Vitamin C

Vitamin C(ascorbic acid) is the most important therapeutic constituent in sea buckthorn berry, as it acts as an antioxidant and supports the integrity of the cell membrane. It has been found in practically all parts of the sea buckthorn plant: in berries juice (11.6–13.0 g/kg), in seeds (1.5 g/kg), and in leaves (up to 3.7 g/kg).

In H. rhamnoides, extensive variations of ascorbic acid were found between different shrubs, populations, and subspecies. The concentration of ascorbic acid varies from 0.3 to 3.1 g/kg berry in the European rhamnoides subspecies, from 0.4 to 3 g/kg berry in Russian varieties belonging to the mongolian subspecies, from 4.6 to 13.3 g/kg berry in the fluviatilis subspecies and from 2 to 25 g/kg berry in the Chinese sinensis subspecies.

The vitamin C content in sea buckthorn fruits is 5 to 100 times higher than most other berries or vegetable crops independently of Hippophaë species. Therefore, the ascorbic acid content in sea buckthorn was found to be 20 times higher than that of hawthorn, 3 times higher than in kiwi, 6 times higher than in citrus, 80 times higher than in tomatoes, and 200 times higher than in apples.

Sea buckthorn berries do not contain ascorbate oxidase, the enzyme responsible for the degradation of vitamin C, sea buckthorn products and even dried fruits still contain large amounts of ascorbic acid.

Phenolic Compounds

The whole plant of sea buckthorn—berries, roots, leaves, stems and branches—contain various kinds of phenolics, including flavonoids, phenolic acids, and hydrolysable tannins. Sea buckthorn extract has a total polyphenol content of 140.14 ± 6.64 mg GAE/g dry weight.

A total of 15 phenolic compounds, phenolic acids, flavones, flavonol-monoglycosides, and flavonol-diglycosides, were identified only in the free fractions of all sea buckthorn subspecies by HPLC. Of these, flavonol-diglycosides were predominant: 233 ± 46 mg/100 g dry weight, followed by flavonol-monoglycosides, phenolic acids and flavones (147 ± 24 mg/100 g dry weight, 62.9 ± 23.4 mg/100 g dry weight and 30.9 ± 5.5 mg/100 g dry weight, respectively).

Flavonoids are the most common polyphenols found in food, especially their glycosides, which form the largest group of antioxidants found in nature. Their concentration in sea buckthorn fruits is several times higher than the content recorded in other high-flavonoid plants such as hawthorn, cornelian cherry, wild grown European blackberry, blackthorn or dog rose, mulberry, pomegranate, red raspberries, and blueberry.

Flavonol glycosides form the most concentrated class of phenolic compounds in sea buckthorn. They are found mainly in glycosylated forms of the aglycones of isorhamnetin, quercetin, myricetin, and kaempferol. The most abundant flavonoid compounds in sea buckthorn are isoramnetin glycosides and quercetin derivatives, the latter being the most significant in terms of quantity. It has been shown that flavonol glycosides may play an important role in the prevention and management of chronic diseases such as cancer, diabetes, and cardiovascular disease.

Additionally, to the benefits to human health, the composition and flavonol glycosides content of sea buckthorn may influence the sensory perception of sea buckthorn products. Consequently, the composition and content of flavonol glycosides are among the most important indicators of the quality and therapeutic potential of sea buckthorn berries.

Regarding the phenolic acid content of sea buckthorn berry, the salicylic acid is the dominating phenolic acid in sea buckthorn fruits. Its concentration ranged from 21 up to 47 mg/kg dry weight of fruits depending on the variety, followed by p-coumaric acid (1.4–9.8 mg/kg dry weight), caffeic acid (concentration up to 6.7 mg/kg dry weight), gallic acid (1.0–4.6 mg/kg dry weight), and vanillic acid (0.5–1.8 mg/kg dry weight).

A different hierarchy of the identified phenolic acids in sea buckthorn were reported. Gallic acid in free form is dominating, with a variable concentration occurring in leaves (79 mg/kg) and berries (16.9 mg/kg), while other phenolic acids such as caffeic acid, p-coumaric acid, and ferulic acid are found in a lower amount in sea buckthorn.

Besides flavonoids and phenolic acids, Hippophaë species contain tannins. Tannins are water-soluble polyphenol compounds found in alkaloids, polysaccharides, and proteins with relatively high molecular weight.

Tannins in sea buckthorn are divided into two groups: hydrolysable and condensed tannins. Gallo- and ellagitannins of monomeric type are the most abundant subgroups of hydrolysable tannins and includes stachyurin, casuarinin, casuarictin, hippophaenin B, strictinin, and isostrictinin.

Condensed tannins typically consist of two or more monomeric (+)-catechin or (-)-epichatechin units (procyanidins), while the other group consist of (+)-gallocatechin or (-)-epigallocatechin units (prodelphinidins). They are present in higher concentrations in sea buckthorn seeds, roots, flowers, green berries, and stems.