Food Lipids: Chemistry, Nutrition, and Biotechnology

long periods of heating developed lower TBA numbers than did samples subjected
to lower temperatures for shorter periods of time. Differences previously found in
method of cooking [317,318] therefore reflected differences in quantity of heat applied.
In other cases, differences found to be characteristic of various cooking methods
reflected variability in water loss rather than differences in the extent of oxidation.
When TBA numbers were expressed per gram tissue, Pikul et al. [319]
calculated that microwave cooking led to lower numbers than convection oven cooking.
When expressed per gram of fat, however, the differences in results between
microwave and convection cooking were not significant.
Length of refrigeration prior to cooking also affects the response of muscle
tissue to cooking. Erickson [320] found that cooking of minced fish stored for 5
days generated greater amounts of either TBARS or fluorescent pigments than cooking
of product stored for 7 days. A decreased loss of �-tocopherol in cooked 7-day
product compared with cooked 2- or 5-day product gave further support to the conclusion
that lipid oxidation had been inhibited during cooking in the 7-day sample.
Change in pH, polyamines, Maillard reaction products, microbial removal of hydroperoxides
and secondary oxidative products [367], and/or phospholipase activity
were postulated as potential factors involved in the decreased response of refrigerated
product to cooking.
I. Deep Fat Frying
A specialized form of cooking is deep fat frying, in which the product is immersed
in hot cooking oil for some period of time to totally or partially cook it. Not only
does the oil serve as the medium for heat transfer, it reacts with the protein and
carbohydrate components of the food, developing unique flavors and odors that have
definite appeal to the consumer. For breaded products, deep fat frying also sets the
batter, which binds the breading to the product surface.
A number of variables in addition to time and temperature of frying may impact
the susceptibility to oxidation of a fried muscle product. Oil quantity is one of these
variables. During frying, the product loses moisture and absorbs oil. When this absorbed
oil is oxidized to any extent, it accelerates degradation of the product. Breading
is another variable affecting oxidative susceptibility through attenuation of the
response to oil quality. Breading inhibits the loss of moisture and absorption of frying
oil [368], with finely ground breading material decreasing oil absorption to a greater
extent than coarsely ground material [369]. Since batter and breading are in intimate
contact with surface lipids, the catalysts, activators, and inhibitors present in the
batter and breading also have the potential to affect lipid oxidation of the fried
product.
J. High Pressure
Increasing attention has been directed in recent years to the application of high
hydrostatic pressures (up to 800 Mpa) to inactivate microorganisms [370]. Another
distinct advantage claimed for pressurization is that heat-labile compounds undergo
limited degradation compared with heat processing [371]. While high hydrostatic
pressure treatment on cod and mackerel muscle prevented hydrolysis of phospholipids,
a slight acceleration in lipid oxidation was noted under these conditions [321].
Similarly, oxidation of sardine lipids was accelerated by a high pressure treatment,
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