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Benyamin Asadipour-Farsani [EngD Conference abstract]

Benyamin Asadipour-Farsani [EngD Conference abstract]

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Effect of processing conditions on the physical properties of fat systems<strong>Benyamin</strong> <strong>Asadipour</strong>-<strong>Farsani</strong> a,b , Peter Sadd a , Thomas Mills b , Fotios Spyropoulos b , Ian Norton b ,aPremier Foods Central Technical, The Lord Rank Centre, High Wycombe HP12 3QSbSchool of Chemical Engineering, University of Birmingham, Edgbaston B15 2TTFats are employed in many industries such as food, cosmetic and pharmaceuticals. Manyimportant functional properties of fat-containing products are dictated by the characteristicsof the crystal network formed by the constituent lipid species (1) . Fat is a crucial contributor toseveral texture attributes such as creaminess, softness, melting in the mouth, juiciness andthickness, most of which are desired and are therefore positively regarded qualities in foodproducts (2) , however there is increasing demand for healthier, lower fat products byconsumers. Lipids also contribute to the texture of baked products by interacting withproteins and polysaccharides and a further role of fats in foods is to carry aroma compoundswhich are generally hydrophobic or at least have hydrophobic fragments (3) . This work willinvestigate the effect of processing conditions on the physical properties of fat crystalnetworks.Experiments were carried out to study the effects of processing conditions on fat systemscontaining 5% tripalmitin and 95% rapeseed oil using a scraped surface heat exchanger. Theprocessing conditions studied were the heat exchanger’s mixing speed, cooling temperatureand throughput. Rheological studies were conducted to characterise the material properties ofthe fat systems. Viscosity measurements were carried out to study the effects of processingconditions on the material behaviour. Oscillatory rheology was used to study the viscoelasticbehaviour of the fat systems. Amplitude sweeps and oscillation tests (small scale rheologicalanalysis) were conducted to study the viscous modulus (G’’) and the elastic modulus (G’) ofthe system which is an indicator of the macroscopic consistency of the network. The meltingbehaviour of the fat system was studied using differential scanning calorimetry (DSC).Viscosity, Pa.s1.E+41.E+31.E+21.E+11.E+01.E-11.E-3 1.E-2 1.E-1 1.E+0 1.E+1 1.E+2 1.E+3 1.E+4Shear rate, s -1 15°C15°C reverse10°C10°C reverse5°C5°C reverse2°C2°C reverseFigure 1: Fat rheology modification by the use of different coolant temperatures.


Figure 1 illustrates how the coolant temperature of the scraped surface heat exchanger affectsthe viscosities of fat systems. Three different behaviours are observed. The first is that ofsamples produced at low temperatures (i.e. 2°C and 5°C), which show shear thinningbehaviour and signs of structural deformation. The second is that of samples made at a hightemperature (i.e. 15°C). Such samples initially exhibit slightly shear-thickening behaviourfollowed by a significant decrease in the viscosity, indicating the shear-thinning nature ofsolid fat networks; and have a higher viscosity at the end of the viscometry experiment,compared to that at the start of the experiment. So the application of shear has altered themicrostructure of the systems in such a way that results in an increase in viscosity. The thirdviscosity profile observed is that of samples produced at 10°C, which show an intermediatebehaviour to that of the two viscosity profiles previously mentioned. A slight increase inviscosity is observed when comparing the values at the start and the end of the experiment,on the other hand the viscosity profile at higher shear rates is similar to that of samplesproduced at lower temperatures.Results obtained from these experiments provide an insight into the effect of processingconditions on the physical properties of fat crystal networks. This allows the design ofsystems with specific behaviour by manipulating the processing conditions.References(1) Effect of cooling rate on the structure and mechanical properties of milk fat and lard.Campos, R., Narine, S. S. and Marangoni, A. G. s.l. : Elsevier Science Ltd., 2002, FoodResearch International, Vol. 35, pp. 971-981.(2) SIKORSKI, Z. E. and SIKORSKA-WISNIEWSKA, G. The Role of Lipids in Food Quality. [bookauth.] C. WILLIAMS and J. BUTTRISS. Improving the Fat Content of Foods. s.l. : WoodheadPublishing, 2006.(3) Crystallization behaviour of fats and lipids - a review. Sato, Kiyotaka. s.l. : Elsevier ScienceLtd., 2001, Chemical Engineering Science, Vol. 56, pp. 2255-2265.

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