MECHANISMS OF FORMATION IN FOODS AND BEVERAGES in .NET

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MECHANISMS OF FORMATION IN FOODS AND BEVERAGES
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was thermally desorbed from the ber and directly introduced into the GC injector and then detected by an electron capture detector (ECD). Using this method, 0.114 mg/L vodka (40% ethanol) of acrolein was determined (52, 53). A similar derivatizing agent, 2,3,4,5,6-penta uorophenylhyrazine (PFPH), was also used successfully to analyze trace amounts of acrolein (G). Acrolein PFPH adduct was analyzed using a gas chromatograph equipped with ECD or gas chromatography/mass spectrometry (GC/MS) (54). In this study, the detection limits of PFPH acrolein adduct by ECD and mass spectrometry/singleion monitoring (MS/SIM) were 16.60 fmol/mL and 1.31 pm/mL, respectively. Later, the same researchers determined acrolein formed from 2 g of sun ower oil heated at 220 C for 0 120 min using solid-phase microextraction with on ber derivatization (55). PFPH was absorbed onto a poly(dimethylsiloxane)/ divinylbenzene-coated ber and exposed to headspace of the heated sun ower oil. The derivative formed on the ber was subsequently desorbed into the GC with ECD for analysis of acrolein as PFPH adduct. The amounts of acrolein recovered by this method were 7.3 23.6 pmol. Since the recent developments in the sensitivity of GC/MS and headspace trapping devices, the use of a headspace/solid-phase microextraction/gas chromatography/mass spectrometry (HS/SPME/GC/MS) method without derivatization became common for acrolein analysis. Using this HS/SPME/ GC/MS method, direct analysis of acrolein has been conducted in various foods and beverages such as ewes milk cheeses (56), virgin olive oils (57), and sun ower oil (58). Furthermore, trace amounts of acrylamide, for which acrolein was hypothesized as one of the precursors (59), formed in asparagine/Dglucose Maillard reaction model systems were also successfully determined using the HS/SPME/GC/MS method (60). Acrolein is one of the precursors of genotoxic acrylamide, which is also formed in heat-processed foods.
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2.2.4 MECHANISMS OF FORMATION IN FOODS AND BEVERAGES As previously mentioned, the presence of acrolein in foods and beverages has been known for many years. However, acrolein had received much more attention as one of the hazardous air contaminants in urban and suburban areas than as a food component (61). Acrolein has been known to be released from certain manufacturing plants, such as acrylic acid and cornstarch manufacturing (62, 63), as well as in exhaust gases from both gasoline engines and diesel engines in signi cantly large amounts (64). However, acrolein was rst recognized as one of the volatile avor chemicals formed in foods. The formation of acrolein was observed in the degradation of amino acids, including methionine, homoserine, homocysteine, and cystathionine by heating at 100 C and neutral pH (12). It was hypothesized that methional was formed from methionine via Strecker degradation. Subsequently it was determined that methional formed acrolein by further oxidation. This step from methional to acrolein formation was accelerated signi cantly by the addition of air, or air plus ascor-
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bic acid or hydrogen peroxide (Fig. 2.2.2). This report suggests that amino acids are one of the sources of acrolein in foods. Major sources of acrolein in foods are heated lipids, which consist mainly of triglycerides of various fatty acids (65). Acrolein was proposed to form from the dehydration of glycerol when animal or vegetable fats were heated to high temperatures (2). As listed in Table 2.2.1, the major sources of acrolein are dietary oils such as corn oil, peanut oil, olive oil, and sun ower oil. Also, formation of various volatile chemicals, including acrolein, from lipids upon oxidation has been known (66). Hypothesized formation mechanisms of acrolein from triglycerides upon heat treatment are shown in Fig. 2.2.3. As shown in Fig. 2.2.3, the major source of acrolein has been known for many years as the dehydration of glycerol (67). Acrolein is also formed from formaldehyde and acetaldehyde, which are nal products of oxidative degradation of lipids, via aldol condensation and croton condensation although this is a minor pathway (68). Acrolein may also be formed from oxidative degradation of various fatty acids formed from triglycerides (66). The formation of acrolein through free radical mechanisms involving homolytic ssion of R O bonds more likely occurs at hightemperature treatment in food processing (25, 27) as well as through glycerol dehydration. The proposed radical mechanisms to yield acrolein from triglyceride are shown in Fig. 2.2.4. Recently, acrolein has begun to receive a great deal of attention as one of the minor precursors of acrylamide formed during food processing (69 71). For example, when acrolein and ammonia were heated at 180 C in the vapor phase, 753 mg/g ammonia of acrylamide was formed (59). A proposed formation pathway of acrylamide from acrolein is shown in Fig. 2.2.5. In this pathway,
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