How Does Freezing Affect Polyphenols in Fruits and Vegetables?

October 12, 2025 •

4 min read

Studies on haskap berries showed a significant reduction in phenolic compounds after six months of frozen storage at -18°C, raising questions: does freezing affect polyphenols and if so, to what extent? The answer is complex, with impacts varying based on the food type, preparation methods, and storage duration.

Quick Summary

The impact of freezing on polyphenol content is nuanced, with initial freezing often preserving compounds effectively. However, long-term frozen storage and improper thawing can lead to gradual degradation. Pre-freezing treatments like blanching and the physical state of the food (whole vs. puree) are critical factors influencing nutrient retention.

Key Points

Polyphenol retention is high with flash-freezing: Produce frozen quickly after harvest, at peak ripeness, retains a nutritional profile comparable to fresh food.
Long-term storage can cause gradual losses: Studies show that extended storage in a freezer, even at stable temperatures, can lead to a gradual decrease in total polyphenol content over months.
Blanching is a crucial pre-treatment: For vegetables, a quick blanching period before freezing deactivates enzymes that would otherwise degrade polyphenols during storage.
Cell structure and food form matter: Whole, intact foods tend to retain polyphenols better than purees or juices, where cell disruption can accelerate oxidation.
Thawing methods influence nutrient loss: Significant polyphenol loss can occur during thawing due to damaged cell walls leaking nutrient-rich drip, a process minimized by slow thawing.
Freezer temperature and air exposure are critical: Maintaining a consistent temperature of 0°F or lower and using airtight packaging helps prevent nutrient degradation caused by fluctuating temperatures and oxygen.

Understanding the Impact of Freezing on Polyphenol Stability

Polyphenols are a group of beneficial plant compounds and antioxidants found in many fruits and vegetables. Their stability during food processing, including freezing, is a key concern for maintaining nutritional quality. While freezing is widely considered an excellent method for long-term food preservation, it's not without its effects on these sensitive compounds. The influence of freezing depends on several factors, from the food's cellular structure to the specific conditions of storage.

The Immediate Effects of Freezing

The act of freezing itself does not destroy nutrients, including polyphenols. In fact, produce that is flash-frozen shortly after harvest often retains high levels of nutrients because it is captured at its peak ripeness, when polyphenol concentrations are at their highest. In contrast, fresh produce can lose a significant portion of its vitamins and antioxidants during transport and extended shelf life. However, the process of forming ice crystals can damage the cell walls of plant tissue. This cellular rupture can lead to a release of enzymes, like polyphenol oxidase (PPO), which can accelerate the degradation of polyphenols and other compounds once the food is thawed. This is why frozen food can become mushy upon thawing.

The Role of Frozen Storage and Temperature

Long-term frozen storage is a major factor influencing polyphenol stability. Research shows that while initial freezing is effective, gradual degradation can occur over time, even at stable freezer temperatures. For instance, a study on haskap berries found that after six months at -18°C, the total phenolic content was reduced by 37–47%. A different study on peach pulp found that antioxidant capacity and total phenolic content changed by less than 20% after 360 days of frozen storage. The storage temperature can also play a role, though results vary by study and food type. Some studies suggest that lower temperatures, such as -30°C, can help better preserve antioxidants compared to -20°C, while others show little significant difference.

How Pre-Treatments Impact Retention

To minimize nutrient loss and enzymatic activity, food processors often use pre-freezing treatments. Blanching, which involves a brief exposure to hot water or steam followed by rapid cooling, is a common technique for vegetables. It effectively deactivates enzymes like PPO that cause spoilage and nutrient degradation.

Benefits and drawbacks of blanching:

Prevents Degradation: By deactivating oxidative enzymes, blanching significantly improves the retention of phenolic compounds during subsequent freezing and storage.
Minimizes Leaching: Steam blanching is often preferred over water blanching, as it minimizes the leaching of water-soluble compounds like polyphenols into the water.
Vitamin Loss: A downside is that blanching can cause some loss of heat-sensitive, water-soluble vitamins, though this is often considered a minimal trade-off for overall quality and nutritional retention compared to not blanching.

Another approach for fruits is the addition of an acidic solution, like ascorbic acid, to inhibit enzymatic browning and vitamin C loss. This is especially useful for fruits that can suffer significant color and nutrient loss upon thawing.

The Crucial Impact of Thawing

Thawing is another critical stage where nutrient loss can occur. As the frozen food thaws, the damaged cell walls can lead to the loss of cell contents, including water-soluble polyphenols, through drip. The thawing rate also matters, with slow, controlled thawing often resulting in better moisture retention and less damage than rapid thawing. For instance, thawing frozen berries can result in a significant loss of juice and a corresponding reduction in total polyphenol content if not managed correctly. Thawing at refrigerator temperatures is generally recommended to minimize enzymatic reactions and liquid loss.

Does Freezing Affect Polyphenols: A Comparative Look


Feature	Effect of Freezing on Polyphenols	Key Contributing Factors
Initial Freezing	High retention, similar to fresh, especially with flash-freezing.	Quality of produce at harvest, speed of freezing.
Frozen Storage	Gradual degradation over time, with losses accumulating, especially after a few months.	Storage duration, fluctuating temperatures, oxygen exposure.
Food Form (Whole vs. Puree)	Whole foods retain more polyphenols due to intact cell structure.	Cell disruption in purees or juices promotes enzymatic oxidation.
Pre-Treatment	Blanching for vegetables inactivates enzymes, greatly improving retention.	Method (steam vs. water), duration of blanching.
Thawing Process	Can lead to significant polyphenol loss as compounds leach out in drip.	Thawing method and speed, cell wall damage from ice crystals.

The Takeaway

The question of whether freezing affects polyphenols has no simple 'yes' or 'no' answer. It depends heavily on how the food is processed, stored, and prepared. For many people, frozen fruits and vegetables offer a nutritionally comparable and often more convenient and affordable option than fresh produce, which can lose nutrients during transit and storage. The key to maximizing polyphenol retention is to use high-quality, pre-blanched frozen products and minimize the time and temperature fluctuations during frozen storage and thawing. For more in-depth research on food processing and nutrients, the National Institutes of Health provides a comprehensive overview: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8156030/.

Conclusion

Ultimately, freezing is a very effective method for preserving the nutritional value of plant foods. While some polyphenol degradation is inevitable over extended periods of frozen storage, many commercially frozen fruits and vegetables are processed at their peak ripeness, locking in nutrients that might otherwise be lost. For home freezing, utilizing proper pre-treatments like blanching for vegetables can make a significant difference. By understanding the factors involved, from the speed of freezing to the method of thawing, consumers can make informed choices to retain the maximum health benefits from their frozen produce.

Frequently Asked Questions

Not necessarily. Frozen fruits are often picked at peak ripeness and flash-frozen, locking in nutrients. Fresh fruit, in contrast, may lose nutrients during long-distance transportation and storage. The nutrient difference is often minimal.

Blanching can cause some loss of water-soluble polyphenols, but it is a necessary step for many vegetables. It deactivates enzymes that cause significant nutrient loss during freezing and storage, ultimately preserving more of the nutritional value overall.

To minimize polyphenol loss from berries, thaw them slowly in the refrigerator instead of at room temperature or in the microwave. This reduces the amount of drip loss and the resulting leaching of water-soluble compounds.

The act of freezing itself does not directly damage the antioxidant properties, but the process of freezing and storage can lead to degradation over time due to enzymatic activity and oxidation. Properly managed freezing and thawing minimizes this.

Yes, purees and juices have a more disrupted cell structure than whole foods. This allows more oxygen exposure to enzymes and substrates, which can accelerate the degradation of polyphenols during freezing and storage.

Yes, in some cases, freezing can cause cell wall damage that releases bound phenolic compounds, potentially making them more accessible and increasing the measured polyphenol content. This effect is seen in some specific studies, though results vary.

While produce is generally safe to eat for long periods, most significant polyphenol degradation occurs within the first few months of storage. For optimal nutrient retention, it is best to consume frozen produce within a year.