Yonca Karagül-Yüceer

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.

Volatile metabolites produced from agro-industrial wastes by Na-alginate entrapped Kluyveromyces marxianus

The aim of this study was to evaluate the effects of alginate entrapment on fermentation metabolites of Kluyveromyces 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.