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    Characterization of binding interactions between green tea flavanoids and milk proteins
    (Elsevier Sci Ltd, 2010) Yuksel, Zerrin; Avci, Elif; Erdem, Yasar Kemal
    Flavanoids are known to interact with proteins to form complexes whose properties depend on the structure of both the flavanoids and the protein. In this study, the fluorescent probe binding method (fluorimetry analysis) and isothermal titration calorimetry (ITC) analysis were used to characterize binding interactions of green tea (GT) flavanoids and milk proteins. The hydrophobicity of the surface sites of milk proteins was estimated using the reconstituted milk-green tea and casein-green tea systems. Reconstituted milk-green tea and casein-green tea samples were prepared with different solid-non-fat (SNF) and casein (Cn) concentrations, respectively. It was observed that the number of surface hydrophobic sites decreased in the presence of GT flavanoids for all SNF and Cn concentrations. The decrease in protein surface hydrophobicity was explained by the hydrophobic binding between milk proteins and GT flavanoids. The binding enthalpies obtained from ITC analysis implied that interaction was non-covalent between catechin and beta-casein. (C) 2009 Elsevier Ltd. All rights reserved.
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    Modification of the renneting process in Berridge substrate by transglutaminase
    (Wiley, 2011) Yuksel, Zerrin; Avci, Elif; Erdem, Yasar Kemal
    The influence of enzymatic cross-linking on the rennet coagulation of Berridge substrate was investigated in the rennet gel samples prepared by three different methods using a microbial Tgase. Protein cross-linking was carried out at each of three stages: before the addition of rennet, simultaneously with rennet and after the addition of rennet. The results showed that the cross-linking of milk proteins before the addition of rennet inhibited the primary enzymatic phase of rennet coagulation. It was observed that enzymatic cross-linking affected both the primary and the secondary phases of rennet coagulation. The most suitable application method was the addition of transglutaminase at the 5th minute after the addition of rennet.
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    Physicochemical and Microbiological Characterization of Protected Designation of Origin Ezine Cheese: Assessment of Non-starter Lactic Acid Bacterial Diversity with Antimicrobial Activity
    (Korean Soc Food Science Animal Resources, 2019) Uymaz, Basar; Akcelik, Nefise; Yuksel, Zerrin
    Ezine cheese is a non-starter and long-ripened cheese produced in the Mount of Ida region of Canakkale, Turkey, with a protected designation of origin status. Nonstarter lactic acid bacteria (NSLAB) have a substantial effect on the quality and final sensorial characteristics of long-ripened cheeses. The dominance of NSLAB can be attributed to their high tolerance to the hostile environment in cheese during ripening relative to many other microbial groups and to its ability to inhibit undesired microorganisms. These qualities promote the microbiological stability of long-ripened cheeses. In this study, 144 samples were collected from three dairies during the ripening period of Ezine cheese. Physicochemical composition and NSLAB identification analyses were performed using both conventional and molecular methods. According to the results of a 16S rRNA gene sequence analysis, 13 different species belonging to seven genera were identified. Enterococcus faecium (38.42%) and E. faecalis (18.94%) were dominant species during the cheese manufacturing process, surviving 12 months of ripening together with Lactobacillus paracasei (13.68%) and Lb. plantarum (11.05%). The results indicate that NSLAB contributes to the microbiological stability of Ezine cheese over 12 months of ripening. The isolation of NSLAB with antimicrobial activity, potential bacteriocin producers, yielded defined collections of natural NSLAB isolates from Ezine cheese that can be used to generate specific starter cultures for the production of Ezine cheese (PDO).
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    The influence of enzymatic cross-linking of proteins on the Maillard reaction in milk
    (Wiley, 2014) Yuksel, Zerrin
    The influence of transglutaminase (TGase) on the Maillard reaction was investigated in skimmed milk samples during heat treatment. TGase-treated and control samples were heated at 80, 120 and 140 degrees C for 1, 5, 15, 30, 40 and 60min. Compared with the TGase-treated samples heated at 80 and 120 degrees C, the sample heated at 140 degrees C showed a larger decrease in furosine concentration. It was also found that TGase did not affect the formation of hydroxymethylfurfural and lactulose at 120 degrees C, whereas their concentrations increased in the presence of TGase at 140 degrees C. It was concluded that blockage of lysine residues via enzymatic cross-linking of milk proteins had a limited effect on the Maillard reaction.
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    The influence of transglutaminase treatment on functional properties of set yoghurt
    (Wiley, 2010) Yuksel, Zerrin; Erdem, Yasar K.
    The objective of this study was to investigate the effect of transglutaminase (Tgase) on the functional properties of set yoghurt, due to enzymatic cross-linking of the milk proteins. Yoghurt samples were prepared from three formulations: reconstituted skim milk, and whole milk containing two different solid-non-fat (SNF) content, with four enzyme treatments: Control (no enzyme) and three microbial Tgase treatments: Pre-incubated 90 min, Pre-incubated and inactivated after 90 min, Not pre-incubated. The modifications which were caused by Tgase were found to be more clear when Tgase was active in set type yoghurts. It was found that nonfat yoghurt sample with lower SNF content can be produced with improved textural properties using Tgase.