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    Aroma characterization of five microalgae species using solid-phase microextraction and gas chromatography-mass spectrometry/olfactometry
    (Elsevier Sci Ltd, 2018) Hosoglu, Muge Isleten
    In this study, aroma compounds produced by three marine microalgae species (Crypthecodinium cohnii, Schizochytrium limacinum and Tetraselmis chuii) and two fresh water microalgae (Chlorella vulgaris and Chlorella protothecoides) important for nutritional applications were identified by means of solid-phase microextraction followed by gas chromatography-mass spectrometry (GC-MS), GC-olfactometry (GCO) and a sensory panel. Principal components analysis (PCA) was applied to the instrumental and sensory analysis data to visualize differences between the samples in terms of descriptive attributes and volatile compounds. Accordingly, C. cohnii was characterised by a high level of sulfur compounds (dimethyl sulfide, ethanethiol), and ester and alcohol compounds associated with distinct 'sulfur-cabbage', 'fruity', 'rosy', and 'boiled potato' aroma notes. While S. limacinum was characterised more by aldehydes and alcohol compounds associated with 'mushroom', 'cucumber', and 'fatty-grassy' aroma characteristics, the other three samples showed relatively higher levels of ketone and terpene compounds with 'woody' and 'cereal-like' sensory characteristics.
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    Fermented Spirulina products with Saccharomyces and non- Saccharomyces yeasts: Special reference to their microbial, physico-chemical and sensory characterizations
    (Elsevier, 2022) Sahin, Busra; Hosoglu, Muge Isleten; Guneser, Onur; Karagul-Yuceer, Yonca
    Innovative products produced from various sources through fermentation processes have been a resurgence of interest. This study was designed to determine the performance of fermented Spirulina (FS) products by three different yeast species including Debaryomyces hansenii, Kluyveromyces marxianus and Saccharomyces cerevisiae and investigate the microbial, physicochemical and sensory characteristics of products. The results showed that the increase in yeast cell number was around 3 log after 48 h fermentation in Spirulina medium without additional carbon source. Protein bands with a molecular weight of-51 kDa seemed less visible and bands 14-22 kDa disappeared after 48 h fermentation by K. marxianus showed strong hydrolysis of proteins during fermentation. The amino acid compositions of the three kinds of FS were different also compared to unfermented Spirulina (unFS). Glutamic acid, methionine, lysine, isoleucine and valine became more dominant in FS samples. According to GC-MS analysis, there was a decrease in the concentration of pyrazine, ketone and aldehyde compounds of FS compared to unFS. The flavor notes of seaweed, cardboard, earthy/muddy and cereal/ straw were found to be the highest in unFS than in FS detected by panelists during sensory evaluations. FS by K. marxianus is highly characterized as having the lowest seaweed and umami flavor attributes and higher fermented and rose attributes. Finally, the current study revealed that the potential of Spirulina biomass to be a suitable substrate for yeasts and fermentation of Spirulina with different yeast species led to different kinds of products.
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    Optimizing bioreactor conditions for Spirulina fermentation by Lactobacillus helveticus and Kluyveromyces marxianus: Impact on chemical & bioactive properties
    (Elsevier Sci Ltd, 2024) Yay, Cansu; Cinar, Zeynep Ozlem; Donmez, Serhat; Tumer, Tugba Boyunegmez; Guneser, Onur; Hosoglu, Muge Isleten
    This study focused on optimizing the production of fermented Spirulina (FS) products using a bioactivity-guided strategy with Lactobacillus helveticus B-4526 and Kluyveromyces marxianus Y-329 in a 3-L bioreactor. Various operating conditions, including aeration rates and pH modes, were tested. While both microorganisms thrived under all conditions, the cascade mode, controlling dissolved oxygen, enhanced protein hydrolysis and antioxidant activity, as confirmed by SDS-PAGE and DPPH/TEAC assays, respectively. Screening revealed that cascade FS significantly decreased viability of colon cancer cells (HT-29) in a dose-dependent manner, with up to a 72 % reduction. Doses <= 500 mu g mL- 1 of cascade FS proved safe and effective in suppressing NO release without compromising cellular viability. Additionally, cascade FS exhibited diverse volatile organic compounds and reducing the characteristic seaweed aroma. These findings highlight cascade FS as a promising alternative food source with improved bioactive properties, urging further exploration of its bioactive compounds, particularly bioactive peptides.