G5 Doctoral dissertation (article)
Non-volatile Bioactive and Sensory Compounds in Berries and Leaves of Sea Buckthorn (Hippophaë rhamnoides)




List of Authors: Ma. Xueying
Publisher: University of Turku
Place: Turku
Publication year: 2018
ISBN: 978-951-29-7378-1
eISBN: 978-951-29-7379-8

Abstract

Sea buckthorn (Hippophaë rhamnoides L., SB) is regarded as a raw material of high economic value and a source of many health-related bioactive compounds, such as flavonol glycosides (FGs), proanthocyanidins (PAs) and ethyl β-Dglucopyranoside (EG) in berries and ellagitannins (ETs) in leaves. These phenolic compounds are also well known components in various foods inducing astringent and bitter sensations. Ethyl β-D-glucopyranoside, an alkylated glucose, is among the major chemotaxonomic characteristics in SB berries. 

The aims of the current work were: 1) To qualitatively and quantitatively analyze FGs, PAs in SB berries and purees, as well as FGs and ETs in SB leaf and leaf tea-type beverages; 2) To determine the effects of genetic background, growth sites and processing methods on the contents and compositions of these compounds; 3) To investigate the roles of FGs, PAs and EGs in the sensory quality of SB purees/juices; 4) To study the antioxidant activities (AAs) in leaf tea-type infusions, the correlations with AAs, FGs and ETs. 

Twenty-six flavonol glycosides with isorhamnetin and quercetin as the major aglycones were found in the wild SB (ssp. sinensis) berries from China and cultivated berries (ssp. mongolica) from Finland and Canada. The contents of FGs varied from 23 to 250 mg/100 g fresh berries, which were significantly higher in ssp. sinensis than in ssp. mongolica. The berries of ‘Oranzhevaya’ and ‘Prevoshodnaya’ had the lowest (23 mg/100 g) and the highest content of FGs (80 mg/100 g), respectively. The samples from Kittilä (North Finland) had higher levels of most FGs than those from Turku (South Finland) and Québec (Canada). Among the ssp. sinensis berries, the berries from Sichuan had the highest contents and unique profiles of FGs. Increasing trends were detected in the contents of most FGs as the altitude increased and as the latitude decreased. 

The role of ethyl β-D-glucopyranoside was investigated in the sensory profiles of SB juices of ‘Terhi’ and ‘Tytti’. The taste threshold of pure EG was estimated in water solution as 1.1 ± 1.3 g/L, and the suprathreshold aqueous EG solution (5.0 g/L) was perceived mainly as bitter. Addition of EG increased bitterness of SB juice, which correlated with the EG content, as well as with the ratios of EG/acids and EG/sugars. The roles of FGs and PAs were also investigated in purees of six SB cultivars. The sensory profiles of the purees were dominated by intense sourness due to abundant malic acid, followed by astringency and bitterness. Malic acid and isorhamnetin glycosides related strongly to the astringency, whereas PA dimers, PA trimers and quercetin glycosides had less influence. Moreover, the acids/phenolic compounds ratios were more important predictors of bitterness than the individual variables alone. 

Composition and contents of flavonol glycosides and ellagitannins as well as antioxidant activities were investigated in tea-type infusions processed from sea buckthorn leaves using different drying methods. These infusions had high content of phenolic substances together with associated strong antioxidant activities, were considerably acceptable for consumers. Isorhamnetin-3-Oglucoside- 7-O-rhamnoside, isorhamnetin-3-O-rutinoside and kaempferol-3-Ohexoside- 7-O-rhamnoside were the three major FGs, and stachyurin and casuarinin were the most abundant ETs in all the samples. Significant differences were found in the contents of most ETs between the infusions of ‘Terhi’ and ‘Tytti’ (p < 0.05). The ET contents varied significantly among the different processing methods, whereas less effect was seen on the FGs contents. Thermal processing decreased the antioxidant activities of the infusions. Additionally, significant contents of phenolic compounds were left in the leaf residues after the hot water extractions.


Last updated on 2019-20-07 at 06:50