11.4 Flaxseed (linseed and linola) oil

Flax crops have been grown for many centuries but originally for the fibres that

can be used as linen textile. Linseed is an alternative name, twist title, for

flax, which points towards the modern uses of the plant seed (Krawczyk 1999).

Both linseed and flax are cultivars ofLinum usitatissimum.Linseed varieties

have shorter (6080 cm high) and thicker stems with more branches compared

with flax (80120 cm). A flax crop produces fewer capsules and smaller seeds

than linseed. Crops grown for seed are termed linseed in India and in the UK,

flax seed in Canada, and oil flax or seed flax in many European countries. The

crops grown for both seed and flax are generally called dual-purpose flax, or flax

grown for fibre flaxseed. The oil content of commonly grown linseed varieties

may vary from 4044%. The content of linolenic acid (18:3), usually above

50%, makes linseed oil an excellent drying oil. This is used principally for nonedible purposes such as in the manufacture of paints, varnishes, linoleum and

printing inks. As discussed below, among the unique features of flaxseed is that

it is a rich source of-3-linolenic acid, plant lignans and dietary soluble fibre.

The whole flaxseed/linseed is edible and is used in baking and confectionery

industries. Moreover, edible flaxseed or linseed oil is sold at health food stores

where its health benefits are recognised.

11.4.1 Flax production and oil composition

Flax is a sub-tropical or cool-to-warm temperature annual crop grown mainly

in Canada, Argentina, India, the US, China, some European countries, and the

former USSR. More than 60 years ago the world production of flaxseed was

around 3.4 million tonnes (Krawczyk 1999) which was more than sunflower

oil at 2.5 million tonnes. Since then, however, world production of flaxseed

has remained between 2 and 3 million tonnes, while the production of other

oilseeds has increased considerably. In 20002001, world production of flaxseed

was 2.34 million tonnes, with Canada the largest producer and largest exporter.

Figures for the production, disappearance and exports/imports of linseed oil are

given in Chapter 1.

Most flax is now grown to make linseed oil. The seeds are usually pressed

and extracted by solvent to yield crude linseed oil which is brown/dark amber

in colour. The colour can be reduced by caustic refining and bleaching. Such

processing also removes gums or phospholipids present in the oil. Table 11.11

lists some characteristics and fatty acid composition of linseed oil from high

linolenic acid varieties ofL. usitatissium. Seed variety and climatic conditions

during maturation both affect the linolenic acid content of the oil. Linseed

oil contains 0.42% of the usual sterols. The predominant sterols, namely-sitosterol, campesterol,5

-avenasterol, and stigmasterol, have been reported

to be 46%, 29%, 13% and 9% respectively (Gunstoneet al. 1994). Linseed oil

contains 440588 mg/kg of tocopherol,-tocopherol being most predominant

(Firestone 1999). The high levels of-linolenic acid (18:3n-3) make the oil

oxidise quickly. When the oil is used for food purposes a paint-like flavour is

imparted to food products in a very short time. Therefore, edible flaxseed oil

must be stored under cold, oxygen-free, light-free conditions and be protected

by an addition of suitable antioxidant formulation containing metal chelators

and oxygen quenchers. Recently Nag (2000) showed that incorporation of oilsoluble capsicum extract slowed considerably the rate of oxidation of the oil. The

colour of the stabilised oil was bright red but the product flavour was acceptable

when used as a salad oil. Traditionally, the oil for human consumption is

extracted by a cold-press technique. Depending upon the applications, the oil is

then mildly refined and perhaps deodorised at low temperature for encapsulation

and blending with other healthful oils.

11.4.2 Edible uses of flaxseed and its oil

Edible flaxseed oil is not generally used as a food oil due to its very low oxidative

stability. However, ground or whole flaxseed is edible and is used in many bakery

and confectionery products to enhancing nutritional value by supplying a good

source of3 essential fatty acid,-linolenic acid. Flaxseed contains about 25%

fibre, of which 2040% is soluble fibre (Vaisey-Genser 1994) that may play an

important role in lowering plasma cholesterol. Flaxseed is also a rich source of

plant lignans thought to be protective against hormone related cancers of the

breast, prostrate and colon. Flaxseed and its oil is sold at many health food stores

because of these benefits. Carter (1993) reviewed usage and health aspects of

flaxseed and flaxseed oil with special emphasis on their high fibre andn-3 fatty

acid contents, and their potential use in baked goods and other foods. Cunnane

and Thompson (1995) have discussed various nutritional characteristics and

health benefits of flaxseed and its oil. After oil extraction, flax cake or meal is

usually sold for cattle feed. Krawczyk (1999) reported that whole flaxseed can

be used as a dairy feed to promote the production of conjugated linoleic acid

in milk (Dhimanet al. 2000) and in milk fat (Chouinard et al. 2001). Flaxseed

can also be used in chicken feed to produce eggs high in3 fatty acids (Suzuki

et al. 1994; Stroh et al. 1997). The egg protects against oxidative deterioration

of-linolenic acid during its shelf life and3 enriched eggs fetch a premium

at the grocery store.

Most flaxseed destined for human consumption is sold in health food stores

or in capsule form as a dietary supplement. The volume of organically grown

flax is increasing to meet the demands of the typical health food consumer.

The edible use of linseed and its oil containing health beneficial components is

expected to rise in the future.