Frying process during

How proline is converted to NPYR has not yet been fully elucidated and could conceivably occur by either of two pathways (29, ). One pathway involves the initial N-nitrosation of proline, followed by decarboxylation, while in the other, proline is first decarboxylated to pyrrolidine followed by N-nitrosation to NPYR. Since the conversion of N-nitrosoproline (NPRO) to NPYR occurs at a much lower temperature than the transformation of proline to pyrrolidine, the pathway involving intermediacy of NPRO is thus the more likely route ( ). It has been reported that preformed NPRO in raw bacon is not the primary precursor of NPYR in cooked bacon (29,33-5), as shown by the fact that ascorbyl paImitate, when added to bacon, inhibits the formation of NPYR (33). However, this by no means rules out the intermediacy of NPRO which could be formed at the higher temperatures attained during the frying process (29,36). 

The mechanism of NPYR formation has been studied by Coleman (37) and Bharucha et al. ( ). Coleman (37) reported that the requirement for a high temperature, the inhibitory effects of water and antioxidants, and the catalytic effect of a lipid hydroperoxide are consistent with the involvement of a free radical in the formation of NPYR. Similarly, Bharucha et al. (29) suggested that, since both NPYR and NDMA increase substantially towards the end of the frying process, N-nitros-amine formation during frying of bacon occurs essentially, if not entirely, in the fat phase after the bulk of the water is removed and therefore by a radical rather than an ionic mechanism. These authors speculated that, during the frying of... 

Torres, P., Guzman-Ortiz, M. and Ramirez-Wong, B., Revising the role of pH and thermal treatments in aflatoxin content reduction during the tortilla and deep frying processes, J. Agric. Food Chem., 49, 2825, 2001. 

Zaiifar, A. M., Achir, N., Courtois, F., Trezzani, I., and Trystram, G. (2008). Review of mechanisms, conditions, and factors involved in the oil uptake phenomenon during the deep-fat frying process. Int. J. Food Sci. Technol. 43,1410-1423. 

Amino acid analysis confirmed that Maillard browning reactions occurred during the frying process, since basic amino acids such as lysine and arginine decreased significantly, whereas all others decreased only slightly (Table I). 

Oil acts as a heat transfer medium during the frying process which rapidly heats, cooks, and sometimes puffs, dehydrates, or forms a crust around the product. The mechanics of deep fat frying are shown in Fig. 34.32.173 The entering material carries oxygen that temporarily aerates the hot oil, and water that forms steam, with both rapidly swept out... 

Fats and oils are heated during commercial processing and during frying. Heating during... 

The content of polymers and polar components in oils increases during frying process. Size exclusion chromatography and HPLC may be used for the analysis of such components. The content of polar lipids should not exceed about 20%. 

Free radicals are formed whenever oil containing unsaturated fatty acids is heated in the presence of a metal initiator, (25) such as iron, nickel, or copper. Free radicals are formed in the oil during frying. The metal initiator in the frying process can come from several sources as given below ... 

Some of these delicate flavor components are claimed to penetrate into the food during frying. This improves the flavor of the product compared with the conventional frying process. 

The volatiles in the frying oil increase in the beginning, but then decrease as frying continues. The most important volatiles for the quality of frying oil are saturated aldehydes Cg-Cg, enals (e.g., 2-decenal), dienals (e.g., 2,4-heptadienal), and hydrocarbons (hexene, hexane, heptane, octane, nonane, and decane). The presence of volatile oxidation products formed during the frying process was discussed by Perkins (1996) and Nawar (1998). 

Christie, W.W. and Dohson, G. 2000. Formation of cychc fatty acids during the frying process, Eur. J. Lipid Sci. TechnoL, 102, 515-520. 

During the frying process the lipid material is exposed to high temperature in the presence of air and moisture. Under these conditions a wide variety of reactions takes place and the main groups of alteration compounds generated are summarized in Table 59.5 [11,25,7,16]. 

Kawas, M.L. and Moreira, R.M. 2001. Characterization of product quality attributes of tortilla chips during the frying process, J. Food Eng., 47 97-107. 

Kalogeropoulos N, Chiou A, Mylona A, loaimou MS, Andrikopoulos NK (2007) Recovery and distribution of natural antioxidants (a-tocopherol, polyphenols and terpenic acids) after pan-frying of Mediterranean finfish in virgin olive oil. Food Chem 100 509-517 Cacace JE, Mazza G (2003) Mass transfer process during extraction of phenolic compounds from milled berries. J Food Eng 59 379-389... 

Oil always breaks down during frying. Restoration of oil after use is not beneficial. Oil must be treated from the very beginning so that breakdown components of the oil, which act as catalysts for further oil degradation, are removed continuously without accumulating in the oil. There are various methods for oil treatment. They add benefit as well as complexity and cost to the operation. A careful study of the frying process, as well as that of the oil treatment operation, is needed to make an intelligent choice. Finally, one must look into prevention for oil breakdown and then develop a plan that would be an optimum combination of preventive measures and oil treatment process. 

In the models described above, a constant convective heat transfer coefficient was assumed during the hole frying process, or two independent values were considered (1) one for the initial frying stage... 

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