Mar Vall-Llosera Juanola, Livsmedelsvetenskap

Seaweed has been identified as a promising alternative food raw material to support the growing demand for sustainable and nutritious food products. The green species Ulva fenestrata is particularly promising based on its sensorial properties and nutritional value. However, rapid post-harvest deterioration limits its full potential for food use, calling for new stabilisation methods beyond conventional drying and freezing.

This thesis investigated how five different stabilisation strategies: osmotic dehydration driven by brining, microbial fermentation, high pressure processing (HPP), sous vide processing (SP) and antioxidant-aided drying, affect the microbial shelf life, colour, texture, volatile compounds, nutritional value and sensory profile of U. fenestrata, with the ultimate aim of diversifying the formats by which it can be used in food.

Concentrated brines containing 25% salt or 50% sugar reduced water activity from 0.98 to 0.80 or 0.89, respectively, and extended microbial shelf life from 13 to 48 or 78 days, respectively. HPP (600 MPa, 3min) outperformed SP (80 °C, 7 min) in terms of initial microbial inactivation, and gave ≥28 days shelf life. Fermentation with selected lactic acid bacteria (LAB) strains (Levilactobacillus brevis, Lactiplantibacillus plantarum and Lactiplantibacillus paraplantarum) increased in vitro-assessed protein digestibility and mineral accessibility. Among the wet-stabilization methods, colour and texture were best kept by concentrated salt brines and SP. However, following prolonged storage in concentrated brines, up to 70% proteins and 42% total fatty acids were lost, indicating a trade-off between microbial spoilage and nutrient retention. Drying at 60 °C better preserved colour than 40 °C, and combining the former with antioxidant rinsing was superior in maintaining seaweed-odour and limiting volatile compound development over 550 days of storage.

Overall, these findings demonstrated that all the evaluated stabilisation strategies, except for SP, can extend the shelf life of U. fenestrata by ≥28 days, but with different effects on sensorial and nutritional properties. The evaluated strategies, which were either new to seaweed as a whole (combined antioxidant treatment and drying, sugar-brining), new to U. fenestrata (salt-brining and LAB-fermentation) or having new settings (SP, HPP), increase the possibilities for high-quality seaweed to reach the food market, and diversify its available formats.