The effects of empirical viscosity measuring techniques that are commonly used in the determination of the viscosity of weak viscoelastic gels such as yoghurt on the microstructure of yoghurt were investigated by scanning electron microscopy (SEM). | Turk J Agric For 28 (2004) 19-23 © TÜB‹TAK Destructive Effects of Classical Viscosimeters on the Microstructure of Yoghurt Gel Barbaros ÖZER* Harran University, Faculty of Agriculture, Department of Food Engineering, 63040 Eyyubiye, fianl›urfa - TURKEY Received: Abstract: The effects of empirical viscosity measuring techniques that are commonly used in the determination of the viscosity of weak viscoelastic gels such as yoghurt on the microstructure of yoghurt were investigated by scanning electron microscopy (SEM). In the measurement of viscosity, Brookfield and Haake viscosimeters were employed at 2 different measuring periods (15 and 30 s). The results obtained indicated that the increase in the measuring period (15 s versus 30 s) stimulated the further destruction of the casein gel network. Additionally, the Brookfield viscosimeter was more destructive than the Haake viscosimeter. In general, lower viscosity values were in good harmony with higher destruction in the gels, as shown by SEM micrographs. Key Words: Viscosity, Yoghurt, Destruction Klasik Viskozimetrelerin Yo¤urt Mikroyap›s› Üzerindeki Tahrip Etkisi Özet: Bu çal›flmada, yo¤urt benzeri zay›f viskoelastik jellerin p›ht› stabilitelerinin ölçümünde s›k kullan›lan emprik viskozite ölçüm tekni¤inin yo¤urdun mikroyap›s› üzerine etkileri taray›c› elektron mikroskobu (scanning electron microscopy, SEM) yard›m› ile incelenmifltir. Viskozite ölçümlerinde Brookfield ve Haake viskozimetrelerinden yararlan›lm›fl ve iki farkl› ölçüm süresi (15 ve 30 saniye) deneme kapsam›na al›nm›flt›r. Elde edilen sonuçlar ›fl›¤›nda, ölçüm süresinin artmas› ile birlikte kazein jellerinin p›ht› tahribat› da art›fl göstermifltir. Ayr›ca, Brookfield viskozimetresinin Haake viskozimetresine oranla daha fazla deformasyon etkisi yaratt›¤› da belirlenmifltir. Genel olarak, SEM foto¤raflar›ndan da görüldü¤ü üzere, düflük viskozite de¤erleri ile jel yap›s›ndaki parçalanma düzeyi aras›ndan önemli bir iliflkinin varl›¤› .
