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579.6 --- 579.6 Applied microbiology --- Applied microbiology

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Since the beginning of the new millennium, research efforts as well as commercial activities concerning mass cultivation and applications of microalgae have gained momentum. The main current and future applications of microalgae are situated in four fields, i.e. biofuel production, wastewater treatment, aquaculture and high-value products. Antioxidants are a commercially important class of high-value products that could be obtained from microalgae. Antioxidants are omnipresent with applications in food and feed industry, cosmetics as well as in the chemical industry. The main objective of this PhD study was therefore to evaluate the potential of microalgae as a source of antioxidants, in view of future applications in food products, and to learn more about the different metabolites that contribute to the antioxidant activity of these unicellular photosynthetic organisms.From our results, it can be concluded that microalgae contain relatively high amounts of antioxidants and are therefore an appealing alternative to higher plants for the production of natural antioxidant preparations. Although microalgae are well known for their high carotenoid content, other components are important as well in relation to the antioxidant activity. In some microalgal extracts, the presence of pigments can interfere with evaluation of antioxidant activity by traditional assays that are based on spectrophotometric measurements. Therefore, the use of voltammetry as an alternative methodology for measuring antioxidant activity was investigated. Antioxidant measurement by square wave voltammetry correlated well with other established antioxidant assays and proved to be a reliable method to assess antioxidant activity in complex matrices. It was further found that antioxidant activity of microalgae highly depends on nutrient availability and growth stage. It was obvious that cultivating under nutrient limitation, especially when nitrogen is limited, leads to biomass that is poor in antioxidant activity. Although phenolic content and carotenoid content were significantly lower in biomass from nutrient deficient cultures, production of the antioxidant vitamins C and E was enhanced under nutrient limited conditions, particularly when phosphorus was the limiting nutrient. The fact that vitamins C and E contents increased upon nutrient stress while total antioxidant activity decreased suggests that the contribution of these vitamins to total antioxidant activity of the biomass is relatively little.Interestingly, microalgae do contain significant amounts of phenolics, comparable to those of carotenoids. A minor part (ppb levels) of the phenolics appear to be flavonoids, a class of polyphenols that until recently was believed to be totally absent in microalgae. In this PhD, the presence of recognized key intermediates of flavonoid biosynthesis (chalcones, dihydrochalcones, and dihydroflavonols) was demonstrated for the first time in microalgae, which points to the existence in microalgae of a plant-like flavonoid biosynthetic pathway and raises the fundamental question on the ancestral physiological function of flavonoids.

Academic collection --- 579.6 --- Applied microbiology --- Theses --- 579.6 Applied microbiology

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Microbial toxins. --- 579.6 --- Microbial toxins --- Toxins --- 579.6 Applied microbiology --- Applied microbiology

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Microbiologie --- Microbiology --- Microbiology. --- 57 --- 579.6 --- Infectious Disease Medicine --- Biological sciences in general --- Applied microbiology --- Periodicals --- 579.6 Applied microbiology

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Bacterial toxins --- 579.6 --- 615 --- 579.6 Applied microbiology --- Applied microbiology --- Bacterial antigens --- Microbial toxins --- Pharmacology. Therapeutics. Toxicology --- Bacterial proteins