Introduction of Black Raspberry
The binomial name of black raspberry is Rubus occidentalis, which is belongs to the species of Rubus native to eastern North America. Other names occasionally used include black cap raspberry, black caps, scotch cap, and thimbleberry. Black raspberry is a deciduous shrub with prickly shoots, growing to 2-3 m tall. In the first year, stems are strong-growing with three leaflets on the leaves on flowering branchlets. The flowers have long, slender sepals which is more than twice as long as the petals. The fruit is round-shaped with diameter aggregation of drupelets. The fruit is edible and has high content of ellagic acid and anthocyanins.
Because the black raspberry is rich in anthocyanin pigments, it usually have very dark purple black fruits. Sometimes, the gene mutations in controlling anthocyanin production can result in yellow-fruited variants. The black raspberry is also closely related to the red raspberries, sharing the distinctively white underside of the leaves and fruit that readily detaches from the carpel, but differing in the ripe fruit being black, and in the stems being more prickly. The black fruit makes them look like blackberries, though this is only superficial, with the taste being unique and not like either the red raspberry or the blackberry.
Black Raspberry in Cancer Treatment
Over the past decades of years, a numerous evidence have shown that black raspberry is an inhibitor of cancer or premalignancy in high risk human cohorts which is worth further studying. First, mounting epidemiological evidence shows increased consumption of plant based diets is associated with decreased cancer risk, particularly cancers of the aerodigestive tract. Second, strong preclinical results in animal models report that BRB inhibit cancers of the oral cavity, esophagus, colon, breast and skin through targeting processes of proliferation, inflammation, angiogenesis and apoptosis. Third, from a composition stand point black raspberries are rich in vitamins, minerals, fiber, anthocyanins, total phenolics and other bioactive components with cancer inhibitory capacity as previously reviewed. Lastly, initial research reported that maximum concentrations of the major anthocyanins and ellagic acid occurred at 1 to 2 hours in the plasma and between 30 minutes and 4 hours in the urine following BRB consumption with less than 1% overall uptake of the parent or precursor anthocyanins raising concerns regarding bioavailability; however, more recent research shows bioavailability of anthocyanins is comparable to other flavonoid subclasses with significant uptake of diverse metabolites with half-lives ranging from 2 to 96 hours. In turn, the metabolites reportedly modify cellular adhesion and inflammatory signaling cascades, both important cancer associated processes.
Plant Extracts and Cancer Protection
Evidence between single food sources and cancer protection is limited and challenging to study. To date, the strongest cancer inhibitory evidence exists for food groups and especially plant based diets rich in fruits, vegetables and fiber. In terms of extracts, much of the evidence for cancer protection is strongest the closer the extract mimics the whole plant components. 5% BRB, the anthocyanin fraction and ethanol extract which all contained similar levels of anthocyanins were equally effective in inhibiting NMBA-induced esophageal cancer supporting the historical rationale that anthocyanins are the cancer inhibitory component of BRB. However, the BRB derived insoluble or residue fraction was nearly as inhibitor and this fraction contains very low levels of anthocyanins illustrating the complex nature of individual food products and the fact that many foods of interest are not fully characterized from a cancer inhibitory standpoint.
A clinical investigation evaluating red and yellow tomatoes versus similar levels of lycopene in the form of a purified extract reported short term tomato intake induces serum changes that favorably modulate cancer-related gene expression profiles in treated cell lines, including the yellow or lycopene-free tomato; whereas, purified lycopene had both positive and potentially deleterious effects as evidenced by up-regulation of pro-cancer genes. Thus, identification of the main or sole component from a fruit or food matrix responsible for cancer inhibition remains challenging despite technological advancements.
Kresty L A, Mallery S R, Stoner G D. Black raspberries in cancer clinical trials: Past, present and future [J]. Journal of Berry Research, 2016, 6(2):251-261.