Onur Güneşer

Characterization of aroma-active compounds, sensory properties, and proteolysis in Ezine cheese.

Ezine cheese is a white pickled cheese ripened in tinplate containers for at least 8 mo. A mixture of milk from goat, sheep, and cow is used to make Ezine cheese. Ezine cheese has geographical indication status. The purposes of this study were to determine and compare the changes in basic composition, aroma, and sensory characteristics, and proteolytic activity of Ezine cheese stored in tinplate containers and plastic vacuum packages during storage. Aroma-active compounds were determined by thermal desorption gas chromatography olfactometry. To evaluate the proteolytic activity, casein and nitrogen fractions were determined. The results indicated that compounds identified at high intensities were dimethyl sulfide, ethyl butyrate, hexanal, ethyl pentanoate, (Z)-4-heptenal, 1-octen-3-one, acetic acid, butyric acid, and p-cresol. Characteristic descriptive terms were cooked, whey, creamy, animal-like, sour, and salty. The level of proteolysis increased in Ezine cheese during storage. Ezine cheese can be ripened in small-size packaging after 3 mo of storage. Approximately 6 mo is sufficient to produce the characteristic properties of Ezine cheese.

Effect of ultraviolet light on water- and fat-soluble vitamins in cow and goat milk

The objective of this study was to investigate and compare the effects of UV light and heat treatment on vitamins A, B(2), C, and E in cow and goat milk. Vitamins were analyzed by reverse-phase high-pressure liquid chromatography. Ultraviolet and pasteurization treatments caused loss in vitamin C in milk. Pasteurization did not have any significant effect on vitamin B(2). However, UV light treatment decreased the amount of vitamin B(2) after several passes of milk through the UV system. In addition, UV light treatment decreased the amount of vitamins A and E. Vitamins C and E are more sensitive to UV light. UV light sensitivities of vitamins were C>E>A>B(2). These results show that UV light treatment decreases the vitamin content in milk. Also, the number of passes through the UV system and the initial amount of vitamins in milk are important factors affecting vitamin levels.

Influence of carbon and nitrogen source on production of volatile fragrance and flavour metabolites by the yeast Kluyveromyces marxianus

The yeast Kluyveromyces marxianus produces a range of volatile molecules with applications as fragrances or flavours. The purpose of this study was to establish how nutritional conditions influence the production of these metabolites. Four strains were grown on synthetic media, using a variety of carbon and nitrogen sources and volatile metabolites analysed using gas chromatography–mass spectrometry (GC–MS). The nitrogen source had pronounced effects on metabolite production: levels of the fusel alcohols 2‐phenylethanol and isoamyl alcohol were highest when yeast extract was the nitrogen source, and ammonium had a strong repressing effect on production of 2‐phenylethyl acetate. In contrast, the nitrogen source did not affect production of isoamyl acetate or ethyl acetate, indicating that more than one alcohol acetyl transferase activity is present in K. marxianus. Production of all acetate esters was low when cells were growing on lactose (as opposed to glucose or fructose), with a lower intracellular pool of acetyl CoA being one explanation for this observation. Bioinformatic and phylogenetic analysis of the known yeast alcohol acetyl transferases ATF1 and ATF2 suggests that the ancestral protein Atf2p may not be involved in synthesis of volatile acetate esters in K. marxianus, and raises interesting questions as to what other genes encode this activity in non‐Saccharomyces yeasts. Identification of all the genes involved in ester synthesis will be important for development of the K. marxianus platform for flavour and fragrance production. Copyright

Pigment and color stability of beetroot betalains in cow milk during thermal treatment

Thermal stability of beetroot betalains in cow milk was determined during heating at 70-90 °C. Changes in color values of colored milk were also investigated. Degradation of betalains followed first order kinetics while changes of L(∗), Hue angle and Chroma values fitted zero order and first order kinetic, respectively. Reaction rate for degradation of betalains, L(∗), Hue angle and Chroma values ranged between 1.588-30.975 × 10(-3) min(-1), 90.50-379.75 L(∗)min(-1), 0.581-5.008 Hue anglemin(-1) and 3.250-19.750 × 10(-3) min(-1), respectively. Between 70 and 90 °C, activation energy for the degradation of betalains was 42.449 kJ mol(-1). L(∗) values was more stable than Hue angle and Chroma color values in colored milk during heating. 74.150 kJ mol(-1), 111.174 kJ mol(-1) and 93.311 kJ mol(-1) of activation energy values were found for L(∗), Hue angle and Chroma values of milk, respectively. Significant positive and negative linear correlations were determined between betalains and color values. Multiple regression models were also established to predict the content of betalains in milk during thermal process by using color values.

Growth and by-product profiles of Kluyveromyces marxianus cells immobilized in foamed alginate.

The aim of this research was to study how the yeast cell immobilization technique influences the growth and fermentation profiles of Kluyveromyces marxianus cultivated on apple/chokeberry and apple/cranberry pomaces. Encapsulation of the cells was performed by droplet formation from a foamed alginate solution. The growth and metabolic profiles were evaluated for both free and immobilized cells. Culture media with fruit waste produced good growth of free as well as immobilized yeast cells. The fermentation profiles of K. marxianus were different with each waste material. The most varied aroma profiles were noted for immobilized yeast cultivated on apple/chokeberry pomace. Copyright

Production of flavor compounds from olive mill waste by Rhizopus oryzae and Candida tropicalis

The purpose of this study was to investigate the production of flavor compounds from olive mill waste by microbial fermentation of Rhizopus oryzae and Candida tropicalis. Olive mill waste fermentations were performed in shake and bioreactor cultures. Production of flavor compounds from olive mill waste was followed by Gas Chromatography–Mass spectrometry, Gas chromatography- olfactometry and Spectrum Sensory Analysis®. As a result, 1.73-log and 3.23-log cfu/mL increases were observed in the microbial populations of R. oryzae and C. tropicalis during shake cultures, respectively. C. tropicalis can produce a higher concentration of d-limonene from olive mill waste than R. oryzae in shake cultures. The concentration of d-limonene was determined as 185.56 and 249.54 μg/kg in the fermented olive mill waste by R. oryzae and C. tropicalis in shake cultures respectively. In contrast, R. oryzae can produce a higher concentration of d-limonene (87.73 μg/kg) d-limonene than C. tropicalis (11.95 μg/kg) in bioreactor cultures. Based on sensory analysis, unripe olive, wet towel, sweet aromatic, fermented aromas were determined at high intensity in olive mill waste fermented with R. oryzae meanwhile olive mill waste fermented with C. tropicalis had only a high intensity of unripe olive and oily aroma.

Bioflavour production from tomato and pepper pomaces by Kluyveromyces marxianus and Debaryomyces hansenii

Bioflavours are called natural flavour and/or fragrance compounds which are produced using metabolic pathway of the microorganism and/or plant cells or their enzyme systems with bioengineering approaches. The aim of this study was to investigate bioflavour production from tomato and red pepper pomaces by Kluyveromyces marxianus and Debaryomyces hansenii. Obtained specific growth rates of K. marxianus and D. hansenii in tomato pomace were 0.081/h and 0.177/h, respectively. The bioflavour profile differed between the yeasts. Both yeasts can produce esters and alcohols such as phenyl ethyl alcohol, isoamyl alcohol, isoamyl acetate, phenyl ethyl acetate and isovaleric acid. “Tarhana” and “rose” were descriptive flavour terms for tomato and pepper pomaces fermented by K. marxianus, respectively. Tomato pomace fermented by D. hansenii had the most intense “green bean” flavour while “fermented vegetable” and “storage/yeast” were defined as characteristic flavour terms for pepper pomaces fermented by D. hansenii.

Volatile compounds and proteolysis in traditional Beaten (Bieno sirenje) ewe's milk cheese

Beaten ewes 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.

Different Bioengineering Approaches on Production of Bioflavor Compounds

Abstract Flavor compounds are generally used as food additives and mostly produced through artificial means—that is, chemical synthesis or by extraction from plant and animal sources. The increasing consumer preference for natural products has promoted significant efforts toward the biotechnological production of these compounds (bioflavor). There are two kinds of aroma and flavor production via biotechnological process, de novo microbial processes and bioconversions of natural precursors using microbial cells or enzymes. The production of bioflavors with microorganisms and enzymes is illustrated by the discussion of the current state of the art developments in this field. Efforts at production of flavor compounds often lack economic profitability, mainly due to low productivities or low concentrations of target compounds in fermentation broth. This chapter reviews also the current state of the art of bioprocess used for the production of flavor and fragrance compounds, with emphasis on different ways used to improve process productivity. Bioengineering provides promising technical options for increasing the productivity with bioflavor production, such as different fermentation strategies (batch, fed-batch, and continuous fermentation), gas-phase or two-phase reactions, specific reactor constructions such as membrane, solid-state or closed loop reactors, optimization and modeling approaches of bioprocess and in situ recovery of product.

EFFECTS OF THE DURATION OF HEAT TREATMENT AND RIPENING ON THE FORMATION OF BIOGENIC AMINES IN EZINE CHEESE

The purpose of this study is to investigate the effects of the different durations of thermal processing on the formation of biogenic amine and changes in microbial profile in Ezine cheese during ripening. Ezine cheese samples were produced by thermal processing at 65oC for 10 min and 30 min. The biogenic amines histamine, putrescine, cadaverine, tyramine, tryptamine, and phenylethylamine were identified by high performance liquid chromatography. Moreover, the enumeration of the psychrophilic aerobic and mesophilic aerobic bacteria, lactic acid bacteria, fecal coliform, total yeast and mold Enterobacteriaceae, Escherichia coli and Clostridium perfiringens was conducted for the purpose of the study. No biogenic amine was observed in the fresh cheese samples, while the amounts of biogenic amines in cheese samples were observed to have increase during the ripening. The amounts of the biogenic amines in the Ezine cheese samples were determined to pose no health-related risks. The effect of heat treatment duration on counts of mesophilic aerobic bacteria and lactic acid bacteria in the Ezine cheese samples were observed to have varied depending on storage duration.