Strawberries under a high-tech magnifying glass

Strawberries are one of the most popular berries in the world due to their sweet taste and healthy composition. The complex biochemicals (biomarkers) that determine their taste and nutritional value can only be determined in detail by experts using modern analytical methods.

A team from Bergakademie, Technical University of Freiberg, in collaboration with Serbian colleagues, has for the first time used ultra-high resolution mass spectrometry to analyse different strawberry cultivars and determine how biomarkers are distributed in the fruit. The chemists found that most of the biomarkers are located in the strawberry's red skin.

The team published their results in the journal Neuroscience. Wiley Analytical Sciences And plants.

For example, a research team led by Dr. Jan Zuber of the Technical University of Freiberg identified a biomarker called pelargonidin-3-O-malonylglucoside in strawberry skin.

“These molecules have antioxidant properties. In the human body, these compounds bind free radicals and exert anti-inflammatory and vascular protective effects,” explains a researcher from the Institute of Analytical Chemistry.

The analyzed strawberry varieties also contain other biomarker molecules such as organic acids such as citric acid and sugars such as glucose. Depending on the concentration and ratio of these biomarkers, the flavor and nutritional value of each strawberry variety is determined. Most of these biomarkers are also found in the strawberry skin.

Thin strawberry slices for detailed analysis

The team was able to detect the concentrations of biomarkers in the strawberries so precisely thanks to a high-tech analytical tool called an ultra-high resolution mass spectrometer, which the researchers used to examine the slices. Here, the biomarkers are first converted by a laser into charged particles called ions, which are then separated according to their mass and number of charges.

“Our analysis makes it possible for the first time to distinguish between different biomarkers whose masses differ only by six decimal points.” The biomarkers are represented by a color-coded image of the signal measured from a thin strawberry slice.

“This clearly indicates that biomarkers related to fruit taste and quality are present in particularly high concentrations in strawberry skin,” Zuber says.

Targeted breeding of strawberries

Dr. Jan Zuber's team, together with researchers from the University of Belgrade in Serbia, used this method to investigate a total of 25 new strawberry varieties. “Since these biomarkers determine the taste and quality of strawberries, it is interesting for the breeding of strawberry varieties to know exactly where they are and in what concentration,” says the chemist.

“These findings can be used to select the highest yielding and most nutritious fruit varieties for production. Meanwhile, the results will also help us evaluate the acceptability of new fruit varieties to end consumers.”

Analysis of samples by mass spectrometry

The samples used for the analysis are only a few micrometers thick. Using a special cutting device (cryomicrotome), they are prepared for measurement in a mass spectrometer. This ultra-thin disk is then coated with a UV-active matrix, which is necessary to convert the various biomarkers into their corresponding ions.

The researchers then place a measurement grid over the specimen: each point of this grid is excited by the mass spectrometer's laser and the resulting ions are detected. Thanks to the ultra-high resolution of the mass spectrometer, even small differences in mass between biomarker ions can be detected and used to distinguish them.

The information obtained is evaluated and visualized using distribution images, showing which biomarkers can be detected in which areas of the thin section.