Freeze-drying strawberries keeps all their Vitamin C and polyphenols and 92% of their antioxidants, saving more nutrients than by chilling which can lose over 80% of antioxidant concentrations.
It is well known that heat destroys most of the antioxidant potential of berries, making canned and juicing that involve friction and heat a poor choice to maximize their antioxidant potential.
The same is true for refrigeration. It appears that whenever fruit experiences temperature variants from its original state, antioxidant potential is affected, that is unless it is freeze dried.
Researchers at Sheffield Hallam University, UK measured Vitamin C, total antioxidant capacity (TAC), and total phenolic content (TPC) in fresh, chilled and freeze-dried strawberries.
Freeze-drying had no significant impact on nutrient content, but refrigerated fruit experienced large losses.
Researchers at the Ohio State University Comprehensive Cancer Center examined the effect of freeze-dried black raspberries on genes altered by a chemical carcinogen in an animal model of esophageal cancer.
The carcinogen affected the activity of some 2,200 genes in the animals’ esophagus in only one week, but 460 of those genes were restored to normal activity in animals that consumed freeze-dried black raspberry powder as part of their diet during the exposure.
“Freeze drying the berries concentrates these elements about ten times, giving us a power pack of chemoprevention agents that can influence the different signaling pathways that are deregulated in cancer,” said principal investigator Gary D. Stoner, a professor of pathology, human nutrition and medicine who studies dietary agents for the prevention of esophageal cancer.
Packaging Research Planned
John McAughtrie, technical director, Chaucer Foods, said the research highlights the nutritional benefits of freeze-drying fruit and vegetables.
“We are now planning to undertake further studies to compare the nutrient retention of freeze dried fruit and vegetables against those that have been dried using alternative technologies, and to consider the effects of packaging and storage on nutrient retention.”
In the fruit chilled for seven days, TPC was reduced by 82% from fresh, Vitamin C was down by 19%, and 23% of TAC was lost. These are similar losses experienced through friction and heating mechanisms while juicing.
TPC is a measure of polyphenols, chemicals with antioxidant health benefits found in fruits, vegetables, tea and wine. The largest group of polyphenols is flavonoids, which can contribute to food’s color and mouthfeel.