Polyphenol characterization of three varieties of Blackberry fruits (Rubus adenotrichos), cultivated in Costa Rica

BACKGROUND:Blackberries (Rubus spp.) are fruits rich in secondary components (anthocyanins, proanthocyanidins, phenolic acids, carotenoids and others), recognized for their health benefits. OBJECTIVE:To evaluate the content of different types of phenolic compounds and their antioxidant activity in several extracts of three varieties of blackberry fruit (Rubus adenotrichos) (red thorned, thornless and sweet), using different blackberry standards. METHODS:The varieties of blackberry fruit were analyzed in three stages of maturation (green, red and black). The evaluation of the phenolic compounds was carried out by applying commercial standards and own standards to the same samples, following the Folin-Ciocalteu, differential pH, DMAC, and ORAC procedures. RESULTS:The red thorned variety presented the best results with a concentration of polyphenols of 183.0±0.5 mg GAE/g DS, antioxidant capacity of 3322±10 μmol TEAC/g DS, a value of 15.4±0.3 mg of cyanidin-3-glucoside eq/g DS of anthocyanins, and a value of 9.26±0.03 mg 4'-O-methylgallocatechin eq/g DS for of proanthocyanidin content. CONCLUSIONS:Our results show the limitation of a currently used standard, gallic acid and 4'-O-methylgallocatechin, for quantification of total polyphenols and proanthocyanidin respectively, and outline the development and validation of a more robust and accurate standard for blackberry fruit analysis.