Dear Francisco, and others
You ask if assessing by taste 20 samples of shrimp in a day is likely to
result in a loss of 'sensitivity'. In my experience of sensory evaluation of
fishery products, quite considerable, I would answer no, but with one or two
reservations. I recall visiting a fish factory and speaking to the leader of
the quality control team who told me that the quality controllers might
taste up to 100 samples in a 7-hour shift. The company relied very heavily
on sensory evaluation of raw and cooked samples for quality assurance for a
demanding customer. In my laboratory, where I ran all of the sensory panels,
it was customary to evaluate by taste up to 12 samples in a session and up
to 3 sessions a day at busy times. We maintained statistical monitoring of
performance and there was no suggestion that performance was affected by
work load. Evaluation of 20 cooked samples for flavour/taste in a day is not
many for an experienced assessor.
The reservations relate to what is being evaluated and for what, and the
experience and motivation of the assessor. There are a few compounds in fish
which might affect odour receptors such as to reduce sensitivity. By this I
mean exposure to the compound will result in the lowered perception of the
intensity of the odour in subsequent evaluations of similar products -
adaptation in the sensory jargon. One such compound, for example, is
cis-4-heptenal which is the characteristic odour of cold-stored non-fatty
fish. There is one report, (Bett, K.L. & Johnsen, P.B., 1996. Challenges of
evaluating sensory attributes in the presence of off-flavours ( geosmin and
2-methylisoborneol ). Journal of Sensory Studies, 11, 1-17), that
methylisoborneol (MIB), one of the compounds responsible for earthy/musty
flavours in freshwater fish and crustacea induces adaptation in assessors,
but I conducted a comprehensive review of sensory properties of these
compounds about a year ago and this was the only reference to adaptation by
these chemicals I came across. I haven't conducted any systematic evaluation
of MIB to confirm this myself. If it is suspected that a chemical causes
adaptation, (and it is not easy to demonstrate the effect), then I would
recommend a slow pace of evaluation and the use of a palate cleanser such as
a plain unsweetened biscuit, (cracker), between samples. (I don't consider
palate cleansers are required for routine evaluation of fishery products
other than rancid products). Some flavours, for example rancid flavours of
fatty fish, can persist in the mouth and might confuse assessment of a
subsequent sample, but this is not the same as adaptation.
Another reservation concerns the experience and motivation of the assessor.
Very few people can not be trained to be good assessors for evaluating
sensory properties of fishery products. Over very many years of training and
selection of would-be assessors I have rarely had to reject a candidate
because he or she could not do the job. Usually the reason for rejecting a
candidate was because the person was unwilling to do the job. It is very
easy to get yourself off a sensory panel - just give erratic assessments. If
an assessor seems to be becoming less precise, or less accurate - these are
not the same thing - during the day I would first suspect boredom rather
than loss of sensitivity. If a person's job requires that the person
evaluates sensory properties of the products, then that can be a powerful
motivating factor.
Peter Howgate
----- Original Message -----
From: "Francisco Camino" <frankcamino@yahoo.com>
To: <seafood@ucdavis.edu>
Sent: Friday, May 21, 2004 7:49 PM
Subject: Oragnoleptical testing in shrimps
Dear Colleagues:
Some sensorial specialists can tell me if a technician
that make sensorial testing in shrimps, can loss
sensibility for correct sensorial testings,
considering that he or she does about 20 testings per
day. Please consider also that he or she tastes
samples of different origin (samples from low salinity
and presence of cianophytas, samples with mud taste,
samples with characterict taste, samples from high
salinity, etc.).
Please I would receive your comments.
Best regards,
Francisco Camino
Expack Seafood, Inc.
Brazil
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