Processing Parameters in Ice Cream Model Mix Manufacturing: effects of pasteurization and ageing time 1BAZMI A., *DUQUENOY A., SOMMIER A., CUVELIER G., LAUNAY B., *RELKIN P. Ecole Nationale Supérieure des Industries Alimentaires, UMR (SCALE et GENIAL), 1, Avenue des Olympiades-F-91 744 Massy. 1PhD Student with scholar-ship grant from TABRIZ University - Iran. * Corresponding authors: relkin@ensia.fr, duquenoy@ensia.fr Introduction In the fabrication procedure of dairy emulsions, pasteurization operation is applied for destruction of pathogenic bacteria. Meanwhile, food components could be affected, e.g. from the extensive literature of the past years, we know that whey proteins of milk denature in the pasteurization temperature range (75-80°C) (Relkin, 1996; Kulozik et al., 2003; Livney et al., 2003), and have consequence on physico-chemical interactions and structural properties of dairy whipped creams (Sourdet et al., 2003). Likely for other dairy whipped dairy emulsions, and following pasteurization, homogenization and prior to whipping, Ice cream mix is stored overnight at 4°C for ageing. This period is accompanied by milk fat crystallization, re-organization of milk fat globules and also hydration of proteins and hydrocolloids Berger, 1990; Olsen, 1992; Goff, 1997). Like pasteurization, it may have subsequently effects on physical properties of emulsion and its whipping aptitude. Aim of this work For the present study, we focused on effects of heat treatment and ageing time on ice-cream mix physical and whipping properties. Materials and Methods Analysis Methods Emulsion structural characteristics laser light scattering measurements (Malvern), rheological properties at 4°C, using a controlled stress rheometer (Carri-Med CSL100) equipped with a cone and plate geometry (ø=6 cm with 4° angle foaming properties (10 min whipping at 4°C) overrun whipped emulsion microstructure observations Ingredients Sugar ------------------------------------------------15% Non Fat Milk Solids-------------------------------10% Stabilizers / Emulsifiers--------------------------0.5% Anhydrous Milk Fat (AMF) or mixtures of Stearin and Olein fractions-----------------------10% Ice cream mix preparation in pilot scale ingredients blending in hot water and stirring (10 min-70°C) pasteurization upon heating (80°C), and hoding for 40 s or 120 s) homogenization (110 + 40 bar) quenching to 4°C ageing at 4°C, for 2 h or 24 h whipping for 10 min at 4°C Results Impact of Pasteurization holding time and ageing on Rheological Properties Ageing time (h) 2 24 Pasteurization holding time (s) 40 120 Fat globule size d(4,3) µm 1.8±0.1 2.0±0.2 2.0±0.1 2.5±0.1 Viscosity at 5 s-1 (Pa.s) 0.46±0.04 0.45±0.04 0.48±0.02 0.43±0.01 G’ at 0.05 Hz (Pa) 2.99±0.18 2.31±0.19 2.63±0.44 2.11±0.24 Whatever pasteurization holding time and/or ageing period, ice cream mixes showed: Shear thining and thixotropic behavior Not significant changes in the apparent viscosity at 5 s-1 Viscosity (shear rate ranging from 3 to 300 s-1 in 10 min up and down cycles). Bar= 400 µm 2 h 24 h 40 s 120 s Ageing time holding time Increasing in pasteurization holding time and/or ageing time, reduces air bubbles number and homogeneity of their size distribution Peux-tu ajouter des histogrammes d’analyse d’image? decrease by about 30% for increasing ageing time from 2 to 24 h decrease by approx 20% for 120 s pasteurization holding time at 80°C, compared to 40 s. Overrun of ice cream mixes prepared using 40 or 120 s holding time at 80°C following 2 or 24 hours ageing Viscoelastic (frequency range of 5 to 0.01 Hz Whatever pasteurization holding time and/or ageing period, ice cream mixes showed: Viscoelastic behavior with a higher elastic properties Decrease in elastic modulus upon raising of heat treatment time and ageing time Conclusion Stability of the emulsions, a slight decrease with pasteurization holding time and also ageing time. Emulsions rheology, reduction in mix elastic modulus with ageing time and pasteurization holding time, but without significant changes in apparent viscosity values. Also they showed pseudoplastic and thixotrapic behavior. Whipping ability (overrun), Raising of pasteurization holding time and ageing time reduced overrun, air bubble size number and their size distribution homogeneity, due probably to fat globule size increasing. These variations could be due to fat droplets structural organization parameters (fat crystallization and interfacial adsorption properties of proteins) (Bazmi et al., 2006c; Relkin et al., 2003) and to continuous phase structural properties (stabilizers/protein hydration and their interactions) in multiphasic dispersed systems (Bazmi et al., 2006a et 2006b). References Bazmi, A. and Relkin, R. (2006c) Thermal transitions and fat droplet stability in ice-cream model systems: Effect of milk fat fractions. 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(2003) Influence of thermal processing on the properties of dairy colloids. Current Opinion in Colloid and Interface Science, 8: 359-364. Relkin P., Sourdet S. and Fosseux P-Y. (2003) Effects of protein structure on crystallization behaviour of emulsified fats: A DSC study, J. American Oil Chemical Society, 80: 741-746. Olsen S. (1992) Ageing of ice cream mix. Scandinavian Dairy Information, 6: 63-65. Sourdet S., Relkin P. and César B. (2003) Effects of milk protein type and pre-heating on physical stability of whipped and frozen emulsions. Colloids and Surfaces B: Biointerfaces, 00: 1-10. 13th World Congress of Food Science & Technology 17-21 September 2006 – Nantes, France