32-9 |
|
S. GHOSH and J. N. Coupland. Dept. of Food Science, Pennsylvania State Univ., 126 Borland Lab., University Park, PA 16802 Instability of frozen food emulsions upon thawing is a major quality defect. Despite this, the mechanism of destabilization has not been thoroughly investigated. The goal here is to investigate the effects of simple sugars and aqueous protein composition on the stability of sodium caseinate-stabilized emulsions to freeze-thaw. Emulsions were prepared by homogenizing n-hexadecane (40 wt%) with sodium caseinate solution (2 wt%) to a mean diameter of 0.4 micron. Samples of emulsion were diluted in water and either sugar (glucose, fructose, trehalose, sucrose, maltose and corn syrup solids) or sodium caseinate solution to prepare samples with 5 to 40% oil and different amount of aqueous sugar and protein. Samples were then frozen at -20º C and thawed at 40º C before determining the free fat (i.e., emulsion destabilization) by solvent extraction. Small amounts of simple sugars dramatically decrease the freeze-thaw instability of the emulsions (such as from 33.7% for emulsion with no added sugar to 0.94% for 3 wt% added maltose). No significant differences were observed among the different types of sugars. A critical amount of unfrozen aqueous phase (3%) is necessary for the emulsion to be freeze-thaw stable. Emulsion stability also increased with aqueous protein content and above a critical value of 0.57 wt% aqueous protein, the emulsions were effectively freeze-thaw stable. The unfrozen aqueous portion in a frozen emulsion is a concentrated phase containing large amounts of dissolved sugar and protein essential to controlling the stability of the emulsion on thawing. Addition of sugar increases the amount of unfrozen water, which could form a hydration layer around the droplets sufficient to prevent interdroplet contacts under the pressure of the ice. Similarly, the presence of a critical aqueous protein content can also prevent droplet contact by forming a thick layer around the droplets in the freeze-concentrated emulsion and hence increasing the stability.
Session 32, Food Chemistry: Component interactions and processing effects
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |