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Processing Canola Oil
Canola is an oilseed crop that was developed from
traditional rapeseed by Canadian plant breeders during the 1970's. It
is grown widely across Canada, several European countries, and Australia,
and to a lesser extent in the United States. Canola is distinguished
from traditional rapeseed by the greatly reduced levels of the fatty
acid, erucic acid and anti-nutritional compounds called glucosinolates.
These alterations have led to the widespread use of
canola oil in Canada and today it is the most popular all-purpose vegetable
oil. Canola oil is sold as a salad and frying oil and is also used in
margarines, shortenings and in prepared foods that contain vegetable
oil (such as baked goods, potato chips, french fries, etc.). Canola
oil accounted for approximately 78% of total Canadian production of
edible oils in 1996 (Statistics Canada, 1996).
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In terms of domestic production of food products, canola oil accounts for approximately 88% of salad and cooking oils, 71% of shortening oils, and 53% of margarine oils. Canola oil is used for similar purposes in the United States, where it represents 7% of total vegetable oil use. |
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Canola oil is the preferred oil for use in both countries
because it is the oil lowest in saturated fats. Canola meal is the by-product
of canola oil processing. It is used as a high-protein feed ingredient
in the rations of poultry, swine, cattle and fish.
These food and feed applications are possible through
strict procedures used in the processing of canola seed into oil and
meal. This document describes the processing methodologies that are
used by the canola industry to produce high quality oil and meal products.
The production of edible vegetable oils including
canola oil involves two overall processes, mechanical pressing and extraction,
and further processing to remove impurities. The techniques used are
similar for most vegetable oils produced from the seeds of plants. The
crushing and extraction processes utilized by the canola industry today
produce very little change to the fatty acid profile of the oil and
the nutritional qualities of the meal.
The majority of canola seed is grown by Canadian farmers
as a commodity crop, meaning that canola seed is commingled and not
separated by variety or other specific traits. Following harvest, canola
seed is purchased by Canadian and American processors on the basis of
grading standards set by the Canadian Grain Commission and, in the U.S.,
by the National Institute of Oilseed Processors. A number of criteria
are used to grade canola seed, including the requirement that the seed
must meet the canola standard with respect to erucic acid and glucosinolate
levels.
Canola Seed Cleaning
Graded seed is cleaned by a number of different methods
including air aspiration, indent cylinder cleaning, sieve screening,
or a combination of these. Cleaning ensures that the seed is free of
extraneous plant and other foreign material which is referred to in
the industry as "dockage". Seed generally contains less than
2.5% dockage following the cleaning process. Seed that has been cleaned
is ready for subsequent export or for crushing into canola oil and meal.
Canola Seed Preconditioning
Seed which will be processed for oil and meal is preconditioned
using mild heat treatment, and moisture is then adjusted to improve
subsequent oil extraction.
Canola Seed Processing
Following preconditioning, canola seed is next crushed
and flaked and then heated slightly. These processes help to maximize
oil recovery. The canola flakes are then "prepressed" in screw
presses or expellers to reduce the oil content from about 42% in the
seed (on an 8% moisture basis) to between 16-20%. Screw pressing also
compresses the flakes into more dense cakes (called "press cake")
which facilitates oil extraction.
Canola Oil Extraction
Press cake which results from seed processing is next
subjected to one of two types of oil extraction to remove much of the
remaining oil. Oil may be extracted using either hexane ("solvent")
extraction or by "cold-pressing" (also referred to as "expeller
pressing"). The end-market into which the oil is sold generally
dictates which form of extraction will be used. Hexane is the extraction
medium used for the bulk of canola oil which is sold into the commodity
grocery chain market as well as to the food industry. Cold-pressed canola
oil represents a much smaller volume sold to consumers and is generally
marketed in specialty food stores. Both extraction processes result
in an oil essentially bland in taste, light yellow in color, and with
excellent nutritional and stability properties.
Hexane Extraction of Canola
Hexane extraction reduces the oil content of the press
cake to very low levels. Oil recovery from canola seed is approximately
96% when this form of extraction is used. This is accomplished by maximizing
contact of the hexane with the press cake through a series of soakings
or washings. Residual hexane in the extracted press cake and oil is
easily removed by evaporation at low temperature. Solvent residues in
oils and meals, when produced in accordance with good manufacturing
practice, can be said to be truly insignificant.
Canola Oil Refining
The oil which is produced during the extraction process
is referred to as "crude oil" because it contains various
compounds which must be removed to ensure a product with good stability
and shelf-life. These impurities include phospholipids, mucilaginous
gums, free fatty acids, color pigments and fine meal particles. Different
methods are used to remove these by-products including water precipitation
or organic acids in combination with water. Once removed, these by-products
are added to the canola meal fraction in order to increase its feeding
value (energy) and make it an even more nutritious product.
Following water precipitation and/or organic acid
processing, the oil will still contain color compounds which, if not
removed would make it unattractive to the consumer and also reduce its
stability. These compounds are extracted through a process called bleaching.
In contrast to what may be implied by the term, bleaching does not involve
the use of harsh chemicals. Instead, during the bleaching process, the
oil is moved through a natural, diatomaceous clay to remove color compounds
and other by-products.
Deodorization is the final step in the refining of
all vegetable oils, including canola. Deodorization involves the use
of steam distillation with the objective being the removal of any residual
compounds which, if retained, could impart an adverse odor and taste
to the oil. The oil produced is referred to as "refined oil".
Further Processing of Canola Products
Refined canola oil is utilized in a large variety
of edible oil products. Generally, no further processing is required
for canola oil used as a liquid product for salads, dressings and home
frying. The refined oil is sold under a number of brand names for both
household and industrial purposes. A special process called hydrogenation
is used in the production of margarine, shortening and other specialized
products. Hydrogenation solidifies the oil and therefore greatly increases
the range of products in which it can be used. As a rule, the more "solid"
a product is, the greater has been the degree of hydrogenation.
Canola oil may also be processed into more solid products
using a method called interesterification. Interesterification involves
mixing canola oil with other oils that are more solid by nature, including
palm kernel oil. Special processing parameters are utilized and result
in a semi-solid product which does not need to be hydrogenated.
Cold Pressing of Canola
The production of cold pressed canola oil involves
essentially the same steps as those used in hexane extraction. The most
significant difference is that the hexane extraction step is omitted
and the oil is removed primarily through mechanical pressing. In addition,
the temperature of the cake during the mechanical pressing of the oil
from the seed is controlled at 60 degrees C by water cooling. A drawback
to cold pressing is that the recovery of oil is lower than from hexane
extraction. This is because the mechanical pressing of the cake is less
effective at low temperatures. Oil recovery when using cold-pressing
techniques most often ranges between 75% to 85 %. The price of cold
pressed canola oil tends to be slightly higher because of the lower
recovery of oil. Cold pressed canola oil is generally sold in bottled
form directly to consumers and is usually not used in further food processing.
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