From Cultivation to Commercialisation: The Stability, Degradation, and Interactions of Astaxanthin in Haematococcus lacustris Biomass

Abstract

This thesis investigated the stability of astaxanthin in Haematococcus lacustris biomass, from cultivation through the stages of downstream processing and storage, to its eventual product formulation. Astaxanthin is a valuable xanthophyll carotenoid and is widely considered one of the most powerful natural antioxidants. The freshwater microalga H. lacustris is regarded as the best source of natural astaxanthin and is the only source to have received direct approval for human consumption. H. lacustris is cultivated on an industrial scale to produce astaxanthin for the nutraceutical, pharmaceutical, and health-food industries, owing to its potent bioactive properties. Central to these applications is non-extracted astaxanthin in whole H. lacustris biomass, as this constitutes its own certified product, and is commonly used in nutraceutical dietary supplements or as an aquaculture feed ingredient. However, the instability of astaxanthin presents a significant challenge to its broader application. A crucial knowledge gap exists regarding the stability and degradation of non-extracted astaxanthin within H. lacustris whole biomass, as research has focused on astaxanthin from various biological sources after extraction or purification has been performed. This thesis investigates key aspects of H. lacustris cultivation, focusing on strategies to induce astaxanthin production, such as applying high light intensities, elevated temperatures, organic carbon supplementation, and nutrient deprivation. This was done during scale-up from lab- to pilot-scale in two 65L photobioreactors. Then focusing on the stability, degradation, and interactions of astaxanthin by investigating changes to the astaxanthin content of biomass and its functionality as an antioxidant under various biomass drying treatments, temperature regimes, and after the addition of additives. During H. lacustris cultivation, more extensive red phase induction strategies were found to increase astaxanthin accumulation, reaching up to 2.25% of cellular dry weight. H. lacustris biomass was dried using various techniques, with spray drying proving more effective than freeze drying, oven drying, and microwave drying for producing biomass suitable for storage. Long- and short-term storage of biomass at various temperatures demonstrated that optimal storage conditions are at -20°C, as even brief exposure to temperatures >20°C accelerates degradation. Additionally, nutraceutical additives with high antioxidant activity (e.g. mixed tocopherols, ascorbyl palmitate, lutein) stabilised astaxanthin, whereas metallic additives (e.g. copper, zinc, magnesium) promoted its degradation. This work provides insights into optimising processes to minimise astaxanthin degradation and extend its storage viability, offers practical recommendations to improve industry practices, thereby supporting the expansion of the natural astaxanthin industry.

Date of Award	25 Jun 2025
Original language	English
Awarding Institution	University of the Highlands and Islands