Characterization of weakened haematococcus pluvialis encapsulated in alginate-based hydrogel

Authors: ONINKU, BECKHAM - Delaware State University; LOMAS, MICHAEL - Bigelow Laboratory For Ocean Sciences; Burr, Gary; ARYEE, ALBERTA - Delaware State University

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2025
Publication Date: 4/11/2025
Citation: Oninku, B., Lomas, M., Burr, G.S., Aryee, A.N. 2025. Characterization of weakened haematococcus pluvialis encapsulated in alginate-based hydrogel. Journal of the Science of Food and Agriculture. https://doi.org/10.1002/jsfa.14273.
DOI: https://doi.org/10.1002/jsfa.14273

Interpretive Summary: Haematococcus pluvialis (Hp) is a chlorophyte microalga that has garnered significant attention for its high weight fraction of natural pigments, particularly astaxanthin (ASX), a powerful antioxidant with various health benefits. ASX is currently being investigated as a potential compound for producing functional foods and supplements with improved health benefits, such as anti-inflammatory and anti-cancer properties. However, its applications in food and nutraceuticals are hampered by its natural susceptibility to degradation caused by high temperature, oxygen, light and pH extremes. To overcome these limitations, various encapsulation techniques, including emulsification, freeze-drying, ionic gelation and extrusion, have been explored to increase the stability of ASX. Specifically, ionic gelation is a promising method for microencapsulating substances containing ASX, offering high encapsulation efficiency, the use of generally recognized as safe (i.e. GRAS) hydrogel materials and low operating temperatures that minimize carotenoid degradation. The encapsulation matrix's composition and structure significantly impact its protective capabilities and must have suitable storage properties. Alginate (ALG), an anionic polymer derived from brown macroalgae, has been widely utilized in food production as a result of its extensive availability, adaptability, non-toxicity and gelled matrix made of biocompatible materials. ALG is made up of repeating '-L-guluronic acid and 'Dmannuronic acid residues joined by 1,4 linkages. This polymer has shown high encapsulation efficiency in previous studies; for example, observed an approximately 100% encapsulation efficiency for lycopene-rich watermelon concentrate encapsulated in calcium ALG hydrogels, whereas another study reported a 93% encapsulation efficiency for palm oil encapsulated in calcium ALG hydrogels.

Technical Abstract: BACKGROUND: Haematococcus pluvialis (Hp), a freshwater chlorophyte microalga, is a major natural source of astaxanthin (ASX), a potent antioxidant with anti-inflammatory, anticarcinogenic and muscle pigmentation properties. However, ASX bioavailability is limited by the rigid cyst wall and, although cell wall rupture improves bioavailability, the free form is unstable under high temperatures, pH extremes, light or oxygen. Encapsulation techniques improve ASX stability, making it suitable for functional foods and aquaculture, especially in salmonid feeds where natural pigments are preferred. The present study evaluates the stability of weakened Hp (Hpw) biomass encapsulated in alginate (ALG) via ionic gelation. RESULTS: Encapsulation utilizing ALG achieved high efficiency (97 ± 2.63%) and loading capacity (32 ± 0.90%), confirming its suitability as a wall material. ALG-Hpw hydrogels displayed significant color intensity, enhancing potential feed or food hues. Low bulk density (0.59 ± 0.01 g cm-3 ), moisture content (11.97 ± 0.20%) and water activity (0.28 ± 0.00) suggest minimized oxidation processes. Hydrogels measured 1.30 ± 0.06 mm with a uniform sphericity factor of 0.058 ± 0.03. Confocal laser scanning microscopy confirmed uniform Hpw distribution and scanning electron microscopy revealed fissure-free surfaces, ensuring minimal permeability. DPPH (i.e. 2,2-diphenyl-1-picrylhydrazyl) scavenging activity was similar between Hpw extract (38.32 ± 2.30% to 96.32 ± 0.88%) and ALG- Hpw hydrogels (33.20 ± 1.55% to 93.30 ± 0.44%). ALG Increased Hpw decomposition temperature by 40.97 °C. Encapsulation of Hpw in ALG significantly enhanced the bioaccessibility of ASX. The ALG-based encapsulation effectively preserved ASX stability, retaining over 90% of its content under storage conditions. CONCLUSION: ALG is a suitable biopolymer for encapsulating Hpw, preserving antioxidant activity, and enhancing thermal properties, making it valuable for broader applications. © 2025 Society of Chemical Industry.