Linda Benedict, Ahmedna, Mohamed, Prinyawiwatkul, Witoon | 8/5/2009 12:17:55 AM
Viacheslav L. Sereda, Witoon Prinyawiwatkul, Mohamed Ahmedna, Ramu M. Rao, Alfred F. Trappey II and Douglas L. Park
Soft-shelled crawfish, often referred to as soft crawfish, have been consumed in Louisiana for many years. Commercial production of soft crawfish follows the annual molt cycle. Soft crawfish are produced by holding and feeding large numbers of the immature, hard (intermolt) crawfish in culture trays until they molt.
The quality of soft crawfish is critically affected by postmolting calcification and time. Calcium that initially hardens the soft exoskeleton is obtained from the dissolving gastroliths (calcium stones in the stomach), hepatopancreas (liver and pancreas), blood (so-called hemolymph), and water and food when feeding resumes. Shell hardening normally takes 72 hours. Crawfish should be harvested immediately after molting to ensure the best quality.
The longer the post-molting time, the more calcium is dissolved from gastroliths and deposited in the shell. As the new shell gets harder, the less marketable the crawfish becomes as a premium product. To obtain the best quality for consumption, soft crawfish must be collected within two to eight hours, depending on the water temperature. Ninety percent of crawfish molt during the midday hours (10 a.m. to 3 p.m.). If the newly molted crawfish are left overnight, some may harden to the point that they are not marketable as a premium product.
No research has been done to identify the allowable postmolting time that still yields consumer-acceptable fried soft crawfish. Increasing allowable post-molting time would enable producers to harvest more marketable soft crawfish. The objective of this study was to determine color and textural qualities and consumer acceptability of non-breaded fried soft crawfish as affected by post-molting calcification and time (6, 12, 18 and 24 hours).
Collection and sample preparation. For each different post-molting time of 6, 12, 18 and 24 hours, 70 crawfish were collected from the premolt tray and placed in separate molting trays for 6, 12, 18 and 24 hours, respectively. All crawfish were soaked in 1 percent salt solution for three hours at 42.8 degrees F and then placed in freezer bags. The bags were filled with tap water to cover all crawfish and stored at minus 4 degrees F. Ten hours before consumer sensory evaluation, all soft crawfish were thawed in the refrigerator and fried unbreaded in soybean oil at 350 degrees F for three minutes. Freshly fried crawfish were used for consumer sensory and physical property evaluation.
Color and texture measurements. Color measurements were determined using a spectrophotometer on the tail part of the fried soft crawfish. Colors were expressed as L* (brightness), +a* (redness), +b* (yellowness), hue angle (actual color) and chroma (intensity) values. Texture measurements were made on the third ring of the tail part and expressed as maximum force (Kg) required to shear an individual fried crawfish.
Consumer sensory evaluation. Fifty-eight consumers were randomly recruited from the Baton Rouge area. These consumers were between 18 and 65 years of age and not allergic to crawfish and soybean oil used for frying. One whole crispness of shell, overall texture and overall liking of four samples using a 9-point scale (1 = dislike extremely, 5 = neither dislike nor like, and 9 = like extremely). Consumers also classified each fried soft crawfish product as “acceptable” and “unacceptable” and indicated whether they would buy or not buy the product.
Results and discussion
Color. The purple, blue and red colors of live crawfish are attributed mainly to the carotenoid and carotenoprotein pigments. The carotenoproteins get denatured upon heating, causing the color changes from purple and blue to reddishorange. Color brightness (L*) and yellowness (b*) of fried soft crawfish generally increased with increased post-molting time (Table 1). Color redness (a*) was not drastically affected by post-molting time. The 24-hour fried soft crawfish had more intense orange color than did other samples as indicated by the hue angle and chroma values.
Texture. Maximum peak force (Kg) of fried soft crawfish decreased with increased post-molting time. The six-hour fried crawfish required more force to shear than did the 24-hour sample. This was likely due to the very elastic, thin layer of newly synthesized skin as opposed to the crispy, crushable shell of the 24-hour fried soft crawfish.
Product acceptability. Mean acceptability scores for appearance of fried soft crawfish were least influenced by postmolting time (Table 2). Color acceptability score of the 24-hour fried crawfish was less than that of the six-hour sample. Based on the color values (Table 1) and the sensory data (Table 2), consumers may prefer fried soft crawfish with darker red color over those with lighter orange color.
Texture quality of fried soft crawfish is critical to consumer acceptability. The shell crispness and overall texture of the 24-hour fried sample were as acceptable as the six-hour sample. This indicates that consumers may prefer fried crawfish with either a soft/elastic or crispy/crushable shell. Color, overall texture, shell crispness and, to a lesser extent, flavor and appearance, affected overall liking, but they did not cause the products to be unacceptable. Acceptability scores for appearance, flavor, shell crispness and texture of six- and 24-hour samples were slightly different. The 24-hour fried soft crawfish was as acceptable as the six-hour sample.
Purchase intent. The acceptability rating was highly related to the purchase intent rating. More than 82 percent of the consumers said the 24-hour fried soft crawfish were acceptable. More than 60 percent of consumers indicated the tendency to purchase this product if it were commercially available.
Changes in texture and color of fried soft crawfish were distinctively observed as a result of post-molting time and calcification, but these changes did not cause the products to be unacceptable. Comparisons of consumer acceptability scores for appearance, flavor, shell crispness, overall texture and overall liking of six-hour versus 24-hour post-molt fried crawfish showed no significant differences. Without exception, sensory acceptability scores for the 24-hour post-molt fried crawfish were equal to or higher than 6.0 (“slightly like” on a 9-point scale).
It is commonly believed that, to obtain the best quality for consumption, soft crawfish must be collected within two (at 80 degrees F) to eight (at 68-70 degrees F) hours after molting, depending on the water temperature. In this study, all crawfish were held in the trays at approximately 70-75 degrees F. Results from the consumer study showed that crawfish held for up to 24 hours after molting were still acceptable to consumers if served as a nonbreaded deep-fried product. Maximizing the harvesting time for soft crawfish would allow producers to harvest more marketable soft crawfish and thus perhaps increase revenue.
Viacheslav L. Sereda, Research Assistant; Witoon Prinyawiwatkul, Assistant Professor; Mohamed Ahmedna, Research Assistant; Ramu M. Rao, Professor; Alfred F. Trappey II, Instructor; and Douglas L. Park, Professor, all with the Department of Food Science, LSU Agricultural Center, Baton Rouge, La.
(This article was published in the summer 1999 issue of Louisiana Agriculture.)