Drying Berry Press Residues: What Happens to Anthocyanins and Polyphenols?

Berry press residues - the skins, seeds, and pulp left after juice production - are often treated as waste, despite being rich in anthocyanins and other polyphenols with antioxidant properties. Their potential use as functional food ingredients or natural colourants depends largely on how well these compounds survive processing, particularly drying, which is necessary for stabilisation and storage.

A recent study by Gricenko et al. (2026), published in Frontiers in Sustainable Food Systems (https://doi.org/10.3389/fsufs.2025.1733151), provides a systematic comparison of how different drying methods and temperatures affect anthocyanin stability, polyphenolic content, and antioxidant activity in press residues from ten commonly processed berry species.

Why drying matters?

Drying is a critical step in the valorisation of berry by-products. While it extends shelf life and reduces microbial risk, it can also promote thermal and oxidative degradation of sensitive compounds. Previous studies have examined individual drying methods or single berry species, but comparative data across multiple berries and drying conditions have been limited. This study addresses that gap by applying identical drying protocols to all samples.

Experimental approach

Press residues from ten berry species - including chokeberry, bilberry, blueberry, honeysuckle berry, blackcurrant, cranberry, raspberry, and strawberry were dried using three methods:

• Freeze drying (as a low-degradation reference),

• Conventional hot-air drying at 30–90 °C,

• Vacuum drying at 30–90 °C under reduced oxygen conditions.

The authors measured total polyphenolic content (TPC), total anthocyanin content (TAC), antioxidant activity (DPPH assay), and the profiles of 24 individual anthocyanins using UPLC–MS/MS.

Key findings

Freeze drying preserved bioactive compounds most effectively. Across all berry species, freeze drying resulted in the highest retention of both polyphenols and anthocyanins, confirming its status as the least degradative method. However, it is also energy-intensive and costly, limiting its industrial scalability.

Vacuum drying performed well at moderate temperatures. At 30–60 °C, vacuum drying preserved TPC and TAC at levels comparable to freeze drying and consistently outperformed conventional drying. The reduced oxygen environment slowed oxidative degradation, particularly for anthocyanins.

A degradation threshold was observed above ~75 °C. For both vacuum and conventional drying, sharp losses in polyphenols and anthocyanins occurred at 90 °C. Oxygen exclusion alone was insufficient to prevent degradation once thermal stress exceeded this threshold.

Berry species responded differently. Chokeberry and honeysuckle berry, despite having the highest initial anthocyanin and polyphenol contents, were among the most sensitive to high temperatures. Raspberry, strawberry, and cranberry residues showed comparatively greater thermal stability, especially under vacuum drying. These differences highlight the importance of matrix effects and species-specific optimisation.

Anthocyanin structure influenced stability. Not all anthocyanins degraded equally. Rutinoside and simple glucoside derivatives were relatively stable, typically showing losses below 30%, whereas sambubioside and diglucoside forms often degraded by more than 50%. This structure–stability relationship provides mechanistic insight that goes beyond total anthocyanin measurements.

Antioxidant activity correlated more strongly with total polyphenols than anthocyanins. While anthocyanins contributed to antioxidant capacity, total polyphenolic content showed the strongest correlation with DPPH radical scavenging activity. This suggests that maintaining overall phenolic integrity may be more important than preserving anthocyanins alone, depending on the intended application.

Implications for food systems and by-product valorisation

The results indicate that vacuum drying at moderate temperatures offers a practical compromise between compound preservation and industrial feasibility. It can substantially reduce energy costs compared to freeze drying while maintaining much of the nutritional and functional value of berry press residues.

From a sustainability perspective, these findings support the use of berry by-products as sources of functional ingredients, natural colourants, or antioxidant-rich extracts provided that drying conditions are carefully optimised. Importantly, the study shows that “one-size-fits-all” processing strategies are unlikely to be effective across different berry species or target compounds.

Concluding remarks

This work provides one of the most comprehensive cross-species evaluations of anthocyanin and polyphenol stability during drying to date. By linking drying conditions, berry matrix effects, and anthocyanin structure, it offers practical guidance for designing processing protocols that balance product quality, energy use, and economic viability. As interest in food waste valorisation continues to grow, such data-driven optimisation will be essential for translating laboratory findings into scalable applications.