Study on the Effect of Intermittent UV-C Irradiation on Fruit Preservation

Abstract

This study systematically investigated the mechanisms underlying the effects of UV-C LED irradiation on the preservation of fresh fruits. High-power 270–280 nm gallium nitride (GaN)-based UV-C LED chips were employed, with device performance enhanced through optimized heat dissipation structures and a matrix arrangement design. Experimental results demonstrated that, under ambient conditions (22–27°C), a 75% duty cycle UV-C irradiation (45 s on/15 s off) achieved the most effective suppression of mold growth on apple slices and raspberries, completely inhibiting mold proliferation. The 25% duty cycle (15 s on/45 s off) provided a better balance between antibacterial efficacy and maintaining fruit freshness. In a 4°C refrigerated environment, the 25% irradiation mode (15 s on/45 s off, 40 cm distance) reduced the spoilage rate of raspberries from 100% to 20%. For strawberries, while UV-C irradiation completely suppressed mold growth, it induced significant oxidative damage (44.4% of fruits exhibited water-soaked spots) and a higher weight loss rate (14% compared to 6% in the control group). These findings confirm that UV-C irradiation effectively controls postharvest microbial spoilage in fruits, but optimization of irradiation parameters is necessary to balance antibacterial efficacy with fruit quality preservation.

Keywords: UV-C treatment; raspberries; strawberry; retain freshness;

Fig. 1. UV-C LED Beads: A. LED Strip with 35 UV-C LED Beads; B. LED Panel with 14 UV-C LED Beads;C. Two refrigerators at 4℃, one for control (no UV) and one for UV treatment

This study investigated the inhibitory effects of different UV-C irradiation patterns on mold spoilage in apple slices and raspberries. Under open natural environmental conditions (humidity 55%–60%, ambient temperature 22 –27 ℃, the effects of UV-C LED irradiation with varying time intervals on fruit mold spoilage were preliminarily explored. Four UV-C irradiation patterns were established: 0% (negative control, no UV-C irradiation), 25% (15 s on/45 s off), 50% (30 s on/30 s off), and 75% (45 s on/15 s off). The changes in apple slices and raspberries were photographed and recorded every 4 hours.

Fig. 2. Testing of UV-C LED Preservation Effects on Apples and Raspberries under Ambient Conditions: A. Oxidative State of Apple Slices; B. Preservation State of Raspberries

As shown in Figure 2A, the storage experiment results for apple slices over a 68-hour period revealed significant differences in preservation outcomes. The negative control group (0% UV-C) exhibited pronounced oxidative reactions, with extensive mold colony formation, severe dehydration of the cut surface and surrounding areas, and 50% of the apples showing signs of rot, indicating extremely poor preservation. The 25%UV-C group (15 s on/45 s off) showed some suppression of mold growth, with only a few mold spots observed; however, dehydration of the cut surface and surrounding areas remained significant, with evident moisture loss. In contrast, the 50% UV-C (30 s on/30 s off) and 75% UV-C (45 s on/15 s off) groups demonstrated markedly superior preservation compared to the previous groups. Both groups exhibited no significant mold spots, maintaining a high level of freshness, indicating that UV-C treatment within this dosage range effectively inhibits mold growth. However, all UV-C-treated groups displayed a common yellowing reaction on the apple cut surfaces. Notably, the 75% UV-C group showed greater dehydration at the edges of the cut surfaces compared to the 50% UV-C group, likely due to prolonged UV-C exposure elevating the temperature of the apple surface and surrounding environment, accelerating cellular moisture transpiration and evaporation, resulting in increased edge dehydration.

As depicted in Figure 2B, over a 78-hour storage period, raspberries subjected to different UV-C irradiation patterns exhibited significant differences in spoilage, mold proliferation, and moisture retention compared to the negative control group. The control group (no UV-C treatment) showed extensive spoilage after 78 hours, accompanied by substantial mold colony proliferation in the affected areas. The 25% UV-C and 50% UV-C ( groups displayed no large-scale spoilage, with only minimal mold spots observed in localized areas and significantly fewer mold colonies compared to the control group. Mold spot expansion in these groups was also notably slower. The 75% UV-C group exhibited the most pronounced mold suppression, with no mold spots observed on the raspberry surfaces, indicating complete inhibition of mold growth. However, high-dose irradiation led to noticeable moisture loss, with the raspberry flesh appearing slightly shriveled compared to the 25% and 50% UV-C groups.

These results demonstrate that apple slices and raspberries exhibit significant differences in oxidation, mold growth, dehydration, and spoilage, with suppression effects positively correlated with UV-C irradiation duration. The 50% UV-C ( and 75% UV-C irradiation modes provided the most effective mold suppression for both apples and raspberries. However, high-intensity UV-C irradiation increased photooxidation and compromised moisture retention on fruit surfaces. The 25% UV-C mode achieved the best overall performance in terms of antibacterial efficacy and preservation quality.

The experimental results showed that, in terms of raspberry preservation (Figure 2), after 78 hours, the negative control group exhibited extensive spoilage accompanied by significant mold colony proliferation. The 25% and 50% UV-C irradiation groups displayed only localized mold spots while maintaining relatively high freshness, whereas the 75% UV-C irradiation group showed no mold formation but experienced some dehydration. These findings indicate that UV-C irradiation has a significant anti-spoilage and preservation effect on raspberries, with the inhibitory effect positively correlated with the proportion of irradiation time. Among the tested modes, the 75% UV-C irradiation mode demonstrated the best mold suppression effect on raspberries; however, the high irradiation intensity of UV-C tended to induce changes in the fruit. The 25% UV-C irradiation mode achieved the best overall performance in terms of both antibacterial efficacy and preservation.

3.2 Preservation Effects of UV-C LED under 4℃ Refrigerated Conditions

This study evaluated the inhibitory effects of intermittent UV-C LED irradiation on fruit spoilage and mold growth in a simulated cold storage environment at 4℃. Based on observations from natural environment tests regarding fruit surface oxidation and dehydration under four different irradiation intervals, the experimental setup was optimized. The number of LED beads was reduced from 35 to 14, and the irradiation pattern was set to 25% UV-C (15 s on/45 s off) to lower the UV-C irradiation intensity while enhancing heat dissipation from the LED beads. Additionally, the distance between the LED beads and the fruit was increased from 20 cm to 40 cm. This 20 cm increase in height was implemented to reduce the oxidative effects of UV-C on the fruit surface.

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