The Bark of the Spruce Picea jezoensis Is a Rich Source of Stilbenes

Abstract

Stilbenes are plant phenolic secondary metabolites that show beneficial effects on human health and possess high antifungal activity against plant pathogens. Currently, a search for plant sources with high stilbene levels is relevant, since stilbene content in various plant species can vary substantially and is often at a low level. In this paper, the bark and wood of Picea jezoensis were analyzed for the content and composition of stilbenes and compared with other known stilbene sources. The HPLC-MS analysis of P. jezoensis bark and wood extracted with different solvents and at different temperatures revealed the presence of 11 and 5 stilbenes, respectively. The highest number of stilbenes of 171 and 229 mg per g of the dry weight (mg/g DW) was extracted from the bark of P. jezoensis using methanol or ethanol at 60 °C for 2 h. Trans-astringin, trans-piceid, and trans-isorhapontin prevailed over other stilbenoids (99% of all detected stilbenes). The most abundant stilbene was trans-isorhapontin, reaching 217 mg/g DW or 87% of all stilbenes. An increase in the extraction time from 2 to 6 h did not considerably increase the detected level of stilbenes, while lower extraction temperatures (20 and 40 °C) significantly lowered stilbene yield. The content of stilbenes in the P. jezoensis bark considerably exceeded stilbene levels in other stilbene-producing plant species. The present data revealed that the bark of P. jezoensis is a rich source of stilbenes (primarily trans-isorhapontin) and provided effective stilbene extraction procedures.

Keywords: Picea jezoensis; astringin; bark; isorhapontin; piceatannol; piceid; resveratrol; stilbenes.

Figure 1

Comparison of HPLC-UV chromatographic profiles for the methanolic extracts of spruce bark (a) and needles (b) recorded at 310 nm. Spruce bark and needles were collected in winter. Trans-astringin (1, retention time 18.0 min), cis-astringin (2, 20.2 min), trans-piceid (3, 20.8 min), trans-isorhapontin (4, 21.9 min), trans-piceatanol (5, 22.6 min), cis-piceid (6, 23.9 min), cis-isorhapontin (7, 24.5 min), trans-resveratrol (8, 26.5 min), trans-isorhapontigenin (9, 28.8 min), cis-resveratrol (10, 29.7 min), cis-isorhapontigenin (11, 20.2 min).

Figure 2

Hypothetical biosynthetic pathway for stilbene formation in Pinaceae [25]. Circles with dotted lines depict 11 stilbenes detected in the needles of spruce Picea jezoensis: trans- and cis-astringin [1,2], trans- and cis-piceid [3,6], trans- and cis-isorhapontin [4,7], trans-piceatannol [5], trans- and cis-resveratrol [8,10], and trans- and cis-isorhapontigenin [9,11]. Trans-astringin [1], trans-piceid [3], and trans-isorhapontin [4] marked with thick dotted lines because the content of these compounds is much higher than the other stilbenes. The peak numbers for detected stilbenes in square brackets are shown as in Figure 1.