Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 1 Physical and chemical reactions that occur during frying.
in understanding how food fries, and how heated oils and their degradation products
interact with fried foods. This knowledge will also help in optimizing the frying
process by controlling the process to produce good-quality food and oil with longer
fry life. Blumenthal [3] not only described the physical mechanisms that take place
as a french-fried potato is fried, but also outlined procedures to optimize the frying
process in order to increase frying oil life and decrease oil absorption into food.
Blumenthal also proposed conducting basic frying studies using model foods that
have surface-to-volume ratios characteristic of some fried food, including cotton balls
(all interior volume, crispy exterior surface to represent battered and breaded
chicken); french fried potatoes (significant interior volume, significant external surface),
and potato chips (large surface area, little interior volume). Alexander et al.
[4] compared corn, peanut oil, and partially hydrogenated soybean oils heated in
open containers with those heated in a pressurized deep-fat frying system and reported
that pressurized deep frying with fats resulted in less deterioration than openvat
heating, as shown by chemical analyses. In discussing physical changes in food
during frying, Pokorny [5] reported that oil is absorbed into the fried material and
adsorbed on its surface and that oil losses depend on the type of fried food; for
example, potatoes absorb more oil than meat. Sun, Moreira, and Palau [2,6,7] have
extensively studied the fundamental mechanisms of deep-fat frying using tortilla
chips as model food and have suggested approaches to reducing chip fat content
from a food engineering approach.
Physical and chemical changes in oils that occur during heating and frying are
presented in Table 1. Although there are specific methodologies for quantitative measurement
of degradation processes and products, some qualitative changes can also
be determined subjectively by visual inspection. Although these practices are not
recommended, many small-scale oil users, such as restaurants, discard frying oils
when frying causes excessive foaming of oil, or when the oil tends to smoke exces-
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