Deliberately inducing stress

The plants use these substances to attract insects or fend off microbes such as viruses, fungi or bacteria. They produce the bioactive substances when they are, among other things, under stress such as from too much sun. “For example, plants cannot put up an umbrella to protect themselves from too much ultraviolet light and therefore form secondary metabolites that absorb the ultraviolet light,” explains Wiese-Klinkenberg. The Jülich scientists want to produce such stress reactions in a controlled manner so that the plant produces more secondary metabolites and the residual mass from production is upgraded. The scientists already conducted initial experiments with tomato plants in a previous project of the Bioeconomy Science Center (BioSC), the research cluster for sustainable bioeconomy in North Rhine-Westphalia.

Now it’s paprika time. The Jülich researchers are initially concentrating on two of the more than 100,000 known secondary plant compounds: the flavonoids cynaroside and graveobioside A. “However, we also want to analyse the paprika leaves for other interesting ingredients.”

In recent years, the number of patent applications involving the substance cynaroside has increased. “We therefore assume that cynaroside is an ingredient with promising market potential for the cosmetics and pharmaceutical industries,” explains Wiese-Klinkenberg. Graveobioside A is known to act against insect egg deposition: In the long term, it could be used as a natural biocide.

TaReCa

The acronym stands for the joint project “Tailoring of secondary metabolism in horticultural residuals and cascade utilisation for a resource efficient production of valuable bioactive compounds”. TaReCa is funded by the Federal Ministry of Education and Research.

In order to stimulate the production of the two substances, the scientists put the plants under stress in climatic chambers: with common salt in the nutrient solution, with low temperatures and ultraviolet light, or they deprived them of their nutrients. “The salt stress was the most effective. Through the combination of salt addition and other stress factors such as cold, we have succeeded in increasing the cynaroside content in the leaves tenfold. That was a surprising success,” says the researcher excitedly. The researchers were also able to measure a triple increase in the concentration of graveobioside A in certain salt stress combinations: “We get about 20 milligrams of graveobioside A per gram of dry weight. That’s a good yield.”

The scientists are now working on improving the coordination of the interaction between optimal salt dosage, treatment duration and various stress factors, because “too much” means that the plant dies and drops its leaves, “too little” means too little yield. “In addition, the vegetable farmer also needs a measurement method to control how stress works,” says the researcher. “For this, we use non-invasive methods with photos and colour analyses as the colour of the leaves, for example, changes with the stress.”

Vegetable farmers in particular could benefit from these research approaches: they sell not only the fruits, but also the accessory agents from the rest of the plant. “In order to assess the market potential of individual ingredients and possible areas of application, the TaReCa joint research project involves not only plant researchers, horticulturists and process engineers from the BioSC, but also economists,” explains Wiese-Klinkenberg. For example, they can calculate whether the farmer should dry the leaves and stems himself or whether a large contractor should collect them: the drying process would significantly reduce transport costs, but the vegetable farmer would have to invest in a drying oven.

TARGETING NOT ONLY PEPPERS

The peppers in the salad, the flavonoids extracted – what remains is the fully exploited pepper plant, which no longer ends up in the compost, but in a biorefinery, where it is converted into platform chemicals for many other industrial products and has, thus, finally completed its service. The value chain is thus extended, economic added value is generated and a valuable substance is produced in a resource-saving manner – an example of a successful bioeconomy. And this not limited to the peppers. “Long term, we want to apply the new processes and technologies to other horticultural plants,” says Wiese-Klinkenberg. Her next favourite: the cucumber.

Katja Lüers