Genuine maple syrup is a delight for the taste buds, whether you prefer light golden varieties or strong dark syrups. But sometimes batches can have unpleasant flavors. Scientists at the University of Montreal in Quebec, Canada have developed an artificial "tongue,quot; using gold nanoparticles that can eliminate bad batches from the start. It is not so much an electronic device as a simple portable chemistry test that detects a color change when there is an unpleasant taste in a sample, according to a recent article published in the journal Analytical Methods.
"Especially here in Canada, we take maple syrup for granted," said co-author Jean-François Masson of the University of Montreal. "But it is much more complicated than we had anticipated. It has some of the same complexities as good wine and whiskey." Quebec is the largest producer of maple syrup, accounting for about 70 percent of the world's supply.
It is not referring to cheap imitations whose main ingredients are high fructose corn syrup and imitation maple flavoring. To be considered a true maple syrup, at least in Canada, a product must be made entirely of maple sap collected from maples, usually varieties of sugar maple, red maple, or black maple. Maple syrup is primarily sugar, water, and a small amount of organic molecules that are responsible for the flavor profile of the final product. Those compounds make up just 1 percent of the content, but it's a crucial 1 percent, determining whether a given syrup is caramelized, smoked, salted, or woody, among the approximately 60 possible categories.
Maples store starch in their roots and trunks before winter, which turns into sugar. In late winter or early spring, as the sap rises, it can be collected by drilling holes in the logs and inserting a nozzle to channel the sap into the containers. The sap is boiled in pure syrup in a "sugar shack,quot;, typically a shack on top to let off steam. ("It is a cross between Daniel Boone's shack and a candy factory," Masson said.) After boiling, the syrup is filtered to remove any crystalline sugar that has formed (also known as "sugar sand,quot;).
Since 2014-2015, the United States and Canada have adopted roughly the same rating standards. The test is usually done after filtering, while the syrup is still hot. Grade A syrups are those sold for consumer use – the things you pour on your pancakes, waffles, etc. If a lot does not meet the criteria, it is considered to be process grade and cannot be sold in containers of less than five gallons. Otherwise, the batch will be considered deficient.
The Grade A category includes golden syrups, amber, dark and very dark syrups. Color classification is determined by measuring the internal transmittance of a syrup by passing a wavelength of light of 560nm through a 10mm sample. For a golden syrup, there must be 75 percent or more transmittance. A very dark syrup (typically used for cooking or baking) will have a transmittance of less than 25 percent.
When a batch is found to have unpleasant tastes, it is usually due to some type of contamination, microorganisms, or fermentation by-products, for example. One of the most common is the "friend,quot; flavor. A late harvest can alter the chemistry of the sap, resulting in higher levels of amino acids and small organic thiols. This, in turn, can affect the flavor profile. It is a situation that has been exacerbated by climate change, according to Masson, as Quebec now regularly experiences large temperature changes from day to day. "For example, one day there were snowflakes, which is unusual in May," he said. "The day before that, we were in the upper 60s. That is not good for producing maple syrup."
Masson's expertise is in developing field deployable instruments, which is why Quebec maple syrup producers approached him about the possibility of a quick and easy test to remove batches of flavorless flavors on-site . The current method of classifying and classifying syrups involves trained human taste testers that are rarely augmented in high-tech industrial settings with fluorescent spectroscopy. But there are only four such facilities in the world, according to Masson, and spectroscopy is not available to smaller producers. Fluorescent spectroscopy also cannot be easily implemented in the field.
Masson thought that a colorimetric test would be suitable for this application, and decided to use a plasmonic sensor, which can be configured for naked eye detection and would be suitable for the high performance 96-well plates used in maple sugar shacks. Plasma-based "noses,quot; and "tongues,quot; have been used to distinguish between normal cells and cancer cells, for example, or between different types of proteins. A 2019 article even reported on using a plasmonic-based matrix to detect different Scottish whiskey signatures.
Masson and his team designed their artificial "tongue,quot; to react specifically to "friend,quot; flavor profiles. They used spherical gold nanoparticles stirred in ultrapure water to create a reagent solution. Several molecules that are believed to be associated with unpleasant flavors in maple syrup also bind to golden surfaces. Therefore, if they are present in sufficient concentrations in a sample of maple syrup, they will cause the gold nanoparticles to clump together, causing a marked change in resonance wavelength and a corresponding visible change in color.
"It is similar to the pH or chlorine test that people regularly do to make sure the pool is not too alkaline or too high in chlorine," Masson said. "It will change color based on flavor profile. Therefore, it is a simple test at a glance that tells you whether or not you have changed, for example, from premium premium maple syrup to one with a slightly different flavor profile. "
To test maple syrup with the artificial "tongue,quot;, the user simply pours a few drops of syrup into the gold nanoparticle reagent. After 10 seconds, the reagent must remain in the red spectrum, indicating a higher quality syrup, or it will turn blue, which means that the syrup has that "friendly,quot; flavor and must be classified as a Processing Grade. The team validated their method by field testing 1,818 maple syrup samples from the 2018 harvest season produced by sugar shacks from various regions of Quebec. Those lots had already been officially classified; Plasmonic language results were compared to official grades to see how well it could detect flavors.
The test method works well in the field as a quick read, although there will always be a subjective element when it comes to color determination at a glance. Not only are there subtle differences in tones, which can be difficult to detect, especially near the transition point, but anyone who is color blind will find determination to be a challenge. Very dark maple syrups were also challenging. So Masson's group is developing a portable spectral photometer to magnify their plasmonic tongue, thus ensuring accurate readings.
That said, artificial language is not as sophisticated as human language. It is specifically designed to eliminate obvious batches of "friends,quot; so that producers know whether or not to produce, depending on the quality of the sap or syrup being made. Teams of human taste testers are still needed to qualify and classify the remaining batches. "Maple syrup is the same as wine," said Masson. "You do not want the wine to be classified according to whether a robot decides whether it is superior or low quality, since it can lose that sensation in the mouth that is so pleasant to us."
DOI: Analytical Methods, 2020. 10.1039 / C9AY01942A (About DOIs).