1. Introduction
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Louisiana USA has a thriving crawfish Procambarus clarkii and P. zonangulus production industry. During the 1997–1998 season, farm production from 44,500 ha
totaled 16.4 million kg, which was worth US22.5 million. The natural fishery of wild Ž
crawfish accounted for an additional US19 million Louisiana Cooperative Extension .
Service, 1998 . Farm-raised crawfish are also produced in other southern states of the US, albeit in much smaller quantities. The preferred way to prepare crawfish for the
consumer is to boil the whole animal in seasoned water. The consumer then extracts the abdominal meat by hand, which is also the preferred method for eating crawfish in
Europe — a major export market for Louisiana’s largest, most valuable crawfish. A portion of the annual harvest is also commercially processed for the abdominal meat
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. Huner et al., 1994 .
To render a more appealing product for the whole-crawfish market, crawfish are sometimes placed in depuration or ‘‘purging’’ systems for 1 or 2 days. In these systems,
crawfish are confined in water or very humid environments and food is withheld. This process cleans the exoskeleton of mud and debris, and eliminates or greatly reduces
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digesta in the hindgut intestine , which many consumers find unappealing. When the Ž
. exoskeleton is removed ‘‘peeled’’ from the abdomen, the hindgut, which lies dorsally
along the abdomen, is exposed. The full, dark colored intestine of an unpurged crawfish conspicuously contrasts with the light colored meat. The exposed contents of the full
intestine are particularly offensive if the intestinal wall is ruptured during peeling, contaminating the meat with fecal material. Purging mitigates this unappealing aspect of
crawfish consumption. The intestine of a fully purged crawfish is smaller, translucent, and much less conspicuous. Purging also serves to remove ingesta from the foregut and
clean the branchial chamber of grit and mud, which contaminate the cooking water when multiple batches of crawfish are boiled.
In the southern USA, many laypeople improperly define purging as placing crawfish in a tub of water with 400–500 g of sodium chloride for a few minutes. This does little
to remove the contents of the intestine and is simply little more than a cursory wash. The salt has little effect. Purging, to the extent that intestinal contents are significantly
reduced, requires additional time.
Some people, especially Louisianaians, who have been eating crawfish for many years, are accustomed to non-purged crawfish and do not find them objectionable;
nonetheless, many would probably prefer a purged product if the higher costs were reasonable. Although the current market for purged crawfish is relatively small due to
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lack of public awareness and price differences 15–25 higher , purging has contributed Ž
to repeat sales and loyalty to certain producers or distributors Haby and Younger, 1989; .
Avery and Lorio, 1996 . Promotions of purged crawfish in non-traditional locales have helped to foster new markets. At one time, purging was also thought to increase shelf
Ž life of crawfish held in a cooler until cooking Haby and Younger, 1989; Huner and
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. Barr, 1991 , but this claim has been refuted McClain, 1994 . However, purging may
benefit other aspects of crawfish processing, such as lower bacterial counts in peeled Ž
. abdominal meat Treece, 1984 .
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Huner et al. 1994 review some of the commercial depuration systems that can be Ž
. classified as either immersion types crawfish are totally immersed in water or spray
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types non-inundated crawfish exposed to water spray or mist . Few studies have
Ž evaluated the purging process
Lawson and Drapcho, 1989; Lawson et al., 1990; .
McClain, 1994; McClain et al., 1994 , and the scope and findings of those studies were limited. Many aspects of crawfish depuration remain undocumented. This study was
conducted to evaluate several aspects of the purging process. The main objectives were to examine the efficiency at which crawfish evacuate the contents of the hindgut under
‘‘typical’’ purging conditions and to compare mortality and the efficiency of gut evacuation in two types of depuration systems at a common loading rate. Evacuation
efficiency was examined at 12-h intervals, in lieu of 24-h intervals commonly used in the industry, to obtain more accurate assessments of gut evacuation rate.
2. Materials and methods
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