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    Chemical, microbial, and volatile compounds of water kefir beverages made from chickpea, almond, and rice extracts
    (Springer, 2024) Ustaoglu-Gencgonul, Mutlu; Gokirmakli, Caglar; Ucgul, Bilgenur; Karagul-Yuceer, Yonca; Guzel-Seydim, Zeynep B.
    This study aims to assess the microbial, nutritional, volatile, and sensory characteristics of rice, almond, and chickpea water kefir beverages during refrigerated storage. Plant-based kefirs contained significant amounts of lactic acid bacteria and yeasts. The microbial content of kefirs was stable during 14-day refrigerated storage. Lactic acid, acetic acid, and tartaric acid are commonly detected organic acids in kefir samples. Almond and chickpea kefirs were rich in potassium mineral. Almond kefir had the highest ethanol content among plant-based kefirs, followed by chickpea and rice-based kefirs. Ethyl acetate, acetic acid, propionic acid, hexanoic acid, and benzenemethanol were identified as key volatile compounds in almond kefir and chickpea kefir samples using a GC-MS detector during water kefir fermentation. According to sensory analysis results, significant differences are present for all test parameters except odor. Almond kefir was the most accepted, while the other two kefir samples were below the general acceptance level (P < 0.05).
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    Effects of functional dairy based proteins on nonfat yogurt quality
    (Wiley-Hindawi, 2008) Isleten, Muge; Karagul-Yuceer, Yonca
    Production of nonfat yogurt demands a careful control of quality parameters. It is common to use skim milk powder (SMP) to increase the total solid content of nonfat yogurt, but some functional dairy-based proteins, such as casein/caseinates and whey proteins, may improve the quality of nonfat yogurt. The objectives of this study were to use whey protein isolate (WPI), sodium caseinate (NaCn) and yogurt texture improver (TI) in nonfat yogurt manufacture as an alternative for SMP, and to compare their potential influences on the physical, chemical and microbial properties of nonfat yogurts over a 12-day storage. All dry ingredients were added at 1% (w/v) concentration to yogurt milk. Yogurts differed from each other with different hardness values. Acetaldehyde contents of yogurts were in the range of 35 - 43 ppm. The acetaldehyde content of all yogurt types decreased during storage. The control yogurt had the most tyrosine content, and the WPI-fortified yogurt had the least. Using different dry dairy ingredients did not affect the numbers of starter cultures. In addition, no significant differences were observed among yogurt types regarding their mineral composition.
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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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    Formation kinetics of hydroxymethylfurfural and brown coloured compounds in goat milk during heating
    (Wiley, 2013) Guneser, Onur; Toklucu, Aysegul Kirca; Karagul-Yuceer, Yonca
    The formation of hydroxymethylfurfural, nonenzymatic brown coloured compounds and free sulphydryl groups in goat milk was studied during heating at 7595 degrees C. Analysis of kinetic data suggested that formation of hydroxymethylfurfural and nonenzymatic brown coloured compounds followed zero order reaction kinetics, while formation of free sulphydryl groups during heating varied depending on heating time. A good linear correlation (r = 0.839) was found between brown coloured compounds and hydroxymethylfurfural content in milk samples during heating. Activation energies (Ea) for the formation of hydroxymethylfurfural and nonenzymatic brown coloured compounds were 96.31 and 69.79 kJ/mol, respectively.
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    INFLUENCE OF SUPERCRITICAL CARBON DIOXIDE AND METHANOLIC EXTRACTS OF ROSEMARY ON OXIDATION AND SENSORY PROPERTIES OF WHEAT GERM OIL
    (Wiley-Hindawi, 2009) Yesil-Celiktas, Ozlem; Isleten, Muge; Karagul-Yuceer, Yonca; Bedir, Erdal; Vardar-Sukan, Fazilet
    Both supercritical CO2 and methanolic extracts from the leaves of rosemary (Rosmarinus officinalis) harvested from three different locations of Turkey at four different times of the year were added at a concentration of 100 mg/kg to wheat germ oil. Wheat germ oil samples were stored in an incubator for 10 days at 50C in order to promote oxidation and for the efficacy of the extracts for stabilization purposes to be examined. Degree of oxidation was determined by peroxide and p-anisidine values, which were performed every 2 days. Extracts from Mersin and Canakkale regions performed better results. Additionally, June and September harvests had lower peroxide values. According to the descriptive sensory analysis, both locations and extraction methods were found to effect flavor. Some flavor attributes, such as wheatlike/starchy, fishy and rubbery/metallic changed during storage regardless of locations and extraction methods. Supercritical CO2 extracts performed better results in terms of both oxidation and sensory properties. PRACTICAL APPLICATIONS From the perspective of the food industry, wheat germ oil stabilized with a natural antioxidant such as rosemary can be marketed as a functional product that can create a niche. Rosemary extracts containing higher amounts of rosmarinic acid and carnosic acid should be preferred in order to provide a better shelf life of an edible oil such as wheat germ oil.
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    Volatile compounds and proteolysis in traditional Beaten (Bieno sirenje) ewe's milk cheese
    (Wiley, 2014) Sulejmani, Erhan; Rafajlovska, Vesna; Guneser, Onur; Karagul-Yuceer, Yonca; Hayaloglu, Ali A.
    Beaten ewe's milk cheese is a traditional autochthonous type of cheese manufactured in Macedonia with a relatively high nutritional value and sensory characteristics. The objective of this study was to characterise the gross composition, proteolysis and volatile profiles of the cheese that is supplied from different retails. The ranges for gross composition were from 31.53% to 42.83% (w/w) for moisture, 41.99% to 50.98% (w/w) for fat-in-dry matter, 2.03% to 8.25% (w/w) for salt content and 20.74% to 33.35% (w/w) for protein. Proteolysis results showed various levels of soluble nitrogen ranged from 3.15 to 33.50 for water-soluble nitrogen (WSN) and from 1.11% to 6.79% for nitrogen soluble in 12% trichloroacetic acid (TCA-SN). The ranges for total free amino acids were from 1.65 to 8.06 mg Leu/g. Lower proteolysis was observed in the cheese samples due to high salt contents. In total, 65 volatile compounds were identified in Beaten cheese. As a conclusion, the variation of the peptide profile, electrophoresis and volatile contents of Beaten cheeses are due to the lack of standardised manufacture protocols.
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    Volatile metabolites produced from agro-industrial wastes by Na-alginate entrapped Kluyueromyces marxianus
    (Soc Brasileira Microbiologia, 2016) Guneser, Onur; Karagul-Yuceer, Yonca; Wilkowska, Agnieszka; Kregiel, Dorota
    The aim of this study was to evaluate the effects of alginate entrapment on fermentation metabolites of Kluyueromyces marxianus grown in agrowastes that served as the liquid culture media. K. marxianus cells entrapped in Na-alginate were prepared using the traditional liquid-droplet-forming method. Whey and pomaces from processed tomatoes, peppers, and grapes were used as the culture media. The changes in the concentrations of sugar, alcohol, organic acids, and flavor compounds were analyzed using gas chromatography-mass spectrometry (GC-MS) and high pressure liquid chromatography (HPLC). Both free and entrapped, K. marxianus were used individually to metabolize sugars, organic acids, alcohols, and flavor compounds in the tomato, pepper, grape, and acid whey based media. Marked changes in the fermentation behaviors of entrapped and free K. marxianus were observed in each culture. A 1.45-log increase was observed in the cell numbers of free K. marxianus during fermentation. On the contrary, the cell numbers of entrapped K. marxianus remained the same. Both free and entrapped K. marxianus brought about the fermentation of sugars such as glucose, fructose, and lactose in the agrowaste cultures. The highest volume of ethanol was produced by K. marxianus in the whey based media. The concentrations of flavor compounds such as ethyl acetate, isoamyl alcohol, isoamyl acetate, 2-phenylethyl isobutyrate, phenylethyl acetate, and phenylethyl alcohol were higher in fermented agrowaste based media compared to the control. (C) 2016 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda.