Adding Value to Ready-to-eat Crustacean ProductProcess optimization for “entire” and “particulate”crustaceans using novel technologies

Abstract

The aim of the present study was to optimize and evaluate the potential of novel technological interventions in the production of ready-to-eat Irish edible crab (Cancer pagurus). The Thesis begins with a general overview of food preservation and main characteristics of edible crab including its significance for the Irish seafood industry. An initial study characterized the main microbiota present in raw and ready-to-eat brown crab and their thermal resistance. Results obtained showed the importance of Bacillus spp. and Staphylococcus spp. in these products. Characterisation of bacterial thermal resistance proved the effectiveness of recommended heat treatments to inactivate Listeria monocytogenes (F70°C7.5°C = 2 minutes). However, the study also revealed that the most severe heat treatment currently recommended, which has Clostridium botulinum non-proteolytic type E as a target microorganism (F90°C8.6°C = 57 minutes), is not sufficient to achieve a comparable inactivation (i.e. 6 Log10 cycles) of the most heat resistant bacterial spore isolated from crab samples namely, Bacillus weihenstephanensis. Following the microbial characterization studies, the potential for incorporating ultrasound to improve early stages in ready-to-eat crab production (i.e. the initial cooking step) was evaluated. The application of ultrasound during cooking enhanced the rate of heat transfer, allowing up to a 15% reduction in total cooking time. In addition, ultrasound also proved its efficacy for enhancing mass transfer from the crab to the cooking water. This improved crab cleaning during cooking would in turn allow the omission of the normal post cook cleaning process prior to packaging. Ultrasounds potential to enhance mass transfer from crab to the cooking water also prompted an investigation into its possible use to remove cadmium from crab. Results showed that ultrasound combined with mild temperatures has the capability to reduce the total cadmium content in edible crab by up to 22.8%. The results open the possibility for using ultrasound as alternative to resolve this issue for the crab industry. Following these studies the second heat treatment step (i.e. in-pack pasteurization) of ready-to-eat crab was optimized to minimize the impact of the treatment on the quality of the final product. Results showed that the colour of crab white meat was the parameter most affected by the heat treatment and therefore, a colour change kinetic for these heat induced changes was developed and used as a quality indicator for process optimization. Based on this study an optimal set of treatment conditions were proposed for the inactivation of C. botulinum non-proteolytic type E. However, based on the models developed the required heat treatment for a process which is solely thermal, would be too severe to retain a good quality. This situation would be further aggravated by the requirement for even more severe heat treatments if B. weihenstephanensis is considered as the target microorganism. Therefore, the use of alternative technologies (i.e. mano-sonication, mano-thermo-sonication and electron beam ionizing radiation) for the inactivation of the main bacterial spores isolated from brown crab was also evaluated. The use of ultrasound in combination with pressure and mild temperatures (i.e. Mano-Thermos-Sonication) showed a synergistic effect in terms of bacterial spore inactivation, which in turn would allow a reduction in the total processing time by over a 80% while still maintaining a similar level of inactivation to heat only. The use of irradiation also proved to be an effective technology to inactivate bacterial spores while still remaining below the limit of 10kGy established by WHO. In addition radiation was the technology least affected by changes in bacterial species or treatment media composition. Overall, the results of this thesis shows the potential for a number of alternative technologies and technical interventions to improve the processing of Irish edible crab and address present and future challenges in the production of these ready-to-eat products.