Rubus coreanus (Rosaceae) – Korean black raspberry (bokbunja)

Rubus coreanus, commonly known as Korean black raspberry and in Korea as bokbunja, is a bramble-like shrub of the genus Rubus, native to East Asia, particularly Korea, Japan and China. It belongs to the Rosaceae family and is traditionally associated with the production of fruit wines and a wide range of medicinal uses in Korean traditional medicine. The plant grows as an arching, cane-forming shrub, often spiny, capable of forming dense thickets along forest margins, slopes and hilly areas in temperate humid climates. The leaves, usually compound and serrated, resemble those of other raspberries, while the white to pinkish flowers, borne in terminal inflorescences, precede the formation of the characteristic dark fruits.

Morphologically, the fruit of Rubus coreanus is an aggregate of drupelets, as in other raspberries and blackberries, which at full ripeness acquires an intense black-purple colour due to its high content of anthocyanins. The fruits generally ripen between late spring and early summer and are consumed fresh, dried or used as raw material for the production of bokbunja-ju, the traditional Korean black raspberry wine obtained by fermenting the fruits with water (sometimes with the addition of rice or other ingredients). This beverage plays an important role in Korean food culture and is often associated, in folk tradition, with beneficial effects on vitality and certain aspects of male reproductive function, though such attributions should be viewed primarily in a historical and cultural context.

From an ecological standpoint, Rubus coreanus behaves as a light-demanding species typical of secondary and marginal habitats: it colonises clearings, well-drained slopes and disturbed sites, contributing to soil cover and providing an important food resource for many frugivorous animals, particularly birds and small mammals. Zoochorous seed dispersal favours the formation of new populations, while the ability to produce basal shoots and to spread vegetatively allows the species to maintain long-lived clumps and to play a significant role in the dynamics of rural landscapes.

The main scientific interest in Rubus coreanus lies in its phytochemical profile. The fruits are rich in polyphenols, with a marked predominance of anthocyanins (especially cyanidin and delphinidin derivatives), along with ellagitannins, ellagic acid, flavonoids and other phenolic compounds. These constituents confer a high in vitro antioxidant capacity and are the subject of numerous studies aimed at assessing their potential role in modulating processes related to oxidative stress, inflammatory responses and energy metabolism.

Experimental studies in cell and animal models have documented possible anti-inflammatory, anti-ulcer, hypoglycaemic activities and effects on adipose tissue modulation. Extracts obtained from unripe and ripe fruits of Rubus coreanus have been investigated for their influence on signalling pathways involved in immune responses, gastric mucosal protection, glucose metabolism regulation and lipid accumulation. Some works have reported, for example, effects on parameters associated with “browning” of white adipose tissue and inhibition of lipid peroxidation in experimental systems, findings that fuel interest in this species in the context of research on metabolic disorders and chronic diseases.

It is, however, essential to emphasise that most of this evidence comes from preclinical studies, conducted mainly in vitro or in animal models, often using standardised extracts or purified fractions (for example rich in anthocyanins or ellagic acid). Their direct translation into clinical practice or human nutrition therefore requires great caution. In the food realm, the consumption of traditional products based on Rubus coreanus (such as bokbunja wine or processed fruits) usually falls within the framework of gastronomic and cultural use, compatible with a balanced diet. By contrast, the use of dietary supplements or high-titre extracts raises open questions regarding standardisation, dosage, long-term safety and interactions with ongoing pharmacological therapies.

Within Korean traditional phytotherapy, Rubus coreanus has historically been attributed multiple uses that involve not only the fruits but also seeds, leaves and roots. Classical sources describe the use of unripe fruits for conditions related to the reproductive sphere and glucose metabolism, whereas ripe fruits are mentioned in relation to respiratory complaints and support of liver and kidney functions. While these indications are significant from an ethnobotanical and historical perspective, they must today be assessed through the lens of modern evidence-based criteria, clearly distinguishing between traditional descriptions and data substantiated by controlled clinical trials.

From an agronomic and technological point of view, Rubus coreanus is the subject of breeding programmes aimed at improving yield, anthocyanin content, aroma profile and stability of bioactive compounds in processed products, especially in black raspberry wines. Studies have examined the impact of fruit ripeness, pedoclimatic conditions and winemaking techniques on polyphenol content and on the sensory properties of the final products, with the dual aim of optimising both organoleptic quality and the potential functional value of these beverages.

Botanical classification (APG IV system)

Indicative nutritional values per 100 g (fresh fruits of Rubus coreanus)
Values refer to fresh bokbunja-type berries; they may vary with cultivar, growing conditions and ripeness. Figures are adapted from data on Rubus coreanus and closely related black raspberry–type fruits.

At typical serving sizes (about 50–100 g of fresh fruits, juice or processed products), Korean black raspberry provides a moderate energy intake, almost entirely from carbohydrates, together with a relevant amount of dietary fiber and an interesting contribution of vitamin C. From a phytochemical perspective, these fruits are notable for their high content of phenolic compounds, especially anthocyanins.

Lipid profile note

Fresh fruits of Rubus coreanus have an overall low fat content. Saturated fatty acids (SFA) are present only in small amounts; when SFA predominate over unsaturated fats in the overall diet, they are generally considered less favourable for cardiovascular health.

Most of the small lipid fraction is made up of monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA), which are usually regarded as more favourable when they replace part of dietary SFA. In the case of Rubus coreanus, however, the absolute fat intake from typical portions remains modest, and nutritional interest focuses primarily on fiber, vitamin C and phenolic compounds rather than on lipids.

Plant Characteristics:
Rubus coreanus is a deciduous, perennial shrub characterized by its arching stems and compound leaves. The plant typically grows 1 to 2 meters in height and has thorny stems. The leaves are palmate with serrated edges. The flowers are white to pink and are usually small and clustered. The fruit, known for its deep color and distinctive flavor, is an aggregate of drupelets, typically harvested in late summer to early autumn.

Chemical Composition and Structure:
The fruit of Rubus coreanus is rich in various bioactive compounds:

Anthocyanins: These pigments contribute to the fruit's dark color and have antioxidant properties.

Polyphenols: Including flavonoids and phenolic acids, which provide antioxidant, anti-inflammatory, and antimicrobial benefits.

Vitamins: High in Vitamin C and other essential vitamins.

Minerals: Contains significant amounts of potassium, calcium, and magnesium.

Dietary Fiber: Promotes digestive health.

How to Cultivate It:

• Climate: Prefers temperate climates with well-defined seasons. It requires a cold period to induce dormancy.
• Soil: Thrives in well-drained, loamy soils with a slightly acidic to neutral pH.
• Sunlight: Requires full sun to partial shade.
• Watering: Regular watering is essential, particularly during dry periods, but overwatering should be avoided to prevent root rot.
• Pruning: Regular pruning helps maintain plant health and productivity by removing dead or diseased wood and encouraging new growth.

Uses and Benefits:

• Culinary Uses: The fruit is used in various culinary applications, including jams, juices, wines, and traditional Korean dishes.
• Medicinal Uses: In traditional medicine, it is used for its antioxidant and anti-inflammatory properties. It is believed to aid in digestion and improve overall vitality.
• Cosmetic Uses: Extracts are used in skincare products for their antioxidant and anti-aging effects.

INCI Functions:

Skin conditioning agent. It is the mainstay of topical skin treatment as it has the function of restoring, increasing or improving skin tolerance to external factors, including melanocyte tolerance. The most important function of the conditioning agent is to prevent skin dehydration, but the subject is rather complex and involves emollients and humectants that can be added in the formulation.

Antioxidant agent. Ingredient that counteracts oxidative stress and prevents cell damage. Free radicals, pathological inflammatory processes, reactive nitrogen species and reactive oxygen species are responsible for the ageing process and many diseases caused by oxidation.

Applications:

• Food Industry: Used as a flavoring agent and in the production of beverages and preserves.
• Pharmaceutical Industry: Explored for its potential in developing supplements and functional foods due to its high antioxidant content.
• Agriculture: Cultivated for both commercial and ornamental purposes.

Environmental and Safety Considerations:

• Invasive Potential: Rubus coreanus can become invasive in non-native environments, potentially outcompeting local flora.
• Pests and Diseases: Susceptible to pests such as aphids and diseases like powdery mildew. Proper management practices are necessary to mitigate these issues.
• Safety: Generally considered safe for consumption. However, individuals with allergies to raspberries or related fruits should exercise caution.

References_____________________________________________________________________

Pyeon S, Kim OK, Yoon HG, Kim S, Choi KC, Lee YH, Lee J, Park J, Jun W. Water Extract of Rubus coreanus Prevents Inflammatory Skin Diseases In Vitro Models. Plants (Basel). 2021 Jun 17;10(6):1230. doi: 10.3390/plants10061230. PMID: 34204204; PMCID: PMC8235380.

Abstract. Atopic dermatitis (AD) is a chronic inflammatory skin disease caused by immune hypersensitivity reaction. The cause of AD is unclear, but its symptoms have a negative effect on quality of life; various treatment methods to alleviate these symptoms are underway. In the present study, we aimed to evaluate in vitro antioxidant and anti-inflammatory effects of Rubus coreanus water extract (RCW) on AD. Total phenolic compounds and flavonoid content of RCW were 4242.40 ± 54.84 mg GAE/g RCE and 1010.99 ± 14.75 mg CE/g RCW, respectively. RCW reduced intracellular reactive oxygen species level and increased the action of antioxidant enzymes, such as catalase, superoxide dismutase, and glutathione peroxidase in tumor necrosis factor-α (TNF-α)/interferon-γ (IFN-γ)-stimulated HaCaT cells. Moreover, mRNA expression of the pro-inflammatory cytokines, including TNF-α, interleukin-1β, and interleukin-6, was downregulated by RCW in the TNF-α/IFN-γ-stimulated cells. The levels of inflammatory chemokines (thymus- and activation-regulated chemokine; eotaxin; macrophage-derived chemokine; regulated on activation, normal T-cell expressed and secreted; and granulocyte-macrophage colony-stimulating factor) and intercellular adhesion molecule-1 were decreased in the TNF-α/IFN-γ-stimulated HaCaT cells after RCW treatment. Additionally, the mRNA expression levels of filaggrin and involucrin, proteins that form the skin, were increased by RCW. Furthermore, RCW inhibited the nuclear factor kappa-light-chain-enhancer of the activated B cells pathway in the TNF-α/IFN-γ-stimulated HaCaT cells. Collectively, the present investigation indicates that RCW is a potent substance that inhibits AD.

Bhandary B, Lee GH, So BO, Kim SY, Kim MG, Kwon JW, Song JY, Lee HK, Kim HR, Chae SW, Chae HJ. Rubus coreanus inhibits oxidized-LDL uptake by macrophages through regulation of JNK activation. Am J Chin Med. 2012;40(5):967-78. doi: 10.1142/S0192415X12500711. 

Abstract.Oxidized low-density lipoprotein (oxLDL) contributes to atherosclerosis in part by being taken up into macrophages via scavenger receptors and leading to foam cell formation. Herbal compounds that have been used to treat blood stasis (a counterpart of atherosclerosis) for centuries include extracts of medicinal plants in the Rosaceae and Leguminosae families. In this study, we investigated the effect of the unripe Rubus coreanus (Korean black raspberry) fruit extract on oxLDL uptake by murine macrophage cells. In the presence of Rubus coreanus extract (RCE), Dil-labeled oxLDL uptake was inhibited in a dose-dependent manner. SP600125, a specific JNK inhibitor, inhibited the uptake of Dil-oxLDL into macrophages. RCE also inhibited JNK phosphorylation in a time- and dose-dependent manner in macrophages treated with oxLDL. These results indicate that among the mitogen-activated protein kinases, JNK phosphorylation is inhibited by RCE, which is likely the mechanism underlying the RCE-induced inhibition of oxLDL uptake by macrophages.

Kim KJ, Jeong ES, Lee KH, Na JR, Park S, Kim JS, Na CS, Kim YR, Kim S. Unripe Rubus coreanus Miquel Extract Containing Ellagic Acid Promotes Lipolysis and Thermogenesis In Vitro and In Vivo. Molecules. 2020 Dec 16;25(24):5954. doi: 10.3390/molecules25245954.

Abstract. Previously, we demonstrated that a 5% ethanol extract of unripe Rubus coreanus (5-uRCK) and ellagic acid has hypocholesterolemic and antiobesity activity, at least partially mediated by the downregulation of adipogenic and lipogenic gene expression in high-fat diet (HFD)-fed animals. The present study investigated the thermogenic and lipolytic antiobesity effects of 5-uRCK and ellagic acid in HFD-induced obese C57BL/6 mice and explored its mechanism of action. Mice fed an HFD received 5-uRCK or ellagic acid as a post-treatment or pretreatment. Both post-treated and pretreated mice showed significant reductions in body weight and adipose tissue mass compared to the HFD-fed mice. The protein levels of lipolysis-associated proteins, such as adipose triglyceride lipase (ATGL), phosphorylated hormone-sensitive lipase (p-HSL), and perilipin1 (PLIN1), were significantly increased in both the 5-uRCK- and ellagic acid-treated mouse epididymal white adipose tissue (eWAT). Additionally, thermogenesis-associated proteins, such as peroxisome proliferator-activated receptor α (PPARα), carnitine palmitoyl transferase-1 (CPT1), uncoupling protein 1 (UCP1), and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), in inguinal white adipose tissue (ingWAT) were clearly increased in both the 5-uRCK- and ellagic acid-treated mice compared to HFD-fed mice. These results suggest that 5-uRCK and ellagic acid are effective for suppressing body weight gain and enhancing the lipid profile.

Lee EJ, Yang JH, Choi JG, Chung HS. Augmented Antitumor Effect of Unripe Rubus coreanus Miquel Combined with Oxaliplatin in a Humanized PD-1/PD-L1 Knock-In Colorectal Cancer Mouse Model. Cells. 2022 Sep 14;11(18):2876. doi: 10.3390/cells11182876.

Abstract. Immune checkpoint inhibitors (ICIs) have been shown to be extraordinarily effective in patients with colorectal cancer (CRC). However, the current ICIs still have adverse effects and limited efficacy of ICI monotherapy. We used a natural product to overcome the vulnerability of ICIs and tried a combination therapy with oxaliplatin to enhance the programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) blockade anticancer effect. In the present study, we evaluated the T cell-mediated antitumor immunity with Unripe Rubus coreanus Miquel extract (RCE), which exerts anticancer properties via PD-1/PD-L1 blockade, combined with oxaliplatin in a co-culture cell model and allograft tumor humanized PD-1 mice. We found that RCE plus oxaliplatin apparently activates hPD-1 tumor-infiltrating CD8+ T cells, resulting in elevations of released interleukin-2 (IL-2) and granzyme B (GrB), and kills hPD-L1 MC38 CRC cells. RCE plus oxaliplatin considerably reduced tumor growth in humanized PD-1/PD-L1-expressing mouse MC38 CRC allograft. Moreover, RCE plus oxaliplatin remarkably increased the infiltration of CD8+ T cells in tumor tissues, as well as increasingly produced GrB of tumor-infiltrating CD8+ T cells in the tumor microenvironment. Our study delineated combination therapy with RCE as a PD-1/PD-L1 blockade and oxaliplatin to improve the response to immune checkpoint blockade therapy in conjunction with standard chemotherapy regimens in CRC.