Cornell University food scientists said that despite state-of-the-art chemical analyses, they still do not know why fresh-squeezed orange juice tastes better than the canned, bottled or frozen versions.

They have, however, been able to rule out limonene, a volatile (rapidly evaporating) substance in the oils of fresh-squeezed juice that most processors had thought accounted for the difference. However, they have isolated several other volatile elements that do seem to account for the flavor difference.

Limonene accounts for more than 90 percent of the amount of volatile compounds in fresh orange juice. Processors presumed its rapid evaporation during processing was the problem. They had sought ways of minimizing its loss but were never able to keep the fresh-squeezed flavor. An additional problem is that limonene is easily absorbed by plastic, which lines most packaged juice containers.

The role of limonene seemed plausible because food researchers knew that much of the perception of a food's flavor depends on aromas smelled while eating or drinking.

For example, people with no sense of smell have difficulty tasting the difference between orange, apple and grape juices. (Holding your nose while drinking will simulate the effect somewhat, but some of the aroma reaches the nose from the back of the mouth. Color and texture are also cues.)

The Cornell researchers, Anna Belle Marin and Terry E. Acree, disproved the limonene theory by asking volunteers to sniff several odors issuing from a special analytic device that separated out the chemical components of juice and pumped them out one at a time. Although limonene at high concentrations has a lemony smell, volunteers could barely detect it at the levels that exist in juice.

Many other substances, though present in much lower concentrations, turned out to have stronger odors and to contribute more to the flavor of orange juice. The relative contributions of these are still being worked out as are ways of either preserving it in packaged juice or fortifying the juice with synthetic versions.