Scientists in Canada have developed a plasmonic colorimetric test to determine the flavour quality of maple syrup. The test can indicate when the syrup is off-flavour in minutes by changing colour from red to blue.

Organic molecules responsible for the distinctive flavour of maple syrup comprise only 1% of maple syrup content, and these molecules vary over the harvesting season. Compounds such as amino acids and thiols, which cause inferior flavours increase as spring progresses. At present, current quality control checks take place at centralised facilities and require trained technicians to taste the syrup or perform fluorescence spectroscopy experiments. A rapid objective test that harvesters can use where they produce the syrup at maple sugar shacks is lacking.

An image showing bottles of maple syrup

Source: © Shutterstock

Now, Jean-Francois Masson and his colleagues at the University of Montreal have developed a plasmonic tongue sensor for doing just that. The sensor contains a gold nanoparticle solution and when compounds associated with off-flavour syrup are present, these nanoparticles aggregate by interacting non-specifically with the flavour molecules. This causes plasmonic coupling of the nanoparticles so that their resonance wavelength shifts, leading the solution to visibly changing colour.

To verify their sensor, the group adapted their test to high-throughput conditions and studied 1818 syrup samples with various flavour profiles and colours from different regions of Canada. It identified 98% of the off-flavour samples. Trialling the basic colorimetric test on-site, they showed that non-technical staff could use it on most syrup samples, and any debatable results could be checked with a portable spectrophotometer.