Shelf-life extension of squid and shrimp skewers through the application of edible solutions

Student thesis: Master's Thesis


Seafood are highly nutritious and indispensable to a healthy diet. Growing interests in healthy lifestyles result in increasing demands for innovation of seafood products leading to more accessible and less time-consuming confection products. However, seafood is also very perishable, and product degradation is a major cause for the large quantities of product waste, which is a matter of great concert for both the industry and the consumers. This degradation is, in part, consequence of the growth of specific spoilage organisms in the product. With the objective of increasing shelf-life of a seafood product (squid and shrimp “espetada”), this work focused on the development of natural treatments to inhibit the bacterial proliferation and spoilage throughout 5 days of product storage under refrigeration conditions. To achieve that, an initial microbiological characterization of the product was performed, and the antimicrobial activity of several natural compounds was evaluated against 100 microorganisms previously isolated from the fish samples. Identification of isolates resulted in the detection of several Enterobacteriaceae (Serratia spp., Klebsiella spp., Hafnia spp., Rahnella spp., etc.), Pseudomonas spp. and Lactic Acid Bacteria (Lactococcus spp., Leuconostoc spp. and Weissella spp.). Escherichia coli or Listeria monocytogenes were not found in each batch analyzed. Three selected natural compounds, Citrox®, Thyme essential oil and vinegar solutions, were applied through different techniques and their effects in bacteriological growth was analyzed in comparison with untreated samples from the same batch immediately after reception and after 2 and 5 days of refrigerated storage. Citrox® at 1% v/v (immersion) and 3% v/v (pulverization) as well as Thyme essential oil at 0.2% v/v (immersion) were not effective in retarding the growth of total viable organisms, Lactic Acid Bacteria, Pseudomonas spp. and Enterobacteriaceae. On the contrary, bacterial inhibition was observed for both immersion and pulverization of vinegar, with significant higher effect (P < 0.05) only after immersion for 5 minutes with reductions around 2 log cycles at the end of 5 days of storage. Although more experimental tests are required, this preliminary study demonstrated that natural compounds such as vinegar solutions could be used to prevent the bacterial growth and to prolong the shelf-life of such perishable squid and shrimp “espetadas”.
Date of Award23 Feb 2021
Original languageEnglish
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorJoana Inês Bastos Barbosa (Supervisor) & Paula Teixeira (Supervisor)


  • Antimicrobial activity
  • Natural compounds
  • Preservation
  • Vinegar


  • Mestrado em Biotecnologia e Inovação

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