Ellagitannin content in raspberry and blackberry cultivars grown in Trentino (Italy)

Berries are amongst the richest sources of phenolic compounds in the human diet. Red raspberries and blackberries contain ellagitannins which are the main class of phenolic compounds. In view of increasing consumer interest in nutrition, the antioxidant content of berries and, in particular, their phenolic profile ought to be promoted as an important trait for breeding programmes. Therefore, screening programmes should be established which clarify qualitative and quantitative genotypic differences in relation to berry antioxidant composition. This study provides a picture of the variability of the ellagitannins in 37 important Rubus genotypes: 21 raspberry and 15 blackberry cultivars. The cultivars investigated were chosen in order to have a balanced number of primocanes and floricanes of different origin and commercial importance. Acid hydrolysis of the ellagitannins in methanol was used to quantify all the major reaction products (ellagic acid, methyl-sanguisorboate, methyl-gallate and an unknown ellagic acid derivate) and estimate their degree of polymerisation. The ratio between maximal and minimal ellagitannin concentrations recorded among red raspberry cultivars did not exceed 1.7; indicating relatively limited variability among the cultivars investigated, while this variability was much higher in blackberries reaching a ratio of 4.4 between the cultivars. The mean degree of polymerisation was between 1.61-1.86 in raspberries and between 1.59 and 1.92 in blackberries, confirming the presence of a mixture of monomers and low oligomers in Rubus ellagitannins. These data support the hypothesis of a genetic determinant of ellagitannins content and profile in the different genotypes.