Süt ve rekonstitüe sütün ohmik ısıtılmasının incelenmesi: reolojik özellikleri üzerine etkisinin belirlenmesi

Bu çalışmada, eşdeğer yağ ve kuru madde içeriğine sahip tam yağlı süt ve rekonstititüe süt örneklerinin ohmik ısıtılmasının reolojik özellikleri üzerine etkisi incelenmiştir. Örnekler 30 V/cm voltaj gradyanında 20 °C’den 80 °C’e kadar ohmik olarak ısıtılmışlardır. Kontrol amaçlı olarak eşdeğer ısıl geçmişe sahip su banyosunda ısıtma işlemi de gerçekleştirilmiştir. Her iki ısıtma yöntemi sırasında, kıvam özelliklerinin değişimi eş merkezli silindirik tip viskometre kullanılarak belirlenmiştir. Uygulanan ısıtma yönteminin ve örnek çeşidinin viskozite değerlerindeki değişim üzerine etkisinin istatistiksel olarak önemli düzeyde olduğu saptanmıştır. Viskozitenin, rekonstitüe süt örnekleri için ohmik ısıtma, süt örnekleri için ise geleneksel ısıtma sırasındaki sıcaklık artışına daha hassas olduğu belirlenmiştir. Bu çalışmada elde edilen veriler kurulacak pilot ve endüstriyel çaptaki sürekli ohmik ısıtma sistemlerinin tasarımında, özellikle pompalama gereksinimi ve ohmik ısıtma ünitesi içinde akış profillerinin değişimi açısından dikkate alınmalıdır. Ohmik ısıtıcı içinde oluşacak hız profillerindeki kararlılığın sağlanabilmesi homojen ısıtma için kaçınılmazdır.

The investigation on ohmic heating of milk and reconstituted milk: effects on rheological behaviour

In this study, the effect of ohmic heating on rheological behaviour of milk and milk powder reconstitutes was investigated. Samples were heated from 20°C to 80 °C at 30 V/cm voltage gradient by ohmic heating. Samples were also heated at water bath for the purpose of control heating. The change of rhelogical properties during both heating methods were determined by using concentric-cylinder type viscometer. The heating method and the type of the sample were statistically significant on the change of viscosity. It was found that the viscosity was more sensible to temperature change for milk powder solution samples during ohmic heating or for milk during control heating. The data obtained must be taken into account in the design of pilot and industrial scale continuous ohmic heating systems, especially in the estimation of pumping requirement and the change of velocity profiles within ohmic heating unit. The steady velocity profiles within the system are essential for homogeneous heating.

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