Studies have shown that many factors can significantly affect the concentrations of each of these important compounds in berries. As noted, ripening can have a significant effect.

Some of the compounds in berries are sensitive to heat and if heated during processing will lose a great deal of their medicinal value.

For example, processing blueberries into a juice reduces the ellagic acid 70 to 82 percent, and anthocyanins around 67 percent. Blackberries also lose a significant amount of their beneficial compounds with storage and processing.

But sometimes processing can actually improve the concentration of various compounds.

For instance, blanching (heating to 85 degrees for 3 minutes) increases the content of anthocyanins in blueberries, and freezing blueberries increases their antioxidant capacity for three months.

Freezing cranberries can increase their phenolic content four times higher than with juicing.

Also important are plant breeding and variety, growing locations, fertilizers used, growing season, pH, temperature, and site (greenhouse, open-field, plastic tunnel, hydroponics).

Based on these factors, the contents of useful compounds can vary by as much as 25-fold.

Compost has been found to be the best fertilizer to use, as it increases these medicinal compounds.