Karbowiak Thomas, Hervet Hubert, Léger Liliane, Champion Dominique, Debeaufort Frédéric, Voilley Andrée
ENSBANA-IMSAPS, Université de Bourgogne, 1 esplanade Erasme, F-21000 Dijon, France.
Biomacromolecules. 2006 Jun;7(6):2011-9. doi: 10.1021/bm060179r.
Translational diffusion of a fluorescein probe has been measured in iota-carrageenan edible films containing different amounts of glycerol (0, 15, 30, and 45%), using fluorescence recovery after photobleaching (FRAP) experiments. The effects of this plasticizer as well as the plasticizing effect of water on the diffusion of fluorescein have been studied in this edible coating mainly composed of natural biopolymer. Diffusion coefficients of about 10(-13) m2 s(-1) have been measured in these films for water activity (aw) lower than 0.7. Above this water content threshold, fluorescein translational diffusion coefficient increases up to 10(-12) m2 s(-1). Another interesting information obtained from FRAP experiments on this system is the ratio of the diffusing molecules which are immobilized in the carrageenan matrix at aw lower than 0.98. Moreover, films containing more than 30% glycerol (w/w carrageenan) present a huge increase of the diffusion coefficient of fluorescein at high water activity (about 2 orders of magnitude), this effect being less pronounced at low water activity. The increase of diffusion seems to be only related to the water content, and glycerol only acts through the enhancement of water adsorption. Therefore, in biopolymer films containing polyol plasticizers, the gain in mobility could be devoted to the effect of the ubiquitous plasticizing molecule, water, whose adsorption is increased by the plasticizer.
使用光漂白后荧光恢复（FRAP）实验，在含有不同量甘油（0%、15%、30%和45%）的ι-卡拉胶可食用薄膜中测量了荧光素探针的平移扩散。在这种主要由天然生物聚合物组成的可食用涂层中，研究了这种增塑剂以及水对荧光素扩散的增塑作用。在这些薄膜中，对于水分活度（aw）低于0.7的情况，已测量到扩散系数约为10^(-13) m² s^(-1)。高于此水分含量阈值时，荧光素平移扩散系数增加至10^(-12) m² s^(-1)。从该系统的FRAP实验中获得的另一个有趣信息是在水分活度低于0.98时固定在卡拉胶基质中的扩散分子的比例。此外，含有超过30%甘油（相对于卡拉胶重量）的薄膜在高水分活度下荧光素的扩散系数大幅增加（约2个数量级），这种效应在低水分活度下不太明显。扩散的增加似乎仅与水分含量有关，甘油仅通过增强水的吸附起作用。因此，在含有多元醇增塑剂的生物聚合物薄膜中，迁移率的增加可能归因于无处不在的增塑分子水的作用，增塑剂增加了水的吸附。
