Tapping Into the Sweetness of Citrus

Many foods are getting sweeter. However, while our taste buds may like sugar, our bodies, not so much. Too much sugar in diets is linked to heart disease and other health problems, including diabetes.

There are many artificial sweeteners available, but they often have an unpleasant aftertaste that impacts a product’s overall palatability. Additionally, they don’t satisfy consumers’ preference for natural ingredients. And even natural sweeteners sometimes have undesirable flavors, and they can be difficult or expensive to source.

The quest for a sweetener that ticks all the boxes prompted researchers at the University of Florida’s Institute of Food and Agricultural Sciences to examine citrus fruits to see whether they could identify a novel natural sweetener. They chose citrus because studies from the 1960s had identified a compound that causes sweetness in lemon and orange leaves and also because citrus fruits are popular and a major crop in the United States.

“People consume a lot of citrus fruits and juice, but some consumers have concerns about sugar in citrus even though the sugar is natural,” says Yu Wang, a University of Florida associate professor of food science and the leader of the research project. “We are trying to identify sweeteners in certain varieties of citrus so we can develop a new variety of naturally occurring sweeteners that could be used in other foods or beverages.”

The researchers worked with 11 different fruits, including a variety of oranges, clementines, and grapefruit. The fruit samples were freeze-dried, and then slowly thawed. They were peeled and juiced, and the juice was turned into a powder using a freeze dryer. The powders were then mixed with several chemicals. To identify the compounds that cause sweetness, the scientists used targeted and untargeted metabolomics analyses, a relatively new method of measuring and analyzing cellular metabolites. They selected this approach, says Wang, because they needed a method with high sensitivity given that sweetness levels can vary widely from one type of citrus fruit to another.

The analysis yielded eight sweeteners or sweetness-enhancing compounds, seven of which the researchers were the first to identify in citrus. The standout was a compound called oxime V.

Sweet Synthesis

Oxime V already exists as an artificial sweetener and was originally synthesized in Japan, but this project marked the first time a natural version was identified. “We found that compound in citrus, which means that the compound actually exists in nature,” says Wang. Given the popularity of citrus fruit, she sees “huge potential to use that compound for the food or beverage industry in the future.”

The research findings could be useful for citrus breeding programs as well because new fruit varieties could be developed that are sweet but have less sugar while maintaining palatability, Wang says.

The researchers’ next step will be to identify the biosynthetic pathways of these compounds in order to synthesize them for use in food and beverage applications. “We want to understand what gene or what protein actually controls those compounds,” Wang explains.

The scientists also are planning follow-up research to find out why different fruits contain different amounts of some compounds, and why those harvested in 2019 had different compound levels from those picked in 2020. The disparity could be caused by environmental factors, including sun, water availability, and temperature, they conjecture. “We want to know, besides the genetic levels, what in the environment could affect the level of those compounds’ formation in nature,” says Wang.

TO LEARN MORE

“Natural Sweeteners and Sweetness-Enhancing Compounds Identified in Citrus Using an Efficient Metabolomics-Based Screening Strategy”

“The sweet danger of sugar”

“Added Fructose: A Principal Driver of Type 2 Diabetes Mellitus and Its Consequences”