Unraveling the Mysteries of Food Odors

Research on food odors by Sheryl Barringer, a longtime professor with the Department of Food Science and Technology at The Ohio State University, is helping scientists develop ways to reduce off-odors in plant-derived proteins.

During her 30-plus-year career in food science, Barringer’s extensive body of research has encompassed microwave heating, food safety, coatings, and tomatoes. That last topic—where she worked on the quality and viscosity of tomato products—was how she came to focus on food odors.

She’s researched off-odors in garlic, sunflower seeds, Swiss cheese, kefir, and other foods. Her recent research on plant-based yogurt formulated with plant-derived proteins has uncovered a novel way to reduce the odors that people find unpleasant, thus improving the odds that it will be consumed. “Because if it smells better, you’re more likely to eat it,” she says.

Flavor and odor are inextricably linked, explains Barringer, and her aim is to develop processes that provide more control over odors. “Those smells can be positive or negative,” she says. “We’re focusing on how to either decrease the negative smells or increase the positive odors.”

We’re focusing on how to either decrease the negative smells or increase the positive odors.

Sheryl Barringer

Department of Food Science and Technology, The Ohio State University

The Science of Smell

She’s found some interesting and surprisingly simple ways that off-odors can be modified. A fortuitous event changed an early project examining garlic off-odors. Barringer was working with a student who was helping measure volatiles associated with garlic breath. They were puzzled; something seemed wrong with their equipment because it was registering abnormally low levels of volatile compounds, but otherwise the machine seemed to be working properly. As the two were brainstorming possible causes, the student mentioned he’d eaten an apple an hour before doing the test.

At first, Barringer didn’t believe that something as simple as eating an apple would have such a dramatic impact on the volatiles. But they tested it anyway and found the apple was indeed influencing the garlic.

“That’s where we were like, ‘Wow, there’s this huge deodorization effect coming out of this apple,’” she says. She explains that the phenolics in the apple were responsible for the decrease in the volatile compounds that created the unpleasant smell.

More Fermentation, Better Results

That work on odors led to further research on the potential of various types of mint leaves, yogurt, and herbs to deodorize garlic as well as to her current project that explores how to decrease the off-odors of plant-derived proteins.

Food companies are fortifying their products with plant proteins, which often have been sourced from soy, Barringer says. But there’s also been recent growth in soy alternatives like pea, barley, and hemp proteins. Reducing off-odors isn’t simple because each plant protein has its own unique smell.

“Many of them have odor issues and flavor issues,” Barringer says. “Proteins are tough because they really like to bind up flavor.”

While there’s been research in this area, and some interventions do exist for this problem, none are completely effective, and they can also create other issues, including texture changes, she notes.

Fermentation can alter odor-causing compounds, making it a promising strategy for improving plant protein flavor. However, single-stage fermentation does not eliminate all off-odor volatiles, which prompted Barringer and her colleagues to investigate whether a two-stage process would be more effective. She and her fellow researchers chose vegan yogurt as the test product for the research. They prepared a variety of yogurts, each formulated with one of eight different plant-derived proteins, including soy, chickpea, hemp, and rice.

Lactobacillus plantarum was used as the first-stage fermentation bacteria, and commercial freeze-dried yogurt starter with Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus, and Lactobacillus acidophilus was used for the second stage.

The researchers found that two-stage fermentation significantly decreased the volatile compounds that create unpleasant odors for all eight proteins. The results were dramatic, Barringer says.

She thinks that the two-step fermentation process works better than single-step due to pH levels. During yogurt production, the pH will drop, which is “very important for the quality of the yogurt,” she explains. But that decrease in pH also suppresses some of the bacteria important for deodorization.

“Playing with that pH and not allowing the pH to drop quickly at the beginning was very important to the effectiveness of the deodorization,” she says.

Their results were supported by a sensory study the researchers did with 42 Ohio State students who tasted both fermented and non-fermented yogurts. The samples of nonfermented yogurts had strong off-odors and tasters rated them poorly, but the twice-fermented samples passed the test. Although the tasters said the two-step yogurt was bland, Barringer says the goal was to create a neutral base product that could be flavored.

Industry Applications

The process isn’t limited to yogurt. “There are much broader applications,” Barringer says. The researchers have received a provisional patent for their process, and they are in discussion with a food company to put it into production.

Barringer and her colleagues are now working on extruded meat analogs, using starches to bind the off-odors. As with the yogurt, their goal is to create a neutral-tasting product that could be customized with the addition of flavor, she says.