Optimizing fermentation time to improve the safety and quality of a Portuguese-style fish sausage

Introduction: The growing demand for sustainable alternatives to traditional fermented sausages has stimulated the development of fish-based products. Since fish is highly perishable raw material, processing conditions must ensure microbiological safety while preserving product quality. Fermentation is a key step in achieving these objectives; however, information regarding the optimization of fermentation conditions for fish-based sausages remains limited. This study evaluated the effect of refrigerated fermentation time on the microbiological safety and physicochemical quality of a Portuguese-style fermented tuna sausage.

Methods: Experimental sausages were prepared using yellowfin tuna (Thunnus albacares) loin, fermented pepper, garlic paste, salt, monosodium glutamate, and sodium nitrite. Two refrigerated fermentation conditions were tested (24h and 36h at 4°C), followed by stuffing into vegetable casings, cold smoking, and dehydration until approximately 40% weight loss was achieved. Physicochemical parameters (pH and water activity, aw) and microbiological analyses follow ISO standards.

Results: Extending fermentation from 24h to 36h improved microbiological quality throughout processing. Enterobacteriaceae counts decreased by 0.8 log CFU/g after 36 h of fermentation compared with 0.4 log CFU/g after 24h, with final reductions of 2.1 and 1.2 log CFU/g, respectively. Lactic acid bacteria increased by 2.9 log CFU/g after 36 h of fermentation and by 3.5 log CFU/g in the final product, compared with increases of 2.5 and 2.9 log CFU/g under the 24h condition. Listeria spp., Clostridium perfringens, and Bacillus cereus remained below the detection limit (<50 CFU/g) throughout processing. Final products exhibited similar aw values (0.91), whereas pH was slightly lower after 36h of fermentation (5.78) than after 24h (5.87).

Conclusions: Extending refrigerated fermentation from 24h to 36h enhanced microbial stabilization, promoting greater growth of lactic acid bacteria and improved reduction of Enterobacteriaceae without adversely affecting physicochemical characteristics. These findings highlight fermentation time as a critical processing parameter to produce safe and high-quality fermented fish sausages.