Fried food flavor

Melton, S. L., Jafar, S., Sykes, D., and Trigiano, M. K. (1994). Review of stability measurements for frying oils and fried food flavor. ]. Am. Oils Chem. Soc. 71, 1301-1308. 

Heterocyclic compounds are primarily formed through non-enzymatic browning reactions. Recent studies of deep-fat fried food flavors led to the identification of pyrazines, pyridines, thiazole, oxazoles and cyclic polysulfides which had long-chain alkyl substitutions on the heterocyclic ring. The involvement of lipid or lipid decomposition products in the formation of these compounds could account for the long-chain alkyl substitutions. Model systems were used to study the participation of lipids in the formation of pyrazines, pyridines, thiophenes and cyclic polysulfides. 

In the frying process, food, such as vegetables, meat, or seafood, is brought in direct contact with hot oil. The food surface becomes golden yellow to dark brown in color and develops a pleasant fried food flavor. 

Fried food flavor develops as the frying process continues... 

Palm oil is the second largest source of oil in the world, next to soybean oil (55). Worldwide production of palm oil is increasing at a rapid rate and the volume of palm oil in the world may surpass that of soybean oil in the near future. Palm oil and palm olein (the liquid fraction) show excellent frying performance. In addition, both palm oil and palm olein produce a highly desirable fried food flavor (56, 57). 

Frying of food is an old and traditional means to prepare food quickly and enjoy the preparation for culinary delight. Fried foods are tasty because of the fried food flavor and the pleasant mouth feel produced by the oil absorbed in the fried food. This increases the salivation process that helps release of oil the soluble flavors from the fried food, making it very appealing to the taster. Fried food is popular in North and South America, Mexico, Europe, India, China, Japan, Malaysia, and elsewhere. 

Additional minor volatile compounds are found in both frying oils and in fried foods, including cis,trans- and trans,trans-2,4-decaderived from oxidized linoleate and 2,4-heptadienal derived from linolenate. The isomers of 2,4-decadienal impart a desirable fried food flavor in fried potatoes when present in small amounts, but excessive amounts of this aldehyde would be expected to cause undesirable rancid flavors. Furfural compounds may be derived from interactions between food sugars and proteins. Minor amounts of sulfur compounds and nitrogen-containing heterocyclic compounds (methyl pyrazine and 2,5-dimethylpyrazine in potatoes) may originate from Maillard reactions (Chapter 11). 

Review of stability measurements for frying oils and frying food flavor, J. Am. Oil Chem. Soc., 71 1301-1308. 

A good compilation of the functions of fats in various food products is available (26). Some functions are quite subtle, eg, fats lend sheen, color, color development, and crystallinity. One of the principal roles is that of texture modification which includes viscosity, tenderness (shortening), control of ice crystals, elasticity, and flakiness, as in puff pastry. Fats also contribute to moisture retention, flavor in cultured dairy products, and heat transfer in deep fried foods. For the new technology of microwave cooking, fats assist in the distribution of the heating patterns of microwave cooking. 

This complex unit operation involves significant microstructural changes in fact, most of the desirable characteristics of fried foods are derived from the formation of a composite structure a dry, porous, crispy and oily outer layer or crust, and a moist cooked interior or core, whose microstructures form during the process (Bouchon et al., 2001). The high temperatures (around 160 and 180°C) cause water evaporation, which is transferred from the food towards the surrounding oil, whereas oil is absorbed by the food replacing part of the released water. This process results in products with a unique flavor-texture combination (Mellema, 2003). 

Alkylpyrazines have been recognized as important trace flavor components of a large number of cooked, roasted, toasted and deep-fat fried foods (3). As a rule, alkylpyrazines have a roasted nut-like odor and flavor. Formation pathways for alkylpyrazines have been proposed by numerous researchers (4, 5, 6). Model studies suggest that they are minor products of the Maillard reaction. 

Interest in the influence of lipids on pyrazine formation has recently been generated by the identification of long-chain alkyl-substituted heterocyclic compounds in foods and in model systems. Pyrazines in this category include 2-heptylpyrazine isolated from french fried potato flavor (7), and 2-methyl-3(or 6)-pentylpyrazine and 2,5-dimethyl-3-pentylpyrazine, isolated from extruded zein/corn amylopectin/corn oil systems (8, 9). Only the involvement of lipids or lipid-decomposition products in the formation of these compounds could account for the long-chain alkyl substitution on the pyrazine ring. 

This paper discusses the formation and aroma characteristics of selected classes of heterocyclic compounds important to the flavor of foods, especially deep-fat fried foods. 

Pentyl-A-methyl-5-ethyloxazole was identified in french-fried potato flavor and has a strong buttery, sweet and lactone-like flavor. It is probably an Important contributor to the fried food aspect of french-fried potato flavor (37). 

With the emphasis in some parts of the world on a reduction in the dietary consumption of animal fats, the possibility of using blends of animal and vegetable fat has been explored. It has been shown that such blends confer some beef-like flavor notes on fried foods, and that foods fried in straight vegetable oils lack the characteristic flavors imparted by beef tallow. It is presently unclear whether the use of such animal-vegetable fat blends in frying will be widely adopted. 

Hexanal and 2,4-decadienal are the primary oxidation products of linoleate. The autoxidation of linoleate generates 9- and 13-hydroperoxides of linoleate. Cleavage of 13-hydroperoxide will lead to hexanal and breakdown of 9-hydroperoxide will lead to 2,4-decadienal (9). Subsequent moisture-mediated retro-aldol reaction of 2,4-decadienal will produce 2-octenal, hexanal, and acetaldehyde (10). 2,4-Deca-dienal is known to be one of the most important flavor contributors to deep-fat fried foods (11). 

Refining of crude rice oil involves dewaxing, degumming, neutralization of free fatty acids, bleaching to improve color, and steam deodorization. Refined rice bran oil is a light yellow color (Lovibond 3.0 R 30Y) with a mild background odor and flavor reminiscent of rice. Similar to peanut oil, the flavor and odor are complementary to the flavor of many fried foods, such as fish, chicken, and chips. 

Commonly, the fatty acids in food lipids are exposed to heat during oil processing and food manufacture. Once peroxides are formed, they can decompose and generate free radicals, and the rate of peroxide decomposition increases with temperature. Such reactions are of extreme importance to both consumers and processors, because of their flavor significance, and under frying conditions they can affect the physical, nutritional, and toxological properties of the fried food. 

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