On Mon, 31 Dec 2001, Freek Huskens wrote:
> Dear List members,
> Does anybody have experience with " light tables " for visually checking
> fresh Tilapia ( or any other fish fillets ) fillets for foreign material ?
> We have tried out bulbs up to 500 W with the light source below a glass
> table, but could not achieve good results in making the fillets translucent
> / foreign objects visible. Any ideas / input / experience would be most
> appreciated !
> Happy New Year to all !
>
> Freek
> Indonesia
Freek and Seafood Mailing List Subscribers,
FAO, FDA and Health Canada have published information on constructing a
candling table. Excerpts are below. For additional information, go the
the web address listed.
With warm holiday greetings to everyone,
Pamela Tom
University of California Sea Grant Extension Program
====================================================
Design and use of a candling table
The simplest kind of candling table is a box about 50 cm square with a
ground glass or perspex top about 6 mm thick. The inside of the box is
white, and is lit by two fluorescent tubes giving a white, not a coloured,
light. Electrical wiring should be installed by an electrician who
understands the wet conditions in which the box is to be used. The box
should be ventilated but splashproof.
To use the box, the fillet is laid down on the illuminated top; worms show
up as dark shadows in the flesh, and can be removed with forceps or a
knife. Light from above the box should be restricted; the box is useless
in bright sunlight for example. An experienced operator can handle up to
300 fillets an hour, but the eyes rapidly become fatigued and efficiency
falls during long spells, with the consequent risk of greater numbers of
worms passing undetected.
Source: The information in this note has been prepared jointly by the
Marine Laboratory of the Department of Agriculture and Fisheries for
Scotland and the Torry Research Station of the Ministry of Agriculture,
Fisheries and Food.
http://www.fao.org/wairdocs/tan/x5951e/x5951e01.htm
====================================================================
Equipment and materials
-Sharp knife
-Candling table. Rigid framework to hold light source below rigid working
surface of white, translucent acrylic plastic or other suitable material
with 45-60% translucency. Length and width of working surface should be
large enough to permit examination of entire fillet, e.g., 30 x 60 cm
sheet, 5-7 mm thick.
-Light source. "Cool white" with color temperature of 4200 K. At least two
20-watt fluorescent tubes are recommended. Tubes and their electrical
connections should be constructed to prevent overheating of light source.
Average light intensity above working surface should be 1500-1800 lux, as
measured 30 cm above center of acrylic sheet. Distribution of illumination
should be in ratio of 3:1:0.1, i.e., brightness directly above light
source should be 3 times greater than that of outer field, and brightness
of outer limit of visual field should be not more than 0.1 that of inner
field. Illumination in examining room should be low enough not to
interfere with detection of parasites, but not so dim as to cause
excessive eye fatigue.
Source: FDA's Bacteriological Analytical Manual Online, Ch. 19 "Parasitic
Animals in Foods."
http://vm.cfsan.fda.gov/~ebam/bam-19.html
Note: sample preparation is included plus a discussion on the ultraviolet
(UV) light procedure is for fish with dark flesh and for breading removed
from fish portions.
==============================================================================
Candling light table
The recommended light table for candling should have at least two 20 watt
"cool white" fluorescent tubes. The light source should be held by a
rigid framework below a white, translucent acrylic plastic or other
suitable material with a translucency of between 45-60%. This working
surface should be approximately 30 x 60 cm and 5-6 mm in thickness. The
average light intensity should be between 1500 and 1800 lux as measured 30
cm above the center of the acrylic sheet. Overhead illumination should be
at least 500 lux. Adequate results may also be obtained in the laboratory
using a simple photographic light table.
Candling works equally well with fresh or previously frozen fillets. The
efficiency of the candling technique is largely dependent upon the
thickness of the fillet being examined. Large, thick fillets, therefore,
may pose a particular problem due to the increased production costs and
loss of value involved with slicing such fillets. The candling technique
is generally considered to be a costly and inefficient means of detecting
and removing parasites from fillets. The technique is also limited in
that it cannot distinguish between live and dead parasites.
Source: "Isolation and Identification of anisakid roundworm larvae in
fish" by Brent Dixon, Bureau of Microbial Hazards, Health Canada September
1995.
http://www.hc-sc.gc.ca/food-aliment/english/publications/compendium/volume_4/exflp1.pdf
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