1. FATTY ACID OCCURRENCE AND DISTRIBUTION
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The fruit-coat fats vary in consistency from oils liquid at ordinary
temperature, such as olive oil, to hard waxlike materials, such as
stillingia and sumach tallows, which do not melt below about 50°.
c. Seed Fats. The classification of the seed fats on the basis of their
chief component fatty acids, as outlined by Hilditch (3), is followed
in this section. This leads in many instances to the grouping together
of members of the same family. Broadly, fats which contain the typical
acids, viz., oleic, palmitic, linoleic, and linolenic acids are first considered and arranged in descending order of mean unsaturation; this
gives groups corresponding to drying, semidrying, and nondrying oils.
Subsequently, fats containing a characteristic fatty acid, other than
those mentioned above, are grouped together under the fatty acid concerned. In this system it is convenient to list the names of families
which include species whose fats fall into line with the fatty acids
upon which the classification is based. This does not, however, necessarily imply that all the species within the families mentioned fall into
the classification thus arranged. In some cases the same family will
appear under two different classifications as members within the family
fall into separate categories. Thus the Ulmaceae family appears under
the linoleic acid-rich fats as well as under fats which contain n-decanoic
(capric) acid as the main constituent.
(1) Seed fats with linoleic (oleic) and linolenic acids as major
components; minor components, palmitic and stearic acids.
(a) Linolenic acid-rich seed fats: In this group the following families are represented: Gymnosperms—Coniferae; Angiosperms—Maracaceae, Celastraceae, Aquifoliaceae, Labiatae, Valerianaceae, Oenotheraceae, Linaceae, Elaeagnaceae, and Rhamnaceae.
The best-known example of the linolenic acid-rich group is linseed
(Linum usitatissimum) oil (Linaceae), which contains saturated (mainly palmitic) 6-16%, oleic 13-36%, linoleic 10-25%, and linolenic 30-60%,
acids. In the various families with linolenic acid-rich seed oils, the
linolenic acid content does not usually exceed 50% except in the
Labiatae. A notable example here is perilla (Perilla ocimoides) seed
oil with up to 70% linolenic acid. Although the seed fats of the families
listed are essentially composed of palmitic, oleic, linoleic, and linolenic
acids, in the seed oil of the evening primrose (Oenothera biennis), a
species of Oenotheraceae, linolenic (octadeca-9,12,15-trienoic) acid itself is absent. However, an isomer of linolenic acid, octadeca-6,9,12trienoic acid, occurs (234, 2S5).
(b) Mainly linoleic acid-rich seed fats: In this group the saturated
acids, mainly palmitic, form 4-20% of the total fatty acids. Linolenic
45
The fruit-coat fats vary in consistency from oils liquid at ordinary
temperature, such as olive oil, to hard waxlike materials, such as
stillingia and sumach tallows, which do not melt below about 50°.
c. Seed Fats. The classification of the seed fats on the basis of their
chief component fatty acids, as outlined by Hilditch (3), is followed
in this section. This leads in many instances to the grouping together
of members of the same family. Broadly, fats which contain the typical
acids, viz., oleic, palmitic, linoleic, and linolenic acids are first considered and arranged in descending order of mean unsaturation; this
gives groups corresponding to drying, semidrying, and nondrying oils.
Subsequently, fats containing a characteristic fatty acid, other than
those mentioned above, are grouped together under the fatty acid concerned. In this system it is convenient to list the names of families
which include species whose fats fall into line with the fatty acids
upon which the classification is based. This does not, however, necessarily imply that all the species within the families mentioned fall into
the classification thus arranged. In some cases the same family will
appear under two different classifications as members within the family
fall into separate categories. Thus the Ulmaceae family appears under
the linoleic acid-rich fats as well as under fats which contain n-decanoic
(capric) acid as the main constituent.
(1) Seed fats with linoleic (oleic) and linolenic acids as major
components; minor components, palmitic and stearic acids.
(a) Linolenic acid-rich seed fats: In this group the following families are represented: Gymnosperms—Coniferae; Angiosperms—Maracaceae, Celastraceae, Aquifoliaceae, Labiatae, Valerianaceae, Oenotheraceae, Linaceae, Elaeagnaceae, and Rhamnaceae.
The best-known example of the linolenic acid-rich group is linseed
(Linum usitatissimum) oil (Linaceae), which contains saturated (mainly palmitic) 6-16%, oleic 13-36%, linoleic 10-25%, and linolenic 30-60%,
acids. In the various families with linolenic acid-rich seed oils, the
linolenic acid content does not usually exceed 50% except in the
Labiatae. A notable example here is perilla (Perilla ocimoides) seed
oil with up to 70% linolenic acid. Although the seed fats of the families
listed are essentially composed of palmitic, oleic, linoleic, and linolenic
acids, in the seed oil of the evening primrose (Oenothera biennis), a
species of Oenotheraceae, linolenic (octadeca-9,12,15-trienoic) acid itself is absent. However, an isomer of linolenic acid, octadeca-6,9,12trienoic acid, occurs (234, 2S5).
(b) Mainly linoleic acid-rich seed fats: In this group the saturated
acids, mainly palmitic, form 4-20% of the total fatty acids. Linolenic