VFA analysis wont give you anything, you need to detect Esters, aromatic compounds, terpenes as they are responsible for fruity smell.  But if bacteria are not grow using fucose, something must be hapening ie utilization or fermentation

The above response is likely correct.

It could be due to a metabolic byproduct produced by default under anaerobic conditions, a metabolic product produced by fucose as a trigger or simply a degradation byproduct of the fucose.

In the later case, you can check the KEGG pathways for the fucose:

http://www.genome.jp/dbget-bin/www_bget?cpd:C01019

Or even try the biodegradation prediction, although I'm not completely sure it would be adequate for this compound, the products may give you some ideas where to look for:

http://eawag-bbd.ethz.ch/predict/notbepredicted.html

Awesome.  Thank you all very much for the responses.  I've got a few ideas on how to proceed . I'm trying some extended incubations in media that contains fucose to try and get as much of this smell as possible.  I think I'll have my adviser smell the cultures herself to make sure I'm not just imagining things.

Thanks again!

Have you published your work already?, I study fucosylated compunds and got interested in your topic.