Relative Proportions of Individual Blueberry Anthocyanins Vacillate Within and Between Growing Seasons

Abstract

Blueberries accumulate up to 18 different types of anthocyanins unlike most other berries, such as blackberries and blackcurrant that tpically contain only 5–8, with different genotypes varying in their anthocyanin profile. Individual anthocyanin moietes vary in health‐relevant biological activity due to differences in their chemical structures, absorption, and metabolism in the gut. Variation in total anthocyanin content between growing seasons has been previously documented, but our study is the first in which inter‐ and intra‐seasonal fluctuations of individual blueberry anthocyanins across genotypes has been examined. The anthocyanin profiles of six blueberry genotypes were assessed weekly over two growing seasons by analyzing anthocyanin extracts of ripe berries by HPLC. While individual genotypes differed in total and relative anthocyanin content, all experienced similar trends across each season. Total anthocyanin content ranged between 10–28 mg per gram fresh weight and, despite some fluctuation, increased as the season progressed for all genotypes, even though only berries at peak ripeness were harvested at any time point. Relative levels of malvidin and delphinidin glycosides displayed fluctuations between 3–20% of total anthocyanin content over the course of either picking season for each genotype, and interestingly, were inversely proportional throughout the season. This shift was most pronounced in the Legacy variety, where delphinidin levels increased by 15% and malvidin decreased by 16% over the course of the growing season in 2014. The opposite trend was observed in 2015, with delphinidin decreasing 10% and malvidin increasing 10% across the season. Delphinidin and malvidin are in the same biosynthetic pathway, separated only by 2 methylation steps. While these two were observed to be inversely propotional, the single‐methylated intermediate, petunidin, remains relatively constant across the season for all varieties with a maximum of 2% change for the Legacy variety. These results suggest that an increase in expression in the methylation biosynthetic step involving O‐dihydroxyphenol O‐methyltransferase from delphinidin favors an increase in the two‐step methylation to malvidin over the single methylation to petunidin. Given the many health benefits of blueberries and specifically anthocyanins, the flux in specific anthocyanin concentrations over multiple seasons is of interest in order to determine not only peak concentrations of anthocyanins present, but also the most favorable anthocyanin profile for specific interventions in human health and metabolism.