Environmental Engineering Reference
In-Depth Information
and is now grown as a vegetable or an oil seed crop in China, India, Sweden, Finland, and Canada
(Rakow 2004), and it is also found as a weed in the United States. Spring/summer and winter annual
cultivars have been developed.
The
Brassica
species most widely grown for its seed oil is
B. napus
L. (also known as rapeseed,
oilseed rape, swede rape, and Argentine rape) which is considered to have its origin either in the
Mediterranean or western and northern Europe. There are both winter and spring/summer annual
forms of
B. napus
. Winter type
B. napus
is the main rapeseed crop in Europe, parts of China, and
the eastern United States. Both summer and winter forms are cultivated in Europe and Canada and
only the summer form is grown in Australia.
The current rapeseed varieties grown in the United States and Canada are cultivars of either
B. napus
or
B. rapa
species, the former being cultivated on the majority of hectares. Both the species
have been used to breed spring or winter varieties and for industrial or edible oil markets. Industrial
rapeseed, along with its wild ancestors, contains long chain fatty acids that limit its acceptability
as an edible oil. High levels of glucosinolates (500 μM/g) give rapeseed oil an unacceptable sharp
taste and are responsible for its thyroid disrupting properties. Erucic acid, a long chained fatty acid
(C22:1) is present in the oil, often in concentrations reaching 50-60% of total seed oil.
To address the antinutritional aspects of rapeseed oil, and to increase the value of the protein-
rich meal remaining after oil extraction, edible rapeseed varieties were developed by Canadian
plant breeders in 1974. They contained very low levels of glucosinolates (30 μ mol/g) and of erucic
acid (about 1%). These new varieties were termed “Canola,” which is an acronym for Canadian Oil
Low Acid (Steffansson and Downey 1995). As in the case of rapeseed varieties, spring and winter
canola-quality cultivars have been bred from both
B. rapa
and
B. napus.
Canola therefore refers to
B napus
and (less commonly)
B. rapa
varieties that are low in both glucosinolates and erucic acid.
Within each species, the edible oil, canola-quality cultivars are visually indistinguishable from the
industrial oil, rapeseed varieties.
18.2.2 f
atty
a
cid
p
rofilES
The energy in seed oils is stored in the form of triacylglycerols (TAG), which are a source for
carbon storage and synthesis of fatty acids (FA). The FA present in seed oils are diverse in their
chemical composition and vary based on the length of carbon chain (C12 to C24) and their degree
of saturation/desaturation (presence of 1 to 3 double bonds). They are generally denoted by their
carbon chain length followed by the number of double bonds. On the basis of this system of notation,
FA are classified as saturated FA (SFA, e.g., C16:0 and C18:0), monounsaturated FA (MUFA, e.g.,
C18:1 and C20:1), polyunsaturated FA (PUFA, e.g., C18:2, C18:3), and very long-chain FA (VLCFA,
e.g., C22:1 and higher). It is the profile of FA in a particular oil which determines its nutritional
quality or its industrial value. For example, the FA composition of a superior vegetable oil for
human consumption is expected to contain a high ratio of MUFA/SFA, a good proportion (at least
5:1) of PUFA and no VLCFA (FAO/WHO). On the other hand, the oils with a high percentage (20-
50%) of VLCFA such as C20:0, C22:0, and C24:0 are desirable for industrial use to manufacture
lubricants (McVetty et al. 2008).
Brassica/rapeseed oil is composed of FA with varying carbon chain lengths and levels of
desaturation. Typical FA profiles for cultivars of
B. napus
,
B. juncea
, and
B. rapa
(Shahidi 1990;
Scarth and Tang 2005) are approximately 5% C16:0 (palmitic acid), 1% C18:0 (stearic acid), 15%
C18:1 (oleic acid), 14% C18:2 (linoleic acid), 9% C18:3 (linolenic acid), and 45% C22:1 (erucic acid).
A comparison (McVetty and Scarth 2002) of the FA profiles of rapeseed and mustard oils with an
FA composition of selected naturally occurring vegetable oils (soybean, sunflower, corn, peanut,
palm, and olive) reveals that the composition of Brassica oil is genetically more variable than any of
the other vegetable oils included in the study. This variability in the composition of Brassica oil has
been successfully manipulated to produce cultivars with specific FA profiles in the seed oil tailored
for specific end uses. A classic example of this was the development of canola from rapeseed where
