Changes in vitamin content and sensory characteristics of frozen wild berries during storage

Introduction.The aim of the study was to evaluate changes in the content of ascorbic acid, bioflavonoids, and β-carotene, as well as the organoleptic properties of frozen wild berries under the influence of cryoprotectants after long-term storage.Materials and methods.Wild edible berries (fresh, frozen, and defrosted) of chokeberry, blackberry, raspberry, blueberry, and guelder rose were used in the study.The berries were frozen under the protection of a cryoprotectant (a 10% aqueous solution of sucrose together with a 1% solution of citric acid).Defrosting of frozen berries after 9 months of storage was performed by four different methods to determine the most effective one.Results and discussion.The berries contain ascorbic acid ranging from 49.7 (guelder rose) to 139.5 (chokeberry) mg/100 g of fresh weight (FW), and β-carotene ranging from 1.94 (blueberry) to 3.76 (chokeberry) mg/100 g FW.Wild berries had high content of bioflavonoids, ranging from 785 mg/100 g FW (guelder rose) to 1654 mg/100 g FW (blueberry).Even after 9 months of storage, frozen berries under the protection of cryoprotectants lost no more than 11.6% of ascorbic acid that is the most labile bio-component; sensory characteristics of the berries showed almost no significant difference with fresh raw material by all indicators.The methods of defrosting frozen berries affect sensory characteristics and the indicator of cell juice loss of the resulting product; the most effective method was found to be defrosting berries in a refrigerator at a temperature of 0 °C for 30-33 minutes.This method preserved the tissue strength of the berry surface completely, resulting in null loss of cell juice.The best indicators were obtained after thawing the berries in air at a temperature of 18-22 °C for 130-135 minutes: the loss of cell juice was 19.8%, and the surface of the berries had cracks, so the sensory characteristics were 4.1 points, and 3.7 points for the color.Frozen berries proved to be a reliable source of vitamins for dietary needs: 50 g of berries provide the human body with 24.9-65.7% of the Recommended Dietary Allowances for ascorbic acid, 19.0-36.6% for β-carotene, and 156.4-332.2%for bioflavonoids (priority was given to blueberries).Conclusions.Berries, processed with a water solution of cryoprotectant before freezing, after 9 months of storage, showed almost no significant difference with fresh raw materials in terms of vitamin content and sensory characteristics.The optimal conditions for defrosting of berries was temperature 0 °C for 30-33 minutes.