Fruits and vegetables are expensive enough without them going bad quickly on the kitchen counter or even in the refrigerator before we’ve even had a chance to eat them. Extending their shelf life has long challenged science.

Now, doctoral student Belal Abu Salha at the chemistry department at Bar-Ilan University (BIU) in Ramat Gan has developed a process of coating fruits and veggies with edible nanoparticles using sonochemistry. His research began at his family’s strawberry nursery on the Golan Heights, where he often wondered how he could prolong the freshness of the fruit from the moment picked until the moment eaten.
“I used sonication – a process of applying ultrasound energy in a liquid, to develop nano-coated particles from chitosan. Chitosan is a natural substance derived from polymers such as chitin, polysaccharides, and proteins,” explained Abu Salha.
It is used for a medical dressing on the battlefield and high blood pressure, high cholesterol, obesity, wound healing, and many other purposes, but so far there is no good scientific evidence to support many of these uses.“Sonochemistry allows the chitosan particles to embed into the surface of the fruit and coat it quickly and efficiently, and the coating significantly decreases the damage to the fruit caused by fungi and bacteria.”
The process can be used as a safe substitute for current methods to preserve produce. The coating significantly reduces damage caused by bacteria and fungi, thus extending shelf life and preserving fresh taste and quality. In addition, chitosan is environmentally friendly and biodegradable.
Chemistry Prof. Aharon Gedanken developed the sonication method and advised Abu Salha on his research. “When you bombard a liquid solution with high-frequency sound waves in a process called ultra-sonication, the solution swirls rapidly, and masses of microscopic bubbles are formed that collapse into themselves. When the collapse occurs near a solid surface, like a strawberry or even a millimeter grain of material, liquid streams move to the surface of the solid at a very high speed and toss the particles from the solution onto the surface at enormous speeds. The particles are embedded in the solid and cannot be removed, even by washing it. In this way, it’s possible to assign a solid with properties it didn’t have in the first place – antibacterial properties or resistance properties, for example. This is how antibacterial substances can be embedded in fruits and vegetables or any other material.”
A vendor stands behind a cart as he sells strawberries at a market in Jerusalem's Old City (credit: RONEN ZVULUN/REUTERS)
A vendor stands behind a cart as he sells strawberries at a market in Jerusalem's Old City (credit: RONEN ZVULUN/REUTERS)
During the research process, the chitosan solution underwent a sonochemical process, and the sound waves caused the creation of edible nanoparticles with antibacterial properties that were embedded on the surface of the strawberry, Abu Salha noted. “Then I tested the antibacterial activity of the strawberry and the physical and chemical properties such as the sugar level in the fruit, acidity, and spoilage rate. I discovered that the shelf life of the strawberries treated with edible nanoparticles of chitosan was extended by an impressive 15 days.”
Abu Salha’s discovery has tremendous implications for his family’s strawberry business in the Golan. Through sonochemistry and its innovative approaches to green chemistry, this research facilitates the discovery of easy, efficient, and environmentally friendly solutions and their application in the food preservation industry. Abu Salha’s innovative approach will allow for the preservation of other fruits, vegetables, and fresh foods for a longer period and prevent fungi and bacteria from affecting their quality.