Blanching benefits antioxidants in processed berries

By Jess Halliday

- Last updated on GMT

A new study has concluded that organically-grown raspberries and blueberries do not have higher levels or activity of antioxidant activity, but phytochemical content can be significantly affected by processing method.

Great debate raged over the perceived nutritional superiority of organic produce last year, after a review of studies funded by UK’s Food Standards Agency (FSA) was published in the American Journal of Clinical Nutrition​. The review concluded that the current science does not indicate that are big differences.

A similar study based on data collected by France’s AFFSA and published in the journal Agronomy for Sustainable Development​, however, concluded that there are nutritional differences.

The researchers for the new study acknowledged some previous research has concluded that organically-grown produce does have enhanced phytochemical content, but they said insufficient attention has been given to possible factors behind this.

One factor they suggest is that because biosynthesis on phenolic compounds, whose presence is correlated with decreased damage from pests, pathogens and UV radiation, play a protective role in the plant. Since they have more cause for action when pesticides are not used, the hypothesis is that organically grown produce is healthier by virtue of higher phenolic compound levels.

The team set out to compare antioxidants in red raspberries (rubus idaeus​, Duch and Meeker cultivars) and highbush blueberries (vaccinium corymbosum​, Duke and Reka cultivars). The berries were harvested from eight commercial farm fields in Washington State, USA, at maturity. Certified organic and conventional fields were paired for crop, location and cultivar.

After analysing the berries’ tissues (prepared by powdering using liquid nitrogen), they found that there was no relation between the production system and total anthocyanins and phenolic compounds and antioxidant activity.

Some differences were seen between the sets of paired fields, however, and the duke blueberries were seen to have higher phytochemical levels than the Reka blueberries. Phytochemical contents of mechanically harvested organic red raspberries did tend to be higher in berries harvested by hand.


The second part of the Washington study involved assessing the impact of processing on berries’ phenolic compounds. The researchers said this is important because berries are recognized as being healthy foods, but they do not grow year-round in the Northern hemisphere. Thermal processing such as canning, juicing and pureeing enables transportation.

After canning, the level of total anthocyanins was seen to decrease by up to 44 per cent. The phenolic contents and the antioxidant activity generally increased for both the raspberries and the blueberries, by up to 50 and 53 per cent respectively.

However the team observed that more phytochemicals were retained when the berries were blanched before pureeing or juicing.

“The higher recovery of phenolic compounds resulted in a significant increase in antioxidant activity of blueberry puree/juice. The addition of a blanching step prior to blueberry processing should be considered important for important for enhancing the health benefits of blueberry purees and juices,”​ they concluded.


Journal of the Science of Food and Agriculture

DOI 10.1002/jsfa.3882

“Effect of thermal treatments on phytochemicals in conventionally and organically grown berries”

Authors: Sablani, S., Andrews, P., Davies, N., Walters, T., Saez, H., Syamaladevi, R., and Mohekar, P.

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