Postharvest Evaluations of Blackcurrant Fruits with Chitosan and Ultraviolet A (UVA) Treatments

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Summary 

Fresh blackcurrants (Ribes nigrum L.) are usually processed due to their strong pine-like flavor, but the fresh berries may appeal to niche markets and can be marketed as a superfood. This study examined postharvest treatments—chitosan, UV-A, and their combination—on berries stored under refrigeration for 15 days. All berries maintained good visual quality, but UV-A treatments caused increased weight loss and softening without improving microbial control. Chitosan slightly reduced weight loss and effectively suppressed microbial growth. Antioxidant levels were largely unaffected by treatments, with most changes due to storage time. The UV-A + chitosan treatment enhanced some bioactive compounds (likely a consequence of accelerated berry dehydration under UV-A) but offered no added benefit over chitosan alone. Overall, cold storage alone appears sufficient for maintaining the quality of fresh blackcurrants, and the application of chitosan, UV-A, or their combination does not offer significant benefit to justify the investment. 

Introduction 

Blackcurrants are gaining global attention for their health benefits and market potential. They’re rich in vitamin C and powerful antioxidants called anthocyanins, which give the berries their deep purple color and are used in juices, jams, syrups, and more. As consumer demand grows, so does interest in preserving blackcurrant quality after harvest. 

While some research has explored how storage conditions affect blackcurrants, there’s still limited information on how to keep them fresh longer. Chitosan—a natural, edible substance made from shellfish or fungi—has shown promise in protecting fruits by forming a thin coating that reduces spoilage and helps retain nutrients. UV light, especially UV-A (315–400 nm), is another tool that may help reduce microbes and improve fruit quality, though it’s been studied less than other types of UV. 

This study is the first to test both chitosan and UV-A light—separately and together—on blackcurrants after harvest. The goal was to see how these treatments affect berry freshness, weight, firmness, and nutritional quality during storage. 

Methods 

To apply the chitosan coating, a commercial 1% chitosan solution (chitosan, water, acetic acid) was mixed with a 0.3% solution of (w/v) glycerol: water, then stirred thoroughly and kept chilled. Fresh blackcurrants were dipped in the solution for one minute and left to air dry for about three hours. Control berries followed the same process as the chitosan-only group but were dipped in deionized water instead.  

Treated and control blackcurrants were stored in commercial plastic clamshell containers in a walk-in cooler set to 0°C-4°C with 85-90% humidity for 15 days. Each container held about 70 grams of blackcurrants. 

For the combined treatment chitosan-UVA treatment, berries were coated with the chitosan solution, spread onto trays in a single layer, and then exposed to UV-A light throughout the cold storage duration of the study.

Findings

Figure 3. Microbial population measurements on blackcurrants over 15 days of storage. Chitosan and Chitosan + UVA treatments significantly reduced yeast and mold growth compared to the control and UVA-only treatments. Although microbial counts increased over time for all groups, berries treated with chitosan (with or without UVA) had much lower levels even by day 15 than the control and UVA treated berries on day 0.

Antioxidant Activity 

• No significant differences in total antioxidant activity were found among treatments. 

• Flavonoids and anthocyanins significantly increased with time in storage whereas polyphenols remained more stable. 

• UV-A + chitosan significantly enhanced cyanidin-3-galactoside, a beneficial anthocyanin with known health properties. 

• Chitosan immediately decreased luteolin, quercetin, pelargonidin, and peonidin, although only luteolin remained significantly lower than the control on day 15. 

Conclusions 

• Chitosan can help to preserve berry quality in storage by slightly reducing weight loss and controlling microbial growth. 
• UV-A treatment alone tends to accelerate deterioration (weight loss and softening) and is ineffective in microbial control. 
• Antioxidant assays showed that treatments had little effect on total antioxidant levels or activity; most changes were due to storage time. 
• The UV-A + chitosan combination enhanced some bioactive compounds like cyanidin-3-galactoside but did not reduce weight loss or microbial activity beyond chitosan alone.
• Since visual berry quality was similar across treatments and control after two weeks in cold storage, it seems that cold storage alone is effective for extending shelf-life in fresh blackcurrants.