Soil microbes may shape the flavor and spiciness of food and wine

Serious wine aficionados often rave about the distinctive flavors in their favorite beverages, attributing the unique tastes to the soil in which the grapes are grown. This concept, known as terroir, refers to how a region’s natural environment – including its soil, climate, and topography – influence the flavor of wine.

But what about other crops? Can the microscopic organisms in the soil also play a role in determining the flavors of the foods we eat?

In a pioneering study, former PhD student Corrine Walsh and CIRES fellow Noah Fierer led researchers in exploring this intriguing question. The analysis was focused on one particular aspect of plant flavor: the spiciness of mustard seeds.

“I thought that was an interesting question,” said Walsh. “We know microbes and plants communicate via chemicals – could those chemicals impact plant flavor?”

Digging deeper: Soil microbes and food flavor

Previous studies have shown that soil characteristics significantly affect plant growth, disease resistance, and nutrient uptake. However, due to the complexities involved in isolating these effects, researchers have largely left the potential influence of soil microbes on plant flavor unexplored.

“It is often claimed that the types of microbes found in soil should influence crop flavor,” Fierer noted, highlighting the difficulties in studying soil microbes.

To address this, Walsh and Fierer employed a unique method. They conducted a greenhouse experiment, growing mustard plants with a liquid inoculum of microbes sourced from various Colorado environments, including aspen groves, sagebrush fields, ponderosa pine forests, and agricultural pastures.

To ensure that only the microbial variables were altered, the researchers maintained consistent conditions such as potting soil, temperature, watering, and nutrients.

The spice of life: Why mustard?

The researchers chose mustard for its simplicity to grow and its relevance in the Brassica family, known for producing vegetables with distinct spicy and bitter flavors like broccoli, cabbage, and horseradish.

These flavors primarily stem from glucosinolates, chemicals that defend the plants against pests and diseases.

“When you cook them they have that kind of sulfury smell. The glucosinolates have a sulfur compound in them, and that’s what you’re smelling when you cook,” noted Walsh.

The quest for spicy seeds

After harvesting, the researchers analyzed the mustard seeds for glucosinolate concentrations to measure their spiciness, instead of subjecting them to taste tests.

Although the experiment faced challenges due to the changing nature of the microbiomes, it revealed a connection between the microbiome and seed chemistry. However, the specifics of this relationship, including the direction and mechanisms, remain unclear.

Walsh reflected on the complexity of controlling biological variables. “The way the microbiomes diverged over time throughout the experiment made it hard to test some of our hypotheses of microbes affecting flavor,” she said. “We found a relationship, but the direction and mechanism of that relationship remain unknown.”

Future flavors: The potential of microbial probiotics

Despite these challenges, the study provided preliminary evidence that soil microbes might influence the spiciness of mustard seeds.

This discovery opens up exciting possibilities for using microbial “probiotics” to enhance other crop properties, such as drought resistance and productivity, potentially impacting flavor as well.

The research marks an important step in understanding the complex interactions between soil microbes and plant flavors.

“We do now know that microbes are worth considering in this venue. There is excitement about using microbial inoculants to do other things for crops,” said Walsh.

This ongoing exploration of microbial influence not only broadens our understanding of agriculture but also hints at future innovations in enhancing the flavors of our favorite foods.

Soil and food flavor

The soil in which food crops are grown can significantly influence their flavor. This effect is due to various factors, including the soil’s mineral composition, pH level, organic matter content, and moisture levels. 

These elements affect how the plants absorb nutrients and develop their compounds, which in turn can influence their taste, aroma, and nutritional value.

Certain minerals like selenium, zinc, and magnesium can enhance specific flavors in crops. In addition, the acidity or alkalinity of soil can affect how well plants take up nutrients, altering flavor profiles.

Furthermore, rich organic soil often leads to stronger, more robust flavors in vegetables and fruits.

The study is published in the journal New Phytologist.

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