REPOSITORY > RESULTS

Abstract

A reduction in agricultural productivity associated with water scarcity and land
degradation, combined with the growing world population and malnutrition highlights the
need for new alternative food sources. In this challenging field, Spirulina microalgae
emerges as a promising candidate thanks to its high nutritional value and beneficial effect
on human health. Unlike conventional foods, Spirulina also offers a more sustainable means
of production. However, despite its potential, alternative products like Spirulina often suffer
from a lack of quality and safety inspection, leading to fluctuations in their overall quality.
This thesis focuses on determining the quality safety and authenticity of Spirulina
products from the Slovenian market In addition, the lactic acid fermentation of Spirulina
biomass, considering its potential to improve the nutraceutical profile, is also investigated,
as is the subsequent extraction of bioactive compounds using various solvents. The role of
Spirulina biomass fe rmentation and the difference in antioxidant activity between water
and ethanol extracts are investigated at the cellular and proteome level using yeast as a
model organism. The Spirulina ethanol extracts are then further assessed at the molecular
level (proteins, to explore the role of lactic acid fermentation in compound
transformation.
The first part of this doctoral thesis focuses on the quality and safety of commercial
Spirulina based dietary supplements in Slovenia. It involves investigating their amino acid,
fatty acid and elemental composition and provides information on compliance with the
declared nutrient values. In addition, an assessment of iron bioavailability in Spirulina
products is presented. The findings confirm that Spirulina supplements are a valuable
source of essential and non-essential amino acids and ω 6 but not ω 3 polyunsaturated
fatty acids. They are also a rich dietary source of phosphorous (3.36-26.70% RDA), calcium
(0.15-29.50% RDA), selenium (0.01-38.60% RDA) and potassium 0.50-7.69% RDA).
However, an analysis of iron bioavailability suggests that despite their high iron content
(7.64-316.00% of RDA), only a small fraction (8.00-18.00%) is bioavailable. Moreover, the
addition of additives to Spirulina products leads to significant variations in nutrient
content and lower product quality. Additionally, inappropriate declarations were found in
86.70% of analyzed samples.
The second part of the thesis focuses on studying the impact of lactic acid fermentation
on Spirulina biomass and the choice of solvent on the antioxidant properties of the final
extract. The fermentation process was carried out using L actobacillus plantarum bacterial
culture. The study presents the nutritional composition of the biomass (including minerals,
proteins, fats, carbohydrates and dietary fibers) before and after fermentation.
Additionally, it provides the total phenolic content and in vitro antioxidant activity of
water and ethanol extracts from both non-fermented and fermented broth. The effect of
Spirulina treatment in vivo is demonstrated by cellular antioxidant activity and lipid
peroxidation, and cell response at a proteome level using the yeast Saccharomyces
cerevisiae. The results show how fermentation increases protein bioavailability while
reducing the fat content (from 6.26 before to 6.00% dwt after fermentation). Ethanol
extracts also exhibit higher in vitro (30.00% higher) and intracellular (20.00-40.00% higher)
antioxidant activity and lower intra cellular oxidative lipid damage (from 13.80 before to
5.71 fluorescence/optical density after treatment). Additionally, a greater antioxidant
efficiency of ethanol than water extracts and a lowering of cell stress response related
protein expression in yeast treated with fermented Spirulina ethanol extract is observed.
The following proteome analysis of the fermented Spirulina ethanol extracts showed a
decrease in protein content (from 847 to 490) after fermentation and consequent increase
in amino acid content indicating a proteolytic activity during fermentation. Similarly, the
lipid content decreased, while the lipid metabolites increased. The chlorophyll and
carotenoid content lowered after fermentation.
The final part of the thesis explores combining elemental composition and stable isotope
ratios to verify the country of origin of Spirulina and other algal products. This approach
is also employed to determine the potential presence of undeclared ingredients in
commercial products. The method successfully differentiated between Hawaiian, Italian
and Portuguese products (100%), as well as a good separation of Chinese samples. However,
the separation of Indian and Taiwanese samples (66.7%) was less successful.
To summarize, this thesis provides an insight into quality and safety of Spirulina
products from the Slovenian market, and shows that differences in isotopic, elemental and
nutrient composition reflect cultivation, processing methods and environmental conditions,
and combined, provide a promising tool for determining the quality and authenticity of
Spirulina and similar algal products Finally, the discovery of essential role of lactic acid
fermented Spirulina in combating cell oxidative stress and its implications in metabolomics
raises new questions offering new research possibilities.