Auty.pdfJournal of Dairy Research (2001) 68 417±427. Printed in the United Kingdom 417Development and application of confocal scanning lasermicroscopy methods for studying the distribution of fat and proteinin selected dairy productsBy MARK A. E. AUTY"*, MYRA TWOMEY", TIMOTHY P. GUINEE"and DANIEL M. MULVIHILL#Rheology of milk chocolateSamples of each chocolate were taken at the end of the conching stage andrheological properties were measured at 40 °C using a stress-controlled rheometer asdescribed by Twomey et al. 2000. Casson yield value and Casson viscosity werecalculated using the Casson equation (OICC, 1973).

Engman_01.pdf – equation approach

Engman_02.pdf

SEMI-SOLID PROCESSING OF CHOCOLATEAND COCOA BUTTERThe Experimental Correlation of ProcessRheology with MicrostructureJ. ENGMANN and M. R. MACKLEY_Department of Chemical Engineering, University of Cambridge, Cambridge, UKIn this paper we use a double-piston multi-pass rheometer(Mackley et al., 1995) to subject chocolate or cocoa butter to successive multiple extrusions and therebye establish how the material responds to different process histories.

The Multi-Pass RheometerThe ‘Cambridge MultiPass Rheometer’ (MPR), shown schematically in Figure 4, is a double-piston capillary rheometer that allows repeated processing of samples at a controlled temperature and mean hydrostatic pressure. As the sample is completely enclosed within the rheometer, evaporation, drying or other artefacts caused by free surfaces are avoided (Wee and Mackley, 1998). The device enables a single sample to be processed many times in a systematic and controlled way. After the material under test has been loaded into the MPR, the mean hydrostatic pressure within the test section can be fixed by moving the pistons towards each other. Subsequently the two pistons are moved together in the same direction in a synchronized fashion to conduct the tests. In the tests reported in this paper the pistons move together at a constant speed and for a set time. There is then a rest time before the piston motion is reversed and the process repeated, which could vary between a fraction of a second or hours. In this way, the test material can be subjected to successive processing through a capillary section under very controlled conditions. Two pressure transducers are positioned above and below the test section capillary and this enables time-dependent measurements of differential pressure between these two locations to be made (Mackley and Spitteler, 1996; Ranganathan et al., 1999). The ‘MPR

Mark3’, or MPR3, was used for the experiments described in this paper. This instrument has barrel diameters of 15 mm and the capillaries used had an internal diameter of 4 mm, 10 mm length and an entry angle of 458. In addition to these process rheology measurements, it is possible to use the MPR3 together with an X-ray scattering facility (Mackley et al., 2000) and Figure 5 is a schematic representation of the MPR and X-ray configuration. In this case a beryllium capillary (to allow sufficient transmission of X-rays) is used in the test section and in situ X-ray data can be obtained during MPR processing, which enables simultaneous measurements of microstructure and process rheology. The X-ray system used for the in situ diffraction measurements consisted of a Siemens Kristalloflex 760 generator (sealed tube type; maximum power 2.2 kW), graphite monochromator (Huber), beam collimator and a twodimensional detector (Siemens HI-STAR). The whole system was mounted inside a metallic cabinet built on a moveable trolley and could be set up around the MPR. The X-ray detector could be positioned at different angles in order to study different parts of the diffraction spectrum.

Mulji_01.pdf

0960–3085/03/$23.50+0.00# Institution of Chemical Engineerswww.ingentaselect.com=titles=09603085.htm Trans IChemE, Vol 81, Part C, June 2003

MICROSTRUCTURE AND MECHANICAL PROPERTYCHANGES IN COLD-EXTRUDED CHOCOLATEN. C. MULJI1, M. E. MIQUEL2, L. D. HALL2 and M. R. MACKLEY1

1Department of Chemical Engineering, University of Cambridge, Cambridge, UK2Herchel Smith Laboratory for Medicinal Chemistry, University of Cambridge, Cambridge, UK

A Davenport capillary rheometer was used to make extrudates for the cube compression tests, at 20°C. It is a constant-velocity, vertical, batch extruder. Extrudates were produced using an aluminium square exit die (7x7 mm) with a land length of 10mm and a processing rate of 0.785cm3 s-1. The extrudates were then immediately cut to a length of 7mm using a blade.

Kilcast_01.pdf

Sensory perception of creaminess and its relationship withfood structure§David Kilcast*, Stuart CleggLeatherhead Food RA, Randalls Rd, Leatherhead, Surrey KT22 7RY, UKReceived 1 April 2002;received in revised form 13 May 2002;accepted 20 June 2002

Rheological measurements were made using a CarriMed controlled stress rheometer (model CSL2100, TA Instruments, Leatherhead, UK). A sample was loaded onto the plate of the rheometer and oil was applied around the boundary of the cone to prevent sample evaporation. Measurements on the model systems and artificial creams were carried out at both 5 and 37 °C to assess any differences between serving and body temperature. Measurements on the

chocolate mousses were carried out at 20 °C. Firmness of the chocolate mousses was measured at 5 °C using a Stable Micro Systems TAXT2 Texture Analyser (Stable Micro Systems, Godalming, UK), using a 35-mm diameter cylindrical probe set to penetrate to a depth of 8 mm at a rate of 1 mm/s and then return to the start point, again at a rate of 1 mm/s. Results were averaged over three replicate measurements.

Particle size analysis of the model particle systems and determination of the oil droplet size distribution in the artificial creams were performed using a Malvern Mastersizer(Malvern Instruments Ltd, Malvern, UK). The air bubble size of the chocolate mousses was measured using an Optimas Image Analysis System (Optimas Corporation, Washington, USA). Images obtainedfrom light and confocal microscopy were analysed to obtain the required bubble size information.

Liang_01.pdf

J. Dairy Sci. 87:20–31American Dairy Science Association, 2004.

Effects of Milk Powders in Milk ChocolateB. Liang and R. W. HartelDepartment of Food Science,University of Wisconsin,1605 Linden Drive, Madison 53706

Melt rheologyRheological properties of the chocolate mass at 40°C were characterized by use of a Brookfield DV-1 HATD viscometer (Stoughton, MA) with a small sample adapter (SC4-13R) and spindle (SC4-21), according to the international guidelines (Office International du Cocao et du Chocolat, 1973). The chocolate mass was stabilized for 10 min in the temperaturecontrolled cup and presheared at 20 RPM for 5 min prior to measurement. Ascending (0.5 to 100 rpm) and descending (100 to 0.5 rpm) tests were performed for each sample. Torque readings at each shear rate were recorded after 30 s of shearing for duplicate samples.

The data were analyzed according to the modified Casson model of fluid rheology (Steiner, 1958)

(1 + a)τ0.5 = 2τ c 0.5 + (1 + a)η c

0.5γ0.5, [2]

where τ is shear stress (obtained from torque data) and γ is shear rate (obtained from rpm data). The two parameters used to fit the Casson model are τc, the Casson yield value, and ηc, the Casson plastic viscosity.

Sokmen_01.pdf

LWT 39 (2006) 1053–1058

Influence of some bulk sweeteners on rheological properties of chocolateAhmet Sokmen, Gurbuz Gunes_

Food Engineering Department, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, 34469 Istanbul, TurkeyReceived 21 September 2005; received in revised form 17 February 2006; accepted 9 March 2006

2.4. Rheological measurementsRheological properties of the chocolate samples were measured using a shear rate-controlled rheometer (Haake Rotovisco RT 20, Thermo Electron Corp., Karlsruhe, Germany) with a concentric cylinder system (sensor Z40 DIN) according to IOCCC method (Aeschlimann & Beckett, 2000). The ratio of inner radius to outer radius was 0.92 in the concentric cylinder system. Each chocolate sample was incubated at 50 C for 75 min for melting and transferred to the rheometer cub, sheared at 5 s-1 rate for 10 min at 40 C in rheometer before the measurement cycles started. Shear stress was measured at 40 C as function of increasing shear rate from 5 to 60 s-1 (ramp up) within 120 s, then decreasing the shear rate from 60 to 5 s-1 (ramp down), and in each ramp 50 measurements were taken. This measurement cycle was repeated 30 times consecutively until thixotropy in the samples were eliminated. The data from the 30th measurement were applied to Casson, Bingham and Herschel–Bulkley models. Each of the duplicate samples of chocolate was measured once in the rheometer. The best model was selected by statistical analysis and all rheological parameters (viscosity, yield stress, flow behavior index) were calculated using the best model.Afoakwa_06.pdf

Rheological measurements of molten dark chocolateRheological behaviour was characterised using steady shear measurements carried out in a shear rate- controlled rheometer [Thermo Haake ViscoTester 550 (VT 550); Thermo Electron Corp., Karlsruhe, Germany]. This used bob and cup (recessed end) geometry (Sensor SAVI and SVII), as for IOCCC method (Aeschlimann & Beckett, 2000) with a ratio of inner to outer radius of 0.92 in the concentric cylinder system. The samples were incubated at 50 °C for 75 min for melting and transferred, pre-sheared at 5 s -1 for 15 min at 40 °C, before measurement cycles. Shear stress was measured at 40 °C as a function of increasing shear rate from 5 to 50 s-1 (ramp up) over 120 s, then decreasing from 50 to 5 s-1 (ramp down); within each ramp, 50 measurements were taken. Temperature was controlled using Haake K20 Ther- mo-regulator (Thermo Electron Corp.). The mean value and standard deviation of triplicate readings were recorded.

Casson plastic viscosity and Casson yield values were calculated from interpolation data using Thermo Haake RheoWin Pro 297 Software by the least squares method. Other rheological parameters (yield stress, apparent viscosity and thixotropy) were deduced from data as recommended by ICA (2000) and Servais et al. (2004) with some modifications. Value of stress at a shear rate of 5 s-1 represented yield stress, viscosity ata shear of 30 s-1, apparent viscosity, and difference between yield stresses at 5 s-1 during ramp up and down, thixotropy.

Afoakwa_05.pdf

Effects of particle size distribution and compositionon rheological properties of dark chocolateEmmanuel Ohene Afoakwa Æ Alistair Paterson ÆMark FowlerRheological measurementsThe rheological behavior of molten dark chocolate was characterized using steady shear measurements. All measurements were carried out in shear rate-

controlled rheometer (Thermo Haake ViscoTester 550 (VT 550), Thermo Electron Corp., Karlsruhe, Germany) using bob and cup (Recessed end) geometry (Sensor SVI and SVII), as for IOCCC method [22] with a ratio of inner to outer radius of 0.92 in the concentric cylinder system. Samples were incubated at 50 °C for 75 min for melting and transferred, pre-sheared at 5 s–1 rate for 15 min at 40 °C, before measurement cycles. Shear stress was measured at 40 °C as function of increasing shear rate from 5 to 50 s–1 (ramp up) within 120 s, then decreasing from 50 to 5 s–1 (ramp down), within each ramp 50 measurements were taken. Temperature of the chocolates samples was controlled during the experiment using Haake K20 Thermo-regulator (Thermo Electron Corp., Karlsruhe, Germany), and solvent trap was used to prevent water evaporation. Mean value and standard deviation of triplicate readings were recorded.The Casson model was used to calculate Casson plastic viscosity and Casson yield values from interpolation data using ThermoHaake RheoWin Pro 297 Software by the least square method.The Casson model equation is denoted by: Other rheological parameters (yield stress, apparent viscosity and thixotropy) were deduced from data as recommended by ICA [8] and Servais et al. [3] with some modifications. Value of stress at a shear rate of 5 s–1 represented yield stress, viscosity at a shear of 30 s–1, apparent viscosity; and difference between yield stress at 5 s–1 during ramp up and down, thixotropy.