Background and methodology:
This study examined the levels of anthocyanin in the skin of Syrah grapes. Anthocyanin is responsible for the red, purple and blue colors of many fruits, vegetables, grains and flowers, and also of interest for possible health benefits as antioxidants.
The grapes were harvested at different stages of ripening from production systems using either organic or conventional systems. Samples of grapes were collected in each plot from the veraison stage (the moment they began to change color) to full maturity. Using high-performance liquid chromatography, researchers measured the total amount of 9 different anthocyanins.
Findings:
The total content of anthocyanins in conventionally grown grapes was significantly higher compared to that found in grapes grown organically. The accumulation of anthocyanins reached a maximum 28 days after veraison (also the period of highest temperature), which then decreased until harvest.
In all samples, grapes from conventional plots had higher proportions of delphinidin, petunidin, malvidin, and acylated malvidin glucosides compared to grapes from organic plots. For each grape variety considered, climatic conditions and agronomic practices were important factors. Researchers said the higher levels of stress during the dry and hot summer of 2002 probably resulted in the higher leves of anthocyanin in the conventionally grown grapes as a result of the higher biotic stress from application of synthetic chemicals in those plots.
Reference:
Vian, M. A., Tomao, V., Coulomb, P. O., Lacombe, J. M., & Dangles, O. (2006). Comparison of the anthocyanin composition during ripening of syrah grapes grown using organic or conventional agricultural practices. Journal of Agricultural and Food Chemistry, 54(15), 5230-5235. Available on-line at: http://pubs.acs.org/doi/full/10.1021/jf0531609