Triglycerides irradiation

Table I summarizes the various meats, meat constituents, and other related substances which have been analyzed, including substances reported on previously (6) as well as those for which new data are given. The substances chosen are intended to provide a cross-section of the type of inherently related material from which volatile irradiation odor and flavor compounds might be expected to form. Thus, in addition to several whole meats, the volatile irradiation products from a number of protein and lipid substances have been analyzed. Among the lipid substances included are typical whole fats and separate moieties such as triglycerides, fatty acid esters, and cholesterol, as an example of a steroid. Among the proteinaceous substances included are a protein, a polypeptide, and some individual amino acids. Finally, beef itself has been separated into a protein, a lipid, and a lipoprotein fraction, and these have been separated, irradiated, and analyzed.

It is now well established (6,10) that the hydrocarbons, except possibly those having three or four carbon atoms, found in the irradiated meats can come only from the lipid. This hypothesis has been verified in earlier studies, when the volatiles from irradiated methyl oleate (10) were found to contain appreciable quantities of alkanes and alkenes, and now in more detail from studies of both triglycerides and fatty acid esters. 

Most of the other products found in irradiated meat volatiles except those containing sulfur or aromatic rings may also be accounted for by mechanisms associated with alkyl free radical formation in the fat. Oxygenated compounds are far less abundant than hydrocarbons, but appreciable amounts of a homologous series of n-aliphatic alcohols up to hexanol are found. Of these, only ethanol is detected in the unirradiated controls. Since the water content of meat averages nearly 60%, the formation of alcohols may be thought to occur by reaction of the alkyl free radical with water. Such a mechanism is supported by the fact that only traces of alcohols are found in irradiated dry butterfat and were undetected in irradiated triglycerides or methyl esters of fatty acids. 

The generality of the sequential formation and reaction of free radicals, initiated by either electrons or hydrogen atoms, is borne out by ESR spectral data on irradiated fats from beef, pork, and chicken [14]. Each fat contains a diverse combination of triglycerides with differing proportions of fatty acid moieties. Figure 8 shows the spectra for beef fat [1]. Though the same most stable radical is ultimately formed in all cases, Sevilla [29] has shown in low dose studies that this radical disappears more rapidly in chicken fat than in pork fat (Figure 9). The former has more of the unsaturated linoleic acid than the latter and presumably has a lower viscosity. All of these results imply a commonality in the radiolysis of the lipids. 

The overall yield of radiolysis products is relatively low and their distribution will depend on the fatty acid composition of the triglycerides. In meats irradiated in the absence of oxygen, low levels of the free fatty acid, the associated propanedioldiester, hydrogen, and products derived from the triglyceride radical are to be expected. Much lower yields of volatile hydrocarbons are produced that provide insight into other scission processes and reaction pathways [27, 30, 31],... 

That the radiolysis of meats containing similar proteins and comparable fatty acids involves similar primary and secondary processes leading to a common set of radicals stable at -40°C is shown by the ESR spectra in Figure 12 for irradiated, enzyme-inactivated chicken, beef, ham, and pork [3, 62], These spectra reflect the commonality in radicals derived from the muscle proteins, myosin and actin, and fi-om the constituent triglycerides, which have slightly different fatty acid compositions. The minor consequences of this compositional... 

Figure 18 Relationship of the dose noimalized yield of propanedioldipalmitate to its triglyceride precursors in four muscle foods irradiated to 10, 60, and 90 kGy at -40°C. Adapted from Merritt et al. [17] with permission.

Sample preparation. To determine cyclobutanones in irradiated food it is necessary to isolate the lipids. This can be performed as described for hydrocarbons (Section 7.3.1). Because of the polar character of cyclobuta-none the separation of cyclobutanones from triglycerides is more difficult. Cold-finger distillation can be used but chromatographic techniques seem to be more suitable. Column chromatography using florisil has been applied successfully in order to solve the problem. Therefore the sorbent has to be deactivated carefully with about 5% water. This method can be optimized by the operator. The chemicals must be tested to exclude contamination with interfering substances. Since cyclobutanones do not appear naturally they cannot contaminate the reagents. 

As described above, 2-alkylcyclobutanones are the only cyclic irradiation products produced under food irradiation conditions. Le Tellier and Nawar (1972a) reported the formation of 2-alkylcyclobutanones. It was shown that a series of homologous 2-alkylcyclobutanone is formed in simple triglycerides (fatty acids with 6-18 carbon atoms). The number of carbon atoms is identical to the number of carbon atoms in the precursor acid. In 1991 Boyd and Stevenson published a method for the determination of 2-dodecylcyclo-butanone. It should be re-emphasized that 2-alkylcyclobutanones have never been detected in non-irradiated samples. Two general conclusions can be drawn from these results irradiated foods can be detected, and these marker substances are the first that have not been detected in thermally treated foodstuffs. 

Thionation of Carboxylate Esters and Lactones. The reaction of esters and lactones with LR represents a well-established method for the synthesis of the corresponding thiocarbony 1 deriva-tives. - In fact, LR is the much superior reagent for the thionation of esters as compared with phosphorus pentasullide. Open-chain thionoesters have been conveniently obtained. Interestingly, natural triglycerides also smoothly react with LR to yield pure tristhionotriglycerides. Even better results are obtained with carboxylate esters if the improved solubilized LR or microwave irradiation are applied. The method has particularly been used for the preparation of cyclic thionoesters. Obviously there are very few structural or other restrictions that inhibit the formation of y-,S-, or macrocyclic thionolactones. Once more, microwave irradiation significantly improves the re-... 

For this purpose, for the preparation of rapeseed and linseed oil-based polyols a two-step process was applied.In the first step, the double bonds of the unsaturated triglycerides were transformed into oxirane rings with acetate peroxyacid to form epoxidized oil. In the second step, the ring opening reactions of the epoxy groups with monoethylene glycol (MEG) or DEG afforded the oil-based polyols. For rapeseed and linseed oils, it was reported that microwave irradiation can be applied for both steps of the process. In comparison to the processes under conventional conditions, reduction of the reaction time of epoxidation reaction (ca. 60%) and, then, the hydroxylation step (ca. 75%) was observed. 

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