Sour Times For Florida’s Citrus

DESSA: I’m Dessa, and this is Science Friday.

Florida is known for citrus, particularly its fresh-squeezed orange juice. But citrus in Florida is struggling. For the last two decades, crops have been struck with a devastating disease, called citrus greening, and Florida orange production has dropped some 94% in the past 20 years.

Citrus greening is caused by an invasive insect, the Asian citrus psyllid, and it’s threatening to wipe out the citrus-growing industry in the state. Scientists are hard at work, devising a myriad of possible solutions to save Florida’s citrus crop. And joining me now is one of those scientists, Dr. Yu Wang, associate professor of Food Science at the University of Florida’s Citrus Education and Research Center, based in Lake Alfred, Florida.

Dr. Wang, welcome to Science Friday.

YU WANG: Thank you. Thank you for your introduction.

DESSA: OK, can we just start with the basics of the problem? So how does an insect cause citrus greening?

YU WANG: Actually, citrus greening disease is a bacterial infection disease. So the bacteria, we call it CLas. And the insect carry the bacteria and transmit it to the trees in Florida.

DESSA: I’ve seen images online. It’s kind of icky. It looks as if the infected plants have been covered with somebody shaving Parmesan cheese, as you would over a salad. And it affects the way that the fruit tastes, as well, on those infected plants. Is that right?

YU WANG: That’s right.

DESSA: Yeah, how do they taste?

YU WANG: Well, the fruit tastes sour, less sweet, sometimes with bitterness. And the aroma, like the very typical sweet orange aroma, decreased a lot.

DESSA: You’re one of many scientists who are working to try to solve this problem. And I know that some teams are working on curing the disease and others are focusing on breeding disease-resistant plants. And you’re working to solve the citrus greening problem by mapping the universe of citrus sweetness itself. Can you explain how your research is focused on flavor modulators? What is that?

YU WANG: Most consumers like sweet or sweeter things. So for our study, we would like to detect many different varieties and to find out what varieties actually could provide that very sweetness perception. But at the same time, because our consumer is also concerned about the health benefit related to too much sugar consumption, therefore, we are looking for this flavor modulator. We try to find a certain kind of compound, obviously, that are not sugar, which can enhance the sweetness perception.

DESSA: OK. So when you use that term “flavor modulator,” it sounds like sort of a companion substance to the other flavors that we perceive, is that right?

YU WANG: Let’s just say some aroma compounds, like some very citrusy aroma, they have that natural characteristic to enhance the sweetness. But there are also some other compounds like the sweetener we’re talking about– Stevia, for example, that’s kind of a natural sweetener– so there is some sweetener existing in the citrus, and it could also provide that sweetness perception.

There are also some other compounds that are tasteless. So when you mix those compounds with sugar, they somehow enhance the sugar sweetness perception.

DESSA: OK. And which of these flavor modulators are at play in the citrus world?

YU WANG: Well, so far, we have identified certain flavonoid-based structure compounds. And those compounds, they either taste sweeter or they could enhance the sweetness of sugar.

DESSA: How do you go about trying to solve the problem of these infected citrus trees? How do you apply that research to the problem at hand in Florida?

YU WANG: There are two major varieties have been used for juice processing. And right now, due to the quality change and less sweetness in the juice from those two varieties, our idea is to blend more varieties into our juice pipeline so those new varieties can be used in blending in some varieties we are considering containing those sweetener, or sweetener enhancers. So that somehow, when we blend those varieties with the current variety, it could increase the sweetness perception, but at the same time it won’t increase too much sugar in our juice product.

DESSA: Is that done only with healthy plants, or is it also the case that you’re finding that some of the research you’ve done is useful for growers who already have infected crops?

YU WANG: Well, yes, a certain variety right now growing in the ground also contain those sweetener. So right now the question is how much we can increase those sweetener and sweetener enhancer in the current existing variety. So that’s probably needs some specific pre-harvest treatment or a different combination of nutrient treatment, but that research is an ongoing research.

DESSA: I know that you’ve studied all different types of citrus in your work. Do you think that we’re likely to see more varieties of orange juice, citrus juice, on the shelves sometime soon?

YU WANG: Well, definitely, that’s what we hope for. Our breeding team at the University of Florida, they are having– I don’t know how many– maybe 10,000 or even more than 10,000 varieties. But in the market, there are probably just like three or five varieties. So you can think about the potential.

DESSA: OK. So before I let you go, can I bother you for an inside tip? What is the sweetest, best orange juice that I’m not yet looking for on the market?

YU WANG: Well, like I said, right now, orange juice are using two varieties, Hamlin and Valencia. So the juice is blended with probably 20% Hamlin and 80% of Valencia. So Valencia is a very sweet and aromatic variety.

DESSA: Thank you so much for your help in helping us understand this issue and the work that’s being done to address it.

YU WANG: Thank you.

DESSA: Dr. Yu Wang, associate professor of food science at the University of Florida’s Citrus Education and Research Center, based in Lake Alfred, Florida.

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