COLLOIDAL ASPECTS OF ICE-CREAM - A REVIEW

Ice cream is a complex food colloid that consists of air bubbles, fat globules, ice crystals and an unfrozen serum phase. Ice crystals and a ir bubbles are usually in the range of 20-50 mu m. The air bubbles are usually partially coated with fat globules and the fat globules are c oated with a protein/emulsifier layer. The serum phase consists of the sugars and high molecular weight polysaccharides in a freeze-concentr ated solution. Various steps in the manufacturing process, including p asteurization, homogenization, ageing, freezing, and hardening, contri bute to the development of this structure. Proteins and emulsifiers co mpete for interfacial space during the homogenization of the fat and t he creation of the mix emulsion. Following homogenization, the emulsio n is further affected by changes occuring during the ageing step, viz. , crystallization of the fat and rearrangement of the fat globule memb rane to the lowest free energy state. This emulsion then undergoes bot h whipping and ice crystal formation during the dynamic freezing proce ss, which contributes to the development of the four main structural c omponents of the frozen product: a discontinuous foam, a network of pa rtially coalesced fat surrounding the air bubbles, ice crystals, and a continuous, freeze-concentrated, unfrozen aqueous solution. (C) 1997 Elsevier Science Ltd. All rights reserved.