17E-4 |
|
N. D'CRUZ, Nutrition and Food Science, Auburn University, 328 Spidle Hall, Auburn, AL 36849 and L. N. Bell, Dept. of Nutrition & Food Science, Auburn Univ., 328 Spidle Hall, Auburn, AL 36849. The stability of proteins is paramount for their functionality. In protein-additive mixtures, the unfolding or denaturation temperature (Tm) has been shown to decrease as the additive glass transition temperature (Tg) decreased. However, the Tg of mixtures containing globular proteins was non-determinable and a link between Tg and Tm was merely hypothesized. Gelatin may be useful for studying the effect of plasticizers on protein unfolding because its fibrous nature enables the determination of Tg. The effect of food additives on the thermal stability of gelatin with respect to glass transition behavior was studied. A 20% (w/w) gelatin-water solution was freeze-dried, ground into a powder, and equilibrated at various relative humidities. Using DSC, Tm was determined from the initial scan and Tg from rescanning the sample. Gelatin solutions were also prepared containing glycerol, xylitol, sorbitol, sucrose, or trehalose, such that after freeze-drying the powder contained 10%, 20%, or 30% (w/w) of the polyol. Powders were stored over Drierite for 4-5 weeks prior to DSC analysis. Samples were analyzed minimally in triplicate. Moisture and polyols promoted a lowering of both Tm and Tg. This effect depended upon the additive type and concentration. When moisture increased from 2.4% to 19.8%, Tm decreased from 148.5±5.3șC to 52.4±1.2șC and Tg from 125.3±4.8șC to 12.6±3.1șC. Tm and Tg values decreased with increasing polyol concentrations. For example, 10% sucrose decreased Tm to 142.2±5.5șC and Tg to 108.8±7șC while 30% sucrose decreased Tm to 125.4±3.5șC and Tg to 85.9±7.9șC. For all the data, Tm>Tg, and a plot of Tm against Tg indicated a linear relationship (R2=0.95). These results suggest that formulations must be in the rubbery state for protein unfolding to occur. Plasticization by food additives affects the thermal stability of proteins, such as gelatin. This effect should be considered during product development to maintain protein functionality.
Session 17E, Food Chemistry: Proteins
|