STRUCTURAL-CHANGES IN OIL-IN-WATER EMULSIONS DURING THE MANUFACTURE OF ICE-CREAM

Ice cream was manufactured on a pilot plant and the product was analysed in terms of droplet size distribution and protein composition of the aqueous phase at three stages of the process: after homogenization, after aging and after freezing-aeration-hardening stages. The components (fat 8% wt, skim milk powder 8% wt, glucose syrup 40 DE 6% wt, sucrose 16.75% wt, stabilizer 0.45% wt) and water were homogenized using a two stage high pressure homogenizer (19 MPa + 3 MPa, 70 degrees C). The fat used was either butteroil or fresh unhomogenized milk cream. After an aging period (4 degrees C, 18 h), ice cream mixes were frozen and aerated using a continuous ice cream freezer (overrun = 100%, outlet temperature = -4 degrees C), hardened in a blast air hardening tunnel (-40 degrees C, 20 min) and stored (-30 degrees C). Droplet size measurements in homogenized and aged mixes did not show any influence of the type of fat used: fat globule distributions were monomodcal with an average surface/volume diameter d(32) similar or equal to 0.50 mu m. For both fats, the aging stage did not affect the initial droplet size distribution. The freezing-aeration-hardening stage led to a partial flocculation of aged mix, the effect being more pronounced in butteroil ice cream than in cream ice cream. Protein analysis carried out on the aqueous phase of butteroil ice cream showed a preferential adsorption of caseins over whey proteins during the homogenization stage. Aging and freezing-aeration-hardening stages gave rise to a partial desorption of the proteins from the surface of fat globules, especially during the freezing-aeration-hardening stage.