Pesticide-Free? New Technology Using "Flashing UV-C" to Extend the Shelf Life of Guava

Pesticide-Free? New Technology Using "Flashing UV-C" to Extend the Shelf Life of Guava

The fruit bought at the supermarket is suddenly covered with black spots. It was supposed to be delicious, but due to its appearance and spoilage, it ends up being thrown away. A prime example of such "waste" is the fragrant tropical fruit, guava. Guavas are prone to damage due to the shocks during distribution and their handling difficulties, allowing pathogens to enter and making them susceptible to anthracnose post-harvest. As a result, it is estimated that 20-40% of the total production is lost in developing countries.


The True Nature of Black Spots: Anthracnose Appears "Post-Harvest"

The troublesome aspect of anthracnose is that even if it is not noticeable in the field, symptoms can rapidly progress post-harvest. The cause is a group of microorganisms belonging to the Colletotrichum gloeosporioides complex. They create dark lesions on the fruit skin, significantly reducing its market value. While lesions typically appear on the surface, they can also reach the flesh through tiny wounds caused by insect damage, improper handling, or mechanical damage during transport.


The Mainstay Until Now: "Post-Harvest Chemicals"

The main countermeasure has been "post-harvest pesticides" (primarily fungicides) where fruits are immersed in or sprayed with chemical solutions immediately after harvest. They are then dried and stored in refrigeration. However, chemical agents come with concerns about residues and environmental impact. Researchers at the Brazilian Agricultural Research Corporation (EMBRAPA) have pointed out that chemicals used in post-harvest treatments can adversely affect human health (especially children) and the environment, aiming for "clean and sustainable technology that maintains food integrity without residues."


Introducing: Pulsed UV-C Instead of Continuous

The core of this research is the use of UV-C (short-wavelength ultraviolet light used for sterilization) in a "pulsed" manner rather than "continuous irradiation." In other words, instead of continuously shining light, it is turned on and off at regular intervals. This design aims to inactivate pathogens while minimizing excessive stress on the fruit's skin and reducing energy loss.


Device Innovations: Mirrors and Three Lamps to Reduce "Irradiation Unevenness"

The processing device used by the research team features a cylindrical structure with mirrors and three UV-C germicidal lamps inside.

  • One lamp emits light perpendicular to the structure's surface, creating a "cylinder of light."

  • Another lamp is directed towards the mirror, illuminating the guava with reflected light.

  • The third lamp directly irradiates the fruit.


This combination ensures that the fruit surface receives as much UV-C as possible, reducing missed irradiation. The absorbed radiation is converted to heat on the surface, leading to microbial inactivation.


Not Just "Sterilization": The Concept of Activating Fruit Resistance

Interestingly, the approach goes beyond merely "killing bacteria" and delves into the fruit's defensive responses. Researchers state that modulated UV-C allows precise control of the interaction between light and fruit, minimizing damage to the skin while reducing light energy loss. As a result, not only are pathogens suppressed, but the fruit's natural resistance mechanisms are "activated," extending shelf life while maintaining quality.


Effectiveness Varies with Conditions: The Key is Modulation "Frequency"

According to summary information from external databases, the control of anthracnose depends on modulation conditions, with certain settings (e.g., 0.99 kJ m−2/30 Hz) being particularly effective. This suggests that not just any UV-C will do; the way it is pulsed likely affects the balance between effectiveness and quality retention. For practical implementation, optimization according to factors like fruit ripeness, variety, surface condition, and processing throughput (amount processed per hour) will be crucial.


However, Currently "Promising in the Laboratory": The Next Step is Line Demonstration

However, the results were obtained in a laboratory environment. The next step is to verify whether the effects can be realized under "real-world conditions" at actual production facilities and adapt the equipment to the fruit processing line. In the transition from the lab to the field, factors that can affect efficacy, such as temperature and humidity, adhering dirt, individual fruit differences, and posture during transport, increase significantly. Clearing these hurdles is essential for the technology to evolve into a "usable method."


Expected Impact: Balancing Loss Reduction and "Zero Residue"

If practical implementation progresses, the expectations are high.

  • Reducing Food Waste: Reducing the instances of unsold, uneaten, and discarded fruit due to black spots.

  • Reducing Dependence on Pesticides: Decreasing the frequency of post-harvest chemical treatments, alleviating concerns about residues and environmental impact.

  • Enhancing Transport and Export: Longer shelf life makes it suitable for long-distance distribution and export.

  • Application to Other Fruits: Potential application to fruits with similar fungal diseases.


While UV-C as a "clean physical treatment" has been known for a long time, the key point this time is the simultaneous pursuit of quality and suppression effects through "modulation (pulsing)" and "irradiation efficiency design."


Reactions on Social Media

  • "If it extends shelf life without pesticides, that's great. Residues are a concern, especially for fruits given to children."

  • "Hearing about UV is worrying, but if it doesn't leave residues with surface treatment, it might be reassuring."

  • "It's interesting how just pulsing can change the effect. Optimizing frequency sounds like engineering."

  • "Can it be implemented on-site? Keeping up with the processing line speed is crucial."

  • "Depends on the cost. If the equipment is expensive, it might end up being a technology only for large-scale farmers."

  • "I'd be happy if it could be applied to other fruits like mangoes and strawberries."

  • "The idea of not just 'sterilizing' but also enhancing the fruit's resistance feels futuristic."


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