Influence of emulsifiers on ice cream produced by conventional freezing and low-temperature extrusion processing

Ice cream at six different levels of emulsification was produced by freezing in a conventional scraped surface freezer and with a serial configuration of a conventional freezer followed by a low-temperature extruder. The aim was to examine the influence of emulsifiers on the process, since both emulsifier addition and low-temperature extrusion may have similar effects on promotion of colloidal structure in ice cream. Ice cream samples from both processes were analyzed for stiffness at draw, fat destabilization indices, melting performance, and microstructure. Low-temperature extrusion generally promoted enhanced fat destabilization, however, fat particle size and solvent extractable fat showed different dependencies on emulsification level from the two processing systems. Although solvent extractable fat reached high levels with increasing emulsification, fat particle size data suggested that fat agglomerate size was controlled by mechanical shearing. Significant difference between the two systems was seen also in the meltdown test, where melting rates for unemulsified and slightly emulsified mixes led to a very low melting rate and high shape retention in extruded ice cream. Scanning electron microscopy detected generally smaller air bubbles for extruded ice creams. Enhanced fat structuring around the air bubble and into the serum phase was also shown for unemulsified extruded samples. (C) 2000 Elsevier Science Ltd. All rights reserved.