Bitter almond oil

Chemical properties

Bitter almond oil (free from hydrogen cyanide) contains benzaldehyde as its main component. Benzaldehyde does not occur as such in the plant, but is formed, together with hydrogen cyanide, by the hydrolytic cleavage of the glycoside amygdalin.
Amygdalin is present in bitter almonds, the seeds of Prunus dulcis var. amara (DC.) Buchheim, and ripe apricot kernels, Prunus armeniaca L. (Rosaceae).The press cake, which remains after removal of the fatty oils, is macerated with water and left to stand for several hours, after which the “essential oil” is separated by steam distillation. The crude oil contains 2–4% hydrogen cyanide, which is removed by washing with alkaline solutions of iron(II) salts. Subsequent redistillation yields an oil free from hydrogen cyanide. It is a colorless to slightly yellow liquid with an intense, almond-like, cherry aroma and a slightly astringent, mild taste.
d²⁵₂₅ 1.025–1.065; n²⁰_D 1.5350–1.5550; acid value: max. 8; solubility: 1 vol inmax. 6 vol 50% ethanol. HCN content: <0.01%; benzaldehyde content by GC: min. 98%.
Bitter almond oil is used almost exclusively in natural aroma compositions.

Chemical properties

Bitter almond has an intense, almond-like, cherry aroma with a slightly astringent, moldy taste. The term bitter almond refers to the essential oil obtained by steam distillation of the partially de-oleated press-cake of kernels from any of the following: bitter almond (P. amygdalus), apricot (P. armeniaca) and peach (P. persica). The kernels from these and other such fruits contain the glucoside amygdalin, which on enzymatic hydrolysis yields benzaldehyde and HCN. The distilled oil must be rendered free of HCN (prussic acid) prior to its marketing as a flavor ingredient. Very little essential oil is currently made exclusively from bitter almonds or other fruit kernels; specially purified benzaldehyde is often used in its place

Physical properties

Oil intended for use as a flavor ingredient is treated to remove traces of HCN by precipitation as insoluble calcium ferrocyanide.

Definition

Volatile oil from Amygdalin-contg. Prunus species.

Essential oil composition

Bitter almond oil is obtained by first cold-expressing the fixed oils from the comminuted kernels, after which the press-cake is macerated in about 10 parts of water for 12 to 20 hours to effect the enzymatic hydrolysis of amygdalin. The mixture is then steam distilled to yield about 0.5 to 0.7% of the essential oil. Bitter almonds are rarely used because the yield of oil is only 0.6%. Apricot kernels yield 1.2% of oil and are the preferred starting material. The major components of the oil are typically 97.5% benzaldehyde (bitter almond) and 2% hydrogen cyanide (bitter almond).