Workshop participants compare flavor nuances of different varieties of raisins dried either on the vine or on the vineyard floor.

Flavor is the final frontier

In terms of quality, scientists are now going where the fruit and vegetable industries haven’t ventured before. They are researching the vast and mysterious world of flavor, according to Diane Barrett, the UC Cooperative Extension fruit and vegetable products specialist at UC Davis.

In selecting fruit varieties, comparing cultural practices and studying storage and transportation, scientists have focused on texture, appearance and nutrition, while flavor has been on the back-burner, until now.

Barrett and Sue Ebeler, a professor in the UC Davis Department of Viticulture and Enology, recently hosted a workshop at UC Davis to share flavor research with members of the fresh produce and processed fruit and vegetable industry.

“It’s important to understand flavor to develop better methods for analyzing food flavor and to understand the effect of cultural practices in agriculture, processing and storage on flavor,” Ebeler said.

Flavor is composed of aroma, taste, appearance and mouthfeel. It involves multiple sensory tools and multiple disciplines, said Ebeler, whose research focuses on the development and application of analytical techniques to study wine flavor chemistry.

Ebeler uses gas chromatography to dissect aromas that waft from glasses of wine. A tiny fiber is suspended over the wine to collect the volatiles that make up its scent. The scent molecules are sent through a very long, very thin coiled tube lined with a variety of coatings to which certain molecules adhere. A computer analyzes where along the tube compounds are found and produces a graph showing the levels of those compounds.

A glass of chardonnay, for example, might release volatile compounds that are responsible for hints of lime, butter, toast, melon and nuts, Ebeler said. Electronic sniffing has allowed scientists to determine the compounds responsible for these aromas. Butter scent, for instance, can be attributed to diacetyl. However, there are other aromas that are more difficult to pin down. A single compound cannot be credited for aromas like lemon, apple, pear, peach, caramel and pineapple, Ebeler said. They emanate from complex interrelationships of various volatiles.

“We now know there are more than 1,300 volatile compounds identified in alcoholic beverages alone,” Ebeler said. “For some of them, such as ‘musty cork’ or ‘rose,’ it only takes a few parts per trillion to smell them.”

When it comes to certain flavors and aromas, sensory descriptive analysis is the best way to characterize specific attributes. In descriptive analysis, a panel of judges works together to decide upon an objective description of an aroma or flavor. The gas chromatographic profile of the aroma is then also determined, and peaks in the amounts of certain chemicals are compared to the judges’ sensory descriptions.

Cabernet sauvignon, for example, may emit aromas of floral, apple, honey, chocolate, dried fig and tobacco to the human judges. By analyzing the samples electronically, high levels of certain chemicals could be indicators of these pleasant scents.

“This is correlation, but it doesn’t mean cause and effect,” Ebeler said. “Many compounds have little sensory impact and many compounds with important sensory properties can’t be measured.”

Research aimed at allowing the scientists to develop a complete understanding of the relationship between sensory perception and analytical flavor composition is continuing.

Sensory studies require training

UC Davis professor Hildegarde Heymann has been working in the sensory science arena for 25 years. She notes that, because human taste preferences are highly variable, accurate sensory analysis requires a very large pool of tasters. And since an individual consumer’s taste is influenced by culture, psychology, and even genetics, an important step in taste analysis is training.

“We have to teach them the language. We do that with reference standards, such as chemical compounds, food products and verbal descriptions,” Heymann said.

In recent taste studies Heymann has conducted with UC Davis students, the subjects compared different varieties of raisins dried either on the vine or on paper trays spread on the vineyard floor. Heymann and her staff worked with the tasters for weeks to get the group to agree what exactly they would mean when they judged a fruit “astringent” or “gritty” or “sweet.” Heymann’s taste testing experiments were able to provide helpful results, however, she advises businesses that wish to use sensory analysis to make decisions that could have significant economic consequences to be very careful about gathering their information.

“Consumer panels are easy to conduct, but if they’re not the right people, the results are meaningless,” Heymann said. “If you work with a product, you probably know too much about it to do an objective study on its sensory properties. If I had to do a consumer panel, I would involve experienced consultants.”

The wine industry is ahead of fresh and processed fruit and vegetable industries in the area of flavor analysis, but in an increasingly competitive environment and with more consumers willing to pay a premium for convenient, healthful foods, pursuing sensory studies will be worth the effort, according to Barrett. 

“The flavor of fresh produce depends on many factors,” Barrett said. “Plant genetics, bio-chemistry, harvest maturity, postharvest handling and processing all play a role. But producers are beginning to notice that shelf life may not be the same as flavor life and that flavor is worth their attention.”

(May 2007)

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