Freshness and nutrition check for fruit & veg

University of Queensland researchers have developed a nanoprobe that changes colour to indicate how much vitamin C is in fresh produce and juice.

Dr Run Zhang from UQ’s Australian Institute for Bioengineering and Nanotechnology (AIBN) said the technology could be added directly to food and juice samples or applied to paper testing strips that, when touched to cut or intact produce, change colour to indicate the concentration of vitamin C.

Vitamin C — also known as ascorbic acid — is a critical antioxidant in most fruits and vegetables and can vary significantly depending on the length of journey from the farm to fridge.

“Things like exposure to heat, oxygen and light all accelerate vitamin C degradation, as does the quality of the soil or pesticide use during the growing process,” Zhang said.

“Measuring vitamin C is therefore an essential step for producers, regulatory agencies, and consumers who want to simply evaluate food freshness and nutritional content.”

The particle-sized probes designed by Zhang’s team consist of a metallic core coated with a fluorescent dye.

The coating is designed to break away in the presence of ascorbic acid and the remaining materials change colour to match the strength of vitamin C in a sample of food or juice.

PhD scholar Dihua Tian said the probes coloured yellow to brown when exposed to different fruits, vegetables and juices, providing a rudimentary indication of freshness and nutrition.

The simplicity and portability of the technology means a more accurate reading could be possible using a smartphone app.

“We see great potential for more user-friendly analysis,” Tian said.

“Ultimately this is technology that could be used in tandem with colour visualiser phone applications that can scan a testing strip coated in our nanoprobes and tell you exactly how fresh and healthy the food is.”

Zhang said the nanoprobes also had potential applications in agriculture.

By testing plant leaves for vitamin C content, he said producers could gain insights into plant nutrition, stress responses and optimal agricultural practices.

The research is published in Food Chemistry.

Images: Supplied