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Application of Ultrafiltration to Produce High Solid Content Yogurt

Tadayon Saeedi, Behnaz | 2008

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53876 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Roosta Azad, Reza; Razavi, Jalil
  7. Abstract:
  8. Labneh is a semisolid product that is produced by concentrating milk to approximately 23% total solids (wt/vol) by the traditional cloth bag method, ultrafiltration and direct reconstitution. For ultrafiltration membrane processing is carried out either before or immediately after fermentation. The effect of storage time on the flow properties of concentrated yogurt (labneh) was investigated using a rotational viscometer. Experiments were performed at after 0, 2, 5 and 14 days after production. The apparent viscosity of fresh sample was then measured as a function of shear rate. For a given shear rate, the apparent viscosity was measured as a function of shearing time. The increase in the apparent viscosity of fresh labneh with storage time is attributed to the further development of the gel structure occurred. It was also found that, labneh samples exhibited shear-thinning and thixotropic behaviours with different storage times. The shear-thinning behaviour is fitted well by the power-law model, and the effect of temperature on the power-law parameters was determined. The thixotropic behaviour of labneh was modelled using the second order structural kinetic approach. Development of the gel structures during incubation was monitored discontinuously using a stress-controlled oscillatory dynamic rheometer. The complex modulus (G*) and loss tangent (tan) were measured as functions of amplitude at 10 (Hz) frequency. The complex modulus (G*) of the higher protein system (UF-milk) continued to increase with time
  9. Keywords:
  10. Ultrafiltration ; Shear Thining Fluid ; Labneh ; Dynamic Rheology ; Thixotropic ; Rotational Viscometer ; Rheological Properties

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