US researchers observed that while the half-life of anthocyanins in bilberry extracts is less than eight minutes when subjected to cooking temperatures above 125ºc, anthocyanin activity could be increased between 100 and 125ºc.
“The results of this study suggest that the antioxidant activity in bilberry extract could be increased by heating between 100 and 125ºc, at a short period of time,” wrote the researchers in the Journal of Food Science.
“The free radical scavenging capability of the heated bilberry extract at 125ºc for 30 min, 100ºc for 10 or 20 min, or 125ºc for 10 min was significantly higher than the original bilberry extract.”
However they noted anthocyanin stability was compromised at temperatures over 100ºc.
“The information of this study could be helpful in utilizing natural anthocyanin extract as a food supplement or colorant for high-temperature extruded or baked foods to maximally maintain anthocyanins and antioxidant activity during processing,” the researchers concluded.
Ten anthocyanins in a bilberry extract were tested for and degradation rates followed “1st-order reaction kinetics” at temperatures of 80, 100, 125 and 150ºC.
“All anthocyanins in the bilberry extract were totally degraded to undetectable level in 10 min at heating temperature of 150ºc,” the researchers from the Department of Food Science at the Louisiana State University Agricultural Center in Baton Rouge wrote.
“Though the degradation rate constants of anthocyanins were not significantly different from each other at the same heating temperature, they increased drastically when heating temperature was increased to 125ºc,” the researchers found.
“These results support that anthocyanins are extremely vulnerable at temperatures over 100ºc,” they added.
Anthocyanins are responsible for the bright red, purple and blue colours of some fruits, including the bilberry. Anthocyanins function as antioxidants in the body and have therefore gained attention for their health-giving potential.
The bilberry has been grouped with other fruits such as the cranberry, the blueberry, acai and the goji berry and called superfruits because of their boosted antioxidant levels.
Their incorporation in the form of extracts into foods, beverages and food supplements, not to mention cosmetics products, is becoming more common as companies look for novel – and natural – ways to enhance the nutritional profile of their products.
The researchers noted that there had been little study into the effect of dry baking and extrusion on anthocyanin levels.
Previous studies had shown the anthocyanin degradation that occurred with the processing and storage of fresh fruits and vegetables.
The 10 anthocyanins tested for were delphinidin galactoside, delphinidin glucoside, cyanidin galactoside, delphinidin arabinoside, cyanidin glucoside, cyanidin arabinoside, petunidin glucoside, malvidin galactoside, peonidin glucoside and malvidin arabinoside.
Journal of Food Science
“Changes of Anthocyanins, Anthocyanidins, and Antioxidant Activity in Bilberry Extract during Dry Heating”
Vol. 73, Number 6, 2008