Environmental Engineering Reference
In-Depth Information
taBle 20.1
Goals for redesigning soybean oil composition for
specific Food and Industrial applications
Percent crude soybean oil
desired composition for
specific use
Fatty acid
normal oil
Frying
Baking
Industrial
Saturated (16:0 + 18:0)
15
7
42
11
Oleic (18:1)
23
60
19
12
Linoleic (18:2)
53
31
37
55
Linolenic (18:3)
9
2
2
22
Source:
Wilson, RF.,
Soybeans: Improvement, Production and Uses
, 3rd ed,
American Society for Agronomy, Madison, WI, 621-677, 2004.
Soybean oil contains a high concentration of polyunsaturated linoleic (18:2) and linolenic (18:3)
acids. These fatty acids have a high number of double bonds, which are susceptible to oxidation,
resulting in reduced shelf life, low stability at high cooking temperatures, and off-flavors. Oxidation
of linolenic acid with three double bonds causes this fatty acid to contribute most to the poor
functionality of soybean oil. To improve oxidative stability and undesirable taste, soybean oil is
hydrogenated to reduce double bonds, which are sites of oxidative attack and subsequent off-flavor
development (Yadav 1996; Liu 1999). Partial hydrogenation of soybean oil increases oxidative sta-
bility but leads to the formation of
trans
-fats. Demand from oil seed processors for a lower-cost
alternative to catalytic hydrogenation for producing oil products with desired flavor and function-
ality led to research to breed soybeans containing lower linolenic acid (Liu 1999). More recently,
health concerns and labeling laws that require listing the amount of
trans
-fatty acids in foods have
prompted food companies to seek alternative oils to replace hydrogenated soybean oil to ensure that
their products contain low levels of
trans
-fats. Thus, emphasis on soybean oil with 3% linolenic acid
or less has become a high priority (Yadav 1996; Wilson 2004).
In most Asian countries, soybeans are usually consumed directly in products such as tofu, sprouts,
soybean paste, and health supplements. As essential fatty acids, linoleic and linolenic acids are desir-
able components of soybean oil. Linoleic acid (ω6) and linolenic acid (ω3) are potential precursors of
eicosapentaenoic acid (EPA; 20:5) and docosahexaenoic acid (DHA) (22:6), which can have multiple
positive health benefits in diets including reduction of cardiovascular disease and improved cognitive
function (Connor 2000; Brouwer et al. 2004; Gebauer et al. 2006). Studies suggested that adjusting
the intake ratio of ω6 to ω3 fatty acids may enhance overall health (Able et al. 2004). Thus, for health
benefits, elevated 18:3 genotypes are desirable in food-grade soybeans. Also, oils low in saturates and
high in polyunsaturated fatty acids and linoleic and linolenic acids would have applications for replac-
ing drying oils such as tung and linseed oil in oil-based paints and coatings (Wilson 2004).
Because of the demand for healthier, more functional vegetable oils, greater emphasis is being placed
on increasing oil content and modifying the fatty acid profile in soybean seed through conventional
breeding and promising biotechnology approaches to target genes that affect oil quantity and quality.
20.3 soyBean oIl quantIty
Typically, soybean seeds contain approximately 20% oil on a dry weight basis (Wilson 2004).
Crude oil contains various glycerolipids, primarily phospholipids, diacylglycerol, and triacylglyc-
erol. Triacylglycerol is the main component of the oil. Phospholipids such as phosphatidylcholine,
