Ulvan Polysaccharide of Ulva lactuca From Coastal Indonesia: Functional Prebiotic Properties via Enzymatic and...

Indonesia's rich macroalgal biodiversity offers valuable resources for functional food development, particularly ulvan, a sulfated polysaccharide derived from Ulva lactuca. While ulvan shows promising prebiotic potential, its extraction efficiency and structure-function relationships are strongly influenced by processing conditions. This study optimized ulvan recovery from U. lactuca harvested from the Bolok coastal waters (Kupang, Indonesia) and evaluated its chemical composition, structural characteristics, and in vitro prebiotic functionality. Three extraction strategies were compared: mild hydrothermal-enzymatic (cellulase)-ultrasonication (HEU-C), mild hydrothermal-multienzyme-ultrasonication (HEU-Mix), and a nonenzymatic hydrothermal-ultrasonication (HU) method. The HEU-C method achieved the highest yield (29.85%), significantly exceeding that of HU (12.22%). Chemical analyses revealed that HEU-C extracts contained the highest levels of polysaccharides, reducing sugars, and uronic acids, whereas HU extracts retained the greatest sulfate content. FTIR and SEM analyses demonstrated that different extraction methods induced distinct structural modifications and changes in surface morphology. Ulvan extracted via HEU-C exhibited the strongest antioxidant activity (DPPH radical scavenging capacity: 50.58%), followed by HEU-Mix and HU. In vitro fermentation assays showed that HEU-C extracts (1%-5% w/v) significantly promoted the growth of Lactobacillus rhamnosus RAL43, Lactobacillus plantarum RAL25, and Lactococcus lactis SwR14, with performance comparable to or exceeding that of fructooligosaccharides. Fermentation was further characterized by soluble sugar consumption and the production of short-chain fatty acids (SCFAs), including acetic, propionic, and butyric acids. Overall, enzyme-assisted extraction enhanced ulvan bioactivity, structural accessibility, and prebiotic performance, positioning it as a promising functional ingredient for microbiota-targeted food applications and marine-derived nutraceutical development.