their high nutritional value, they are consumed by children and people in later adulthood worldwide as a dietary staple. Nutrition experts recommend the consumption of dairy products every day to anyone who can tolerate them [37,51]. The presence of PAHs in milk and dairy products primarily stems from the environmental contamination of feed, water, and grass, as well as the high-temperature processing methods applied to milk [37,40] (Figure 1).  
PAHs in food products originate either from the environmental contamination of raw materials (e.g., soils) or from their formation during high-temperature processing steps [52]. The exact pathway, at the level of technological processes, of their formation is not yet known. The three main mechanisms with the most significant impact on the formation of PAHs can be distinguished depending on the heat treatment used. However, they explain only part of the reason for the formation of PAHs in food. In the literature, one can see that this is an \"extremely complicated\" process [53]. PAHs are initially formed during pyrolysis and the incomplete combustion of organic matter. Key food components such as glucose, amino acids, and fatty acids degrade and cyclize during heating. The diversity and quantity of PAHs formed in food and food products during processing depends on several variables, including distance from the heat source, the fuel composition used, processing conditions, cooking time, and techniques such as reuse, conching, concentration, grinding, and storage. The three main pathways include the following:  
1. The pyrolysis of food components (proteins, fats, and carbohydrates) occurs at temperatures above 200 \({}^{\circ}\)C, with PAH synthesis intensifying between 500 \({}^{\circ}\)C and 900 \({}^{\circ}\)C. The pyrolysis of fats is the most significant contributor to PAH production.  
2. The dripping of lipids onto heat sources during thermal processing generates more volatile PAHs, which settle on the surface of food as smoke rises.
3. The incomplete combustion of charcoal, particularly in specific cooking methods, also produces PAHs that adhere to food surfaces [54].  
At the level of a chemical reaction, despite the uncertainty of researchers, several processes have been distinguished and described. They include, among others: hydrogen abstraction with acetylene addition (HA-M), condensation of PAHs with HAM, radical-induced PAH formation, Diels-Alder reactions, and phenyl addition with cyclization (ACP) [31; 55; 56].  
The most common food products are pyrene, fluorene, naphthalene, phenanthrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[e]fluoranthene, anthracene, fluoranthene, benzo[a]anthracene, chrysene, dibenzo[a,h]anthracene, benzo[ghi]perylene, indeno [1,2,3-c,d]pyrene, and benzo[a]pyrene [57]. The European Food Safety Authority's (EFSA) Scientific Panel on Contaminants in the Food Chain states that using only BaP to assess PAHs in products is insufficient. They recommend assessing PAH contamination in food using four key hydrocarbons (PAH4: benzo[a]pyrene--BaP, benzo[a]anthracene--BaA, benzo[b]fluoranthene--BbF, and chrysene--Chr) or an expanded set of eight (PAH8: PAH4 plus benzo[k]fluoranthene--BkF, benzo[g,h,i]pyrene--BghiP, dibenzo[a,h]anthracene--Dha, and indeno [1,2,3-c,d]pyrene--lcp). EU regulations specifically address PAH levels in food, tasking researchers, food safety professionals, and regulatory bodies with enforcing these limits to ensure safety [42; 58].