Sutter Sonia C, Buera María P, Elizalde Beatriz E
Departamento de Industrias, Facultad Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428 Ciudad Universitaria, Buenos Aires, Argentina.
Int J Pharm. 2007 Mar 6;332(1-2):45-54. doi: 10.1016/j.ijpharm.2006.09.023. Epub 2006 Sep 23.
The effects of addition of divalent cations and phosphate buffer on the degree of beta-carotene encapsulation in a mannitol matrix during freeze-drying were analyzed. The degradation rate of encapsulated beta-carotene as a function of % RH and its relationship with the physical state of the matrix during storage at 25 degrees C was also studied. The presence of phosphate salts significantly delayed mannitol crystallization at a highly satisfactory degree during freeze-drying and, consequently, the degree of beta-carotene encapsulation increased. This effect was maintained over quite long time during storage of the freeze-dried samples at 25 degrees C. Unavoidable local variations in water content during 3 years storage caused the decrease of T(g) values and made the crystallization degree to increase. The divalent cations showed a synergistic effect and also modified the kinetics of beta-carotene degradation during storage, increasing its stability. The mechanism of crystallization inhibition likely includes a change in hydrogen bond network or/and change in molecular mobility in the presence of divalent cations and phosphate anions. The degradation rate of beta-carotene in a mannitol/KH(2)PO(4) matrix increased as increasing % RH until a value at which the samples collapsed (75% RH), and then the degradation rate decreased. Collapse phenomena may affect diffusion of oxygen from the surface to the inside of the matrix and increase retention of beta-carotene. Surface color was not an appropriate indicator for beta-carotene degradation, because it was mostly dependent on the optical properties of the matrix, which changed with the degree of matrix hydration and collapse.
分析了在冷冻干燥过程中添加二价阳离子和磷酸盐缓冲液对甘露醇基质中β-胡萝卜素包封率的影响。还研究了包封的β-胡萝卜素降解速率与相对湿度百分比的函数关系及其在25℃储存期间与基质物理状态的关系。磷酸盐的存在在冷冻干燥过程中以非常令人满意的程度显著延迟了甘露醇的结晶，因此，β-胡萝卜素的包封率增加。在25℃储存冻干样品的相当长一段时间内，这种效果得以保持。在3年储存期间不可避免的局部水分变化导致玻璃化转变温度（Tg）值降低，并使结晶度增加。二价阳离子显示出协同效应，并且还改变了储存期间β-胡萝卜素的降解动力学，提高了其稳定性。结晶抑制机制可能包括在二价阳离子和磷酸根阴离子存在下氢键网络的变化或/和分子流动性的变化。在甘露醇/KH₂PO₄基质中，β-胡萝卜素的降解速率随着相对湿度百分比的增加而增加，直到样品塌陷时的值（75%相对湿度），然后降解速率降低。塌陷现象可能会影响氧气从基质表面向内部的扩散，并增加β-胡萝卜素的保留率。表面颜色不是β-胡萝卜素降解的合适指标，因为它主要取决于基质的光学性质，而光学性质会随着基质水合程度和塌陷程度而变化。
