IR could boost flavour perception understanding

The technique could lead to a deeper understanding which parts of the brain respond to flavour and, in particular delicate flavour, which is restricted by current common techniques.

How consumers sense food is crucial knowledge for a food industry constantly organising the building blocks of new food formulations.

"The application of functional neuroimaging to the study of sensory evaluation (SE) on food attributes is a new area of research with much potential,"​ wrote lead author of the study, Masako Okamoto, from Japans National Food Research Institute.

Imaging of the brain's responses during food tasting is not a new technique and has been used extensively. However, the most common other techniques, namely positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and magnetoencephalography (MEG), have several technical limitations, argue the Japanese researchers behind the new study.

All three techniques, fMRI, PET and MEG, often require subjects to be lying down, which restricts movement and, say the researchers, allows only a limited volume of tastants to be presented.

"These limitations likely increase the taste threshold, and make it difficult to perform SE in the scanner, at least on samples with delicate flavours,"​ wrote the researchers in the journal Appetite​ (on-line ahead of print, doi: 10.1016/j.appet.2006.04.003).

So the researchers started looking at using functional near-infrared spectroscopy (fNIRS) to image the brain's responses to food and flavours.

The technique is said to be a non-invasive, optical method that monitors cerebral hemodynamics by measuring changes in the reduction of near-infrared light as it passes through tissue. The techniques is reported to be compact and less restrictive.

"Therefore, tasting conditions in fNIRS experiments can be much closer to those of normal sensory evaluation (i.e., tasting a mouthful of a sample in an upright position with little oral movement restriction),"​ said Okamoto.

To check if such a technique could be applicable to sensory evaluation (SE) of food attributes, 12 volunteers were recruited to taste tea samples. The volunteers were required to taste one tea sample and attentively memorise the flavours. They then rinsed their mouths for 10 seconds and tasted a second tea sample and were asked to judge if the teas were the same.

The experiment was regarded as an evaluation of 'memory-encoding'.

The results of this experiment were compared with a control experiment that required volunteers to taste similar tea samples but not to actively assess the flavours.

The fNIRS identified significant activation in the right and left lateral prefrontal cortex (LPFC) and in the right inferior gyrus, regions of the brain previously identified by other techniques as being involved in the cognitive processing of flavours and taste.

On the other hand, the experiment that required the volunteers to refrain from actively evaluating the tea samples there were no significant activations of these regions.

These data show that memory encoding of flavour does affect the response - an observation that has been reported before, but not previously demonstrated by a functional brain study, say the researchers.

Not only that, but the activity in both the right and left LPFC led the researchers to speculate that the hypothesis linking both perceptual and verbal encoding strategies for odor-difference tests, may also apply to flavour-difference tests.

The activation of the left LPFC areas and the ability of the volunteers to discern between the two tea samples shows that the technique of fNIRS is a viable tool for monitoring brain function during the sensory evaluation of intra-oral food attributes, wrote Okamoto.

"Further development and applications of the technique can be expected in the future,"​ he concluded.

Taste is a key driver in the €3.2 trillion global food industry and a greater understanding of the physiology of consumers, could lead to strong market advantages.