Effects of Air and Freeze Drying on Phytochemical Content of Conventional and Organic Berries

Abstract

U.S. sales of organic products continue to climb due to consumer perception of both environmental and health benefits of organic produce. The objectives of this study were to evaluate the effects of air and freeze drying and blanching treatment prior to air drying on phytochemical content of conventional and organic red raspberries and blueberries. Total anthocyanins and phenolics contents and total antioxidant activity were determined in two cultivars of blueberry (‘Duke’ and ‘Reka’) and in ‘Meeker’ red raspberry harvested under two different techniques (hand and machine). The phytochemical content was determined after subjecting the berries to air and freeze drying with or without blanching pretreatment.

In general, no consistent differences were noted between the phytochemical concentrations in fresh conventional and organic berries. The effect of drying on the retention of phytochemicals depended on drying technique, cultivar, and production system (conventional or organic). Blanching prior to air drying significantly increased the effective moisture diffusivity in both berries, thus reducing the drying time. In general, air drying caused significant reductions in anthocyanins, phenolics, and antioxidant activity in both blueberries and raspberries. Compared to air drying, freeze drying improved retention of phytochemicals during processing and in some cases it even increased the concentration of phytochemicals. The application of blanching resulted in enhanced moisture transport, thus reducing the drying time. The blanching treatment prior to air drying increased the retention of phytochemicals in dried berries.

Keywords:

• Anthocyanin
• Antioxidant activity
• Blanching
• Blueberries
• Effective moisture diffusivity
• Phenolics
• Red raspberries

ACKNOWLEDGMENTS

This research was funded with a Biological and Organic Agriculture (BIOAg) program grant from the Center for Sustaining Agriculture and Natural Resources at Washington State University. The technical assistance of Roopesh Syamaladevi, Pallavi Mohekar, Margaret Collier, John Nguyen, and Dr. Karina Villa-Vega is acknowledged.

Notes

^a Anthocyanin and phenolics are presented on a dry weight (DW) basis. Values in brackets are standard deviation of three replicates.

^b Cyanidin-3-sophoroside-5-glucoside at 524 nm for raspberries.

^c Cyanidin-3-glucoside at 530 nm for blueberries.

Statistical significance between CON and ORG in each crop pair: *p < 0.05, **p < 0.01, ***p < 0.001).

^a The anthocyanin and phenolics are presented on a dry weight (DW) basis. Fresh berries (F) were analyzed after 1 day of storage at refrigeration temperature. Values in brackets are standard deviation of three replicates. Treatments with the same letter in the same column for each crop with the same field code are not significantly different (p > 0.05).

^b Cyanidin-3-sophoroside-5-glucoside at 524 nm for raspberries.

^c Cyanidin-3-glucoside at 530 nm for blueberries.

^a The anthocyanin and phenolics are presented on a dry weight (DW) basis. Fresh berries (F) were analyzed after 1 day of storage at refrigeration temperature. The values in brackets are standard deviation of three replicates. Treatments with the same letter in the same column for each crop with the same field code are not significantly different (P > 0.05).

^b Cyanidin-3-sophoroside-5-glucoside at 524 nm for raspberries.

^c Cyanidin-3-glucoside at 530 nm for blueberries.

NA = not available.