Supervisor:
Mette Hedegaard Thomsen

Co-Supervisor:
Tanmay Chaturvedi

Assessment Committee:
Mette Lübeck(Chair)
Andriy Luzhetsky, Pharmaceutical Biotechnology, Saarland University, Germany

Robert Baldwin, NREL, 

 

Moderator:
Mette Lübeck

Abstract:

As a part of the response to challenges related to climate change, it is necessary to transition from fossil-based linear economies towards circular bioeconomies. This requires the development of technologies to use the world’s biomass resources efficiently, minimising waste production. However, another challenge, soil and water salinisation, is also becoming more prevalent worldwide. Indeed, we are required to enhance the use of biomass, and, at the same time, soils are becoming toxic for the majority of plants to sustain their growth and accessible freshwater resources are depleting. This is happening at an increasing rate due to salinisation and the higher occurrence of droughts and heat waves. Only approximately 1 % of the world’s known flora are halophytes, naturally salt-tolerant plants that thrive in saline environments, and harnessing these plants for agricultural use has been suggested as one of the key implementations to face the upcoming challenges.

 

In this explorative PhD project, halophyte species suggested for biosaline agriculture, namely, Crithmum maritimum, Salicornia europaea, Salicornia ramosissima, and Tripolium pannonicum, were evaluated for their potential towards green biorefinery applications. In green biorefineries, which have been developed to produce feed protein from grass biomass and agro-residues, biomass is fractionated into green juice and fibres, and these fractions are processed separately. In this project, the effect of the cultivation salinity on the fractionation performance and distribution of primary metabolites in halophytes was assessed, and significant effects were observed.

 

After fractionation with a screw press, the protein precipitation from saline halophyte green juice was investigated using methods established for forage-based green biorefineries: heat coagulation, acidification, and lactic acid fermentation. Afterwards, the production of protein-enriched concentrate by lactic acid fermentation of S. ramosissima juice with probiotic bacterial strain was studied further in a bioreactor setting. The use of halophytes for the production of functional animal feed supplements could help to diversify the source of protein and decrease the dependency on imported feed by providing a local source, especially in the arid and semi-arid regions, where the cultivation of forages and crops is limited.

 

Halophytes produce high concentrations of bioactive secondary metabolites as their response to environmental stress, such as high salinity, UV radiation, extreme temperatures, drought, and waterlogging. These compounds, also known as phytochemicals, have various biological activities and health benefits, which have made them interesting for biopharmaceuticals, nutraceuticals, food additives, and cosmetic applications. Therefore, bioactive compounds found in halophytes were reviewed.  Phytochemicals can be extracted from the fibre residue, and the extracts obtained from the screw-pressed halophyte fibres were analysed for their content of phenolic compounds using different absorption spectroscopy assays and chromatographic methods. Bioprospecting towards high-value bioproducts was done by analysing the extract for their in vitro antioxidant properties, cytotoxicity, and inhibition activity towards enzymes linked to neurodegenerative diseases, metabolic diseases, and hyperpigmentation. Targeting products for these sectors can improve integrated biorefinery economics, provide maximum feedstock valorisation in a cascading process, and contribute towards a sustainable circular bioeconomy.

 

Extractives-free halophyte biomass, consisting of relatively pure lignocellulose, was subject to hydrothermal pretreatment and enzymatic hydrolysis. The enzymatic convertibility was tested in order to estimate the pretreatment severity needed to break the lignocellulosic structure for potential biochemical or bioenergy production. 

 

Overall, this PhD project provided a comprehensive general view of the potential processes and target products of halophyte-based green biorefinery, and the results can be used as a basis for further investigations. The interdisciplinary project also contributes to closing the gap between process engineering and other related scientific disciplines, which must be done to develop efficient and meaningful biomass processing systems and bring the green transition forward.