## 3 Results and Discussion
### Considerations of General Health Risks Posed by Human Exposure to Aldehydic LOPs
#### 3.7.3. Carcinicities of Selected \(\alpha\),\(\beta\)-Unsaturated Aldehydes
Our previous \({}^{1}\)H NMR-based studies have also demonstrated that shallow frying practices give rise to much greater levels of LOPs than those observed during deep frying episodes performed under the same experimental conditions and temperature. This observation reflects the influence of the surface area of the frying medium, and hence its exposure to atmospheric O\({}_{2}\), and also the subsequent dilution of LOPs generated into the bulk frying medium [12]. However, in a toxicological context, the lower levels of aldehydes found in deep-fried culinary oils may, at least in part, be compromised by the greater extent of oil absorption or exchange by the fried food matrix under these frying conditions. Intriguingly, concentrations of aldehydes arising from the thermal stressing of commercially available, PUFA- or MUFA-rich culinary oils is a value representing only that _remaining_ therein [12; 13; 15; 19]. Certainly, a large number of the aldehydes generated are volatilised at standard frying temperatures, and this may also present serious health hazards in view of their inhalation by humans, especially those working in fast-food retail outlets or restaurants with insufficient or inadequate ventilation precautions, or those performing classical Chinese-style wok cooking episodes domestically. This is especially the case for aldehydes arising from the peroxidation of linoleicyl- and linolenoyglycerols (particularly deca-_trans_,_trans_-2,4-dienal and acrolein, respectively), since the great majority of aldehyde secondary LOPs generated therefrom have boiling-points (b.pts) <180 \({}^{\circ}\)C [49], at least some of them substantially so. In view of the above considerations, the'safety' criteria outlined by many researchers, e.g., those provided in [44] are therefore an unrealistic representation, i.e., one which furnishes an incomplete message to scientists, readers and consumers regarding the consumption of fried foods laden with the oils in which they have been heated according to either shallow- or deep-frying processes, and therefore also the proportionate, frying oil FA unsaturation status-dependent concentrations of LOPs contained therein. Notwithstanding, unless they have been exposed to such frying practices, or alternatively stored for prolonged periods of time at ambient temperature and/or exposed to light, we agree that PUFA-rich vegetable seed oils offer little or no threats to human health; indeed, they contain essential FAs such as linoleic and \(\alpha\)-linolenic acids. However, since some researchers focused on the positive health benefits offered by PUFA-rich CFOs appear not to have considered the thermally induced generation of LOPs during frying practices, such'safety' arguments on this point are moot, and poorly representative of'real-life' scenarios. As an example, Ref. [44] shows the lipid hydroperoxide (i.e., HPM plus CHPD) levels of these oils _before_ they have been exposed to either shallow- or deep-frying practices: if that is the concentration of these agents before exposure to such high temperature stresses, how much will be present thereafter, let alone those of cytotoxic and genotoxic aldehydes generated from their fragmentation? This is therefore a major scientific as well as public health concern. The authors of [44] correctly state that '... animal fat is also prone to degradation during cooking since it does not consist of saturated fat only, but is rather a combination of SFA, MUFA and PUFA, in different ratios'; however, they do not indicate that such fats contain much lower PUFA contents than those of commonly employed seed or other vegetable oils (only ca. 5% (\(w/w\)) for pork or beef tallows), and are therefore much less susceptible to oxidative damage during standard frying or cooking practices. These researchers, together with many others, also attempt to rationalize and emphasize the critical importance of omega-6 to omega-3 FA ratios in the oils tested as a 'health index' parameter, with 'desirable' values of 2.0-5.1 quoted [1].