Novel technologies for shell loosening and meat quality of shrimp (Pandalus borealis)

Research output: Book/ReportPh.D. thesisResearch

  • Thi Tem Dang
The shrimp industry is challenged by the peeling of cold-water shrimp (Pandalus borealis) due to the tight muscle-shell connection. Therefore, the shrimp manufacturers traditionally mature the shrimp on ice or in brine for up to 4-5 days in order to loosen the shell from the meat before peeling. However, since shrimp is quickly perishable, such a long maturation, even at low temperature, may degrade the quality and increase the microbial risk of the shrimp product. Novel methods are, therefore, in demand to loosen the shell from the meat without compromising the meat quality. The present thesis presents the investigation of the effects of four technologies (enzyme, ultrasound, high pressure, and ohmic heating) on shrimp shell-loosening (measured as peelability) and on quality, and the corresponding mechanisms. Firstly, to assess the impact of the technologies a new standardized, quantitative method to measure peelability was developed. The work for pulling off the shell was measured and normalized ensuring a self-consistent method independent of shrimp size. It was shown that the peeling work is the main attribute of peelability, and lower peeling work corresponds to easier peeling. In addition, the proportion of completely peeled and incompletely peeled shrimp and meat yield were obtained to give the full peelability profile. Enzyme (20 h) was found to be the most effective shell-loosening technology in terms of peeling work. The best peeling was obtained with a combination of an endoprotease and an exoprotease (0.25% Endocut 03L and 0.25% Exocut A0) for 20 h resulting in 100% completely peeled shrimp, 3 mJ/g, and 89% meat yield. Enzyme concentration and maturation duration were more influential on the peelability than pH. It was further found that the enzyme solution was reusable for a second maturation, since 95% of its activity was maintained and reduced the peelability by only 10% compared to the first cycle. The enzyme-induced shell-loosening was suggested (microscopic and proteomic techniques) to be caused by the intense degradation of structural proteins resulting in loss of structural materials from the muscle-shell attachment. Additionally, the enzyme-matured shrimp meat were more red, firmer, resilient and chewier than the industrial reference shrimp. Simultaneous ultrasound-enzyme treatment (3-4 h, ≤5°C) was the second best shell-loosening approach and was more effective than the individual treatments (ultrasound alone 3-4 h and enzyme alone 3-4 h) in terms of peeling work (4 mJ/g). The cavitation bubbles generated from ultrasound pit (microscopic and IR techniques) the layers of the shell, generating pathways for enzyme diffusion into the muscle-shell attachment and subsequent enzymatic hydrolysis of the structural proteins. Temperature control during ultrasound was found essential to avoid detrimental effects on the shrimp quality, thus low temperature (≤5°C) was recommended. The quality of simultaneous ultrasound-enzyme treated shrimp was similar to the raw shrimp, but more red, firmer, resilient, and chewier than the industrial shrimp. High pressure was less effective in facilitating shrimp peeling and, generally, increasing pressure level and time increased the peeling work, while temperature had insignificant influence. Pressurization at 100 MPa for 3 min at 5°C resulted in the lowest predicted peeling work (6.6 mJ/g) based on a response surface methodology experimental design. It was found that the mechanisms of shell-loosening and shell-tightening depended on the pressure level. The mechanism (microscopic and proteomic techniques) governing the easier peeling (shell-loosening) at mild condition (100 MPa) was the breakdown of high molecular weight proteins in shell and epidermis followed by some loss of the resulting peptides, in effect disrupting the muscle-shell attachment. However, the HP treatment also caused stabilization of collagen, thus hindering the shell-loosening process to some extent. Contrary, the mechanism underlying difficult peeling (shell-tightening) at higher pressure (600 MPa) was attributed to more effective structural stabilization of collagen by hydrogen bonds and crosslinks. Shrimp meat treated with high pressure at 600 MPa were partly denatured (myosin) and less red (astaxanthin loss). Ohmic heating generally showed insignificant effect on shrimp peelability when it was used as a pre-treatment followed by salt maturation. Noticeably, the peeling work obtained at high temperature (e.g. 50°C) was markedly higher than the salt-matured control, indicating a shelltightening effect. At high temperature the collagen in shell and epidermis is denatured (45°C for shell and 55°C for epidermis) resulting in disruption of the triple-helical structure into random coils that reassembles into a gel matrix upon following cooling. This gel tightly adheres the shell to the meat, causing a tightened muscle-shell connection. Shrimp meat treated with ohmic heating at 50°C were denatured and less red (astaxanthin loss). In conclusion, enzyme, ultrasound, and high pressure are promising technologies, but at varying degree of efficiency in facilitating shrimp peeling, whereas ohmic heating as a pre-treatment was less effective.
Original languageEnglish
PublisherDepartment of Food Science, Faculty of Science, University of Copenhagen
Publication statusPublished - 2018

ID: 214871343