Investigating the Effects of Pre-treatments on the Functional Fermentation of Ulva spp. for Potential Novel Food Products

Abstract

Fermentation of Ulva spp., a protein-rich green macroalga, offers a sustainable approach for utilising an available resource and developing functional food ingredients. However, its high levels of inorganic matter, polyphenols, and complex polysaccharides such as ulvan pose challenges to microbial metabolism. This study investigated the effects of various pretreatment strategies, including hot water extraction and enzymatic hydrolysis, on the composition of Ulva spp, for fermentation with of Lactobacillus reuteri, and the fermentation of raw Ulva spp. with Fusarium venenatum.
Pretreatment methods and subsequent fermentations were evaluated for changes in reducing sugar, uronic acid, ash, and protein content over time. Hot water treatment for 20 minutes was the most effective condition, promoting moderate sugar release and relative protein enrichment while reducing mineral content. In contrast, extended heating (60 minutes) led to sugar degradation and decreased protein yields. Enzymatic degredation using ulvan lyase showed minimal effectiveness, likely due to residual inhibitors or enzyme instability.
Notably, bacterial fermentation trials showed an increase in reducing sugar levels, suggesting that the microbes survived but did not actively metabolise the released carbohydrates. This supports the hypothesis that inorganic matter and polyphenolic compounds, solubilised during pretreatment, may inhibit enzymatic and microbial activity. Fungal fermentation with F. venenatum led to an initial increase in protein content, peaking at 48–72 hours, before declining, indicating a limited fermentation window for optimal protein enhancement, but demonstrating promising potential for development as a mycoprotein ingredient.

Popular Abstract

From Seaweed Problem to Bioresource Potential - Can a coastal waste be transformed into a valuable ingredient and unlock its hidden potential?
Have you ever gone to the beach on a hot day, wanting to cool off in the water, only to find it saturated in a thick blanket of seaweed? This phenomenon is a direct result of eutrophication, a symptom of human impact on marine ecosystems, where nutrients from agriculture and wastewater enter the sea, creating the perfect conditions for algae and seaweed to thrive. Ulva is a common green seaweed found in coastal areas all around the globe. It is the primary suspect of these green tides. Removing these dense seaweed blooms is not only environmentally disruptive, but also expensive, with cleanup costs reaching up to $150 per tonne. However, instead of viewing Ulva as waste, what if we could turn this persistent seaweed into something useful? Efforts to valorise this abundant biomass from both the wild (green tides) and seaweed farming have economic, environmental and health benefits.
This degree project aimed at investigating the compositional changes to Ulva biomass through the application of a combination of two types of treatments, in order to enhance the fermentable component content. Ulva contains a unique polysaccharide called ulvan, a long-chain sugar molecule with sulphate groups that give it several beneficial biological properties. The first involved applying heat to extract ulvan from the biomass. The second used an enzyme called Ulvan Lyase. An enzyme is a biological catalyst, which speeds up a reaction and for this particular enzyme, it helps breaks down ulvan into its individual sugar components. These methods aimed to improve the availability of sugars that can be consumed as part of a fermentation with a common microorganism, used in probiotic foods which provides added benefits to the desired end product.
Ulvan has shown to have potential antiviral and anticancer effects, and Ulva also contains a compound known as polyphenols, which are known for their antioxidant and anti-inflammatory activities. These features make Ulva an exciting candidate for plant-based novel food products. However, these same characteristics also present a challenge. The complexity of ulvan, particularly its sulphated structure and the presence of polyphenols, makes the seaweed difficult to break down and ferment through enzyme and microbial inhibition. Fermentation is a crucial process in this project. It occurs when the microbes use the seaweed as a food source, and release by-products, such as lactic acid, to create a new product. This allows for increased availability of beneficial activities, microbes support gut health and improve the stability and longevity of the potential product.
Unlocking the full potential of Ulva proved more difficult than expected. Despite applying promising treatments, the seaweed’s complex biochemistry continued to resist efficient fermentation. As mentioned, Ulva’s dense polysaccharide structure and rich polyphenol content stood in the way, interfering with the conversion of its sugars into usable bio-products through acting like bodyguards, preventing the enzymes and microbes from getting to their victim. While this approach altered the composition of the biomass, changing its sugar profile, it didn’t result in a significant boost in fermentation performance. What became clear was just how complex Ulva is. Even with targeted breakdown methods, the seaweed’s polyphenols continued to disrupt the enzyme activity by stopping the enzyme from interacting with the large sugar molecules and fermentation process through inhibition. Removal of these compounds would potentially reduce inhibition, but these compounds are fundamental to what makes Ulva a great resource.
Yet, these challenges brought valuable insights. The treatments revealed how different strategies change Ulva’s biochemical makeup and pointed toward more refined processes that may one day unlock better yields. While the road ahead may require new enzymes or pre-treatment techniques, this study lays important groundwork for tapping into seaweed as a sustainable bioresource.
In short - Ulva is a tough nut to crack, but understanding its complexity is the first step toward unlocking its full potential.

• author: Fallon, Laura Anne
• supervisor: Roya R. R. Sardari
• organization: Biotechnology (M.Sc.Eng.); Biotechnology (MSc)
• course: KBTM01 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• keywords: Seaweed, Microbial Fermentation, Enzyme Degradation, Ulvan, Ulvan Lyase, Biotechnology
• language: English
• id: 9210442
• date added to LUP: 2025-08-25 08:21:44
• date last changed: 2025-08-25 08:21:44