Differences in phenolic content and antioxidant activity of berries


Significant differences in phenolic content and antioxidant activity among different parts of berry fruits were reported. Therefore, correlations among phenolics, antioxidant activities, and scavenging capacities vary with different tissues. In cranberries, outer pericarp tissue contained a higher concentration of ellagic acid compared to pulp and seeds.

In blackberries, differences in ellagic acid were also observed between pulp and seeds. Strawberry achenes, on average, contributed to 50% of total phenolics, 43% of total flavonoids, and 37% of total anthocyanin content of the whole fruit. The achenes should be taken into account as important phenolic contributors for strawberries.

Phenolic content as well as antioxidant activity in strawberries were higher in achenes than in thalamus. The achenes contributed about 14% of the antioxidant activity in strawberries in spite of comprising only 1% fresh weight of the total fruit, and the main contribution was from ellagic acid and its derivatives. Meanwhile, resveratrol was also found to be higher in achenes than in thalamus. In both the achenes and thalamus of strawberries, total phenolic content, and total flavonoid content were correlated to DPPH activity.

There is evidence that flavonoid biosynthesis is tightly associated with the developmental stage of fruits. In all berry fruits, anthocyanin content increases as the berries mature. For example, in cranberries, increases in levels of flavonols and anthocyanins during fruit ripening were observed. In blackberries and strawberries, total phenolic content significantly decreased as the fruit matured from the green to ripe stages. Interestingly, in raspberries, total phenolic content decreased from the green to pink stages followed by a significant increase from the pink stage to the ripe stages.

Antioxidant capacity varies considerably with different levels of maturity. In blueberries, increased maturity at harvest increased ORAC and anthocyanins. The antioxidant capacity of blueberry fruits at five stages of maturation and ripening was studied and it was found that antioxidant activity was strongly related to the total phenolic content in all stages. Antioxidant activity was higher at early maturation and during initial pigmentation than at full ripeness.

This may be attributed to the higher concentrations of hydroxycinnamic acids and flavonols before ripening, whereas lower antioxidant activity of horticulturally mature berries may suggest that anthocyanins have less antioxidant potential than other phenolic compounds such as flavonols.

Anthocyanins of all varieties of blueberry increased during successive harvest stages. Meanwhile, flavonols and hydroxycinnamic acids decreased from the unripe green to ripe blue stage of berry ripening. Blueberry antioxidant activity, as well as total phenolic content tended to decrease during ripening. Lingonberries have a high content of antioxidants, and significant differences were found in antioxidant activity, total anthocyanin, and total phenolic contents among different maturities of lingonberry.

Lingonberry fruit harvested during their green stage consistently yielded the highest ORAC values, DPPH radical scavenging activity, and total phenolic contents, followed by the pink stage fruit, and finally, the red fruit. This may be due to abundant procyanidin contents in the green fruit. There was a positive correlation between total phenolic contents and free radical scavenging activity in lingonberries. In blackberries, the total anthocyanin content increased considerably during ripening, while total phenolic content and antioxidant properties did not show such pronounced changes.

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