Molecular mobility and oxygen permeability in amorphous β-lactoglobulin films

Abstract

OF THE DISSERTATIONOur overall objective is to understand how molecular mobility modulates diffusion rates and thus chemical reactivity in films made from amorphous β-lactoglobulin. The phosphorescence emission spectra and lifetimes of the triplet probe erythrosin B embedded in the β-Lg films provide measures of the modes, rates, and distribution of molecular mobility in the film, providing the molecular detail necessary to connect food quality and stability to molecular structure and mobility. The mobility contours generated from this research provided us with information about the onset temperature and level of molecular mobility required to support permeability of atmospheric oxygen. In β-Lgbased binary matrices, sugars (sucrose, trehalose, maltose), plasticizers (glycerol, sorbitol, maltitol and PEG-400), fatty acids (palmitic acid, caprylic acid) and protein (BSA) were selected to investigate how variations in composition influence the molecular mobility and oxygen permeability in amorphous β-Lg matrix. Further more complicated β-Lg -based ternary matrices (maltose and maltitol) and (PEG and sucrose) were generated inorder to gain a deeper understanding of edible films.iii In pure β-Lg films there was linear correlation between molecular mobility and oxygen permeability. Various additives showed different results with respect to mobility and permeability. The addition of sucrose, maltose, maltitol and trehalose greatly reduced the mobility and the permeability of the β-Lg matrix. Glycerol exhibited an antiplasticization effect and showed decreased mobility at a molar ratio of 1:1 glycerol/ β-Lg.PEG greatly enhanced the permeability of β-Lg matrix. Fatty acids palmitic acid and caprylic acid had a rigidification effect on the matrix with no change in permeability. We were able to detect dynamic synergies in β-Lg maltose and maltitol mixtures, whereby these sugar-polyol mixtures at equal ratios anti-plasticized the β-Lg matrix and at unequal ratios plasticized the matrix. The tertiary matrix comprising of β-Lg, PEG 400and sucrose brought about a substantial reduction in the permeability. A better understanding of the mobility in these complex matrices will help improve the effectiveness of β-Lg in barrier applications in real food systems.

Effect of gelatin on molecular mobility in amorphous sucrose detected by erythrosin B phosphorescence

“…46,47 This physical model is also consistent with extensive evidence from Ery B phosphorescence. Spectral heterogeneity in Ery B has been observed in a wide variety of amorphous sugars and sugar alcohols, 28,48,49 and globular and fibrous proteins, 37,50,51 indicating that dynamic site heterogeneity may be a characteristic feature of amorphous biomaterials.…”

Photophysical Probes of the Amorphous Solid State of Proteins

“…We have investigated the relation between matrix molecular mobility and oxygen permeability in five amorphous solid proteins: the globular bovine milk proteins α-lactalbumin, 41 β-lactoglobulin, 23 and serum albumin, 34 the fibrous porcine gelatin, 31 and the seed storage protein soy 11S glycinin. For all proteins, the triplet probe erythrosin B was dispersed in the amorphous protein film and matrix mobility and oxygen permeability were monitored using measurements of the Ery B phosphorescence intensity decays over a range of temperatures in the absence (under N 2 ) and presence (under air) of O 2 .…”

“…20,21 At this state of minimal perturbation, phosphorescence of Ery B emission is sensitive both to the motions of molecules in its immediate environment 19,20 and to the permeability of oxygen. 22,23 From the excited triplet state, a molecule can return to the ground singlet state either by emission of a photon (phosphorescence) or by one of two non-radiative pathways, matrix-induced deactivation or oxygen quenching. Matrix-induced quenching, in which the excited triplet state undergoes intersystem crossing to an isoenergetic highly excited vibrational state of the ground singlet state, is facilitated by the motions of nearby molecules in the matrix that dissipate the probe vibrational energy 24,25 ; this rate thus provides a measure of local matrix molecular mobility.…”

The effect of salts on molecular mobility in amorphous sucrose monitored by erythrosin B phosphorescence

“…Recently, site heterogeneity has been detected in amorphous solids composed of sugars and sugar alcohols 13,14,16 and both fibrous and globular proteins. 17,20,21 Variations in molecular mobility are of interest because they may be relevant to degradation processes including physical aging 49,50 and chemi- cal reactions such as Asp-Pro peptide bond cleavage in Physalaemin in freeze-dried and freeze-concentrated carbohydrates. 51 Lower values of b indicate that a broader distribution of lifetimes are required to fit the phosphorescence intensity decays.…”

“…[4][5][6][7][8][9][10][11][12] We have recently demonstrated that phosphorescence of erythrosin B (Ery B) provides a sensitive indicator of molecular mobility as well as dynamic site heterogeneity in amorphous sugars [13][14][15][16] and proteins. [17][18][19][20][21] Amorphous sucrose is involved in the protection of living organisms, seeds, and spores against stresses induced by desiccation; [22][23][24] it is also the major component responsible for the stability of many dried and frozen foods. Its ability to protect biomaterials from freeze-thaw damage and to provide long-term storage stability has attracted considerable attention in an effort to understand the mechanisms of this stabilization and to develop stable solid state formulations for long-term storage of the labile compounds in foods and pharmaceuticals.…”