The effects of glycerol on molecular mobility, oxygen diffusion and microstructure in amorphous zein matrix were studied using phosphorescence and atomic force microscopy (AFM). Films containing various amounts of glycerol (0, 5, 10, 20 and 30 wt%) were cast from solutions of 0.5% (w/v) zein in 70% ethanol/water (v/v). Erythrosin B (Ery B) phosphorescence was used to monitor the molecular mobility of these matrices over the temperature range from 0 to 100 degrees C. Analysis of Ery B emission peak frequency and bandwidth and intensity decay provided information about thermally-activated modes of molecular mobility in the matrices. Dipolar relaxation around the triplet state of Ery B was weakened and the extent of relaxation was decreased at low concentration glycerol (<= 10%), indicating a role as antiplasticizer. The rate of non-radiative decay from the Ery B triplet state indicated that glycerol only performed as a plasticizer and increased the local mobility of the zein matrix at and above similar to 20 wt %, while in films with glycerol at <= 20 wt % the local mobility remained nearly constant or only slightly increased compared with pure zein. Though transitioning from antiplasticizer to plasticizer at higher content, glycerol dramatically suppressed the oxygen permeability of the film in the whole concentration range tested. AFM images indicated that glycerol induced aggregation of zein complexes. These results indicate how the addition of glycerol to zein films could affect the physical properties, structure and thus functional properties in ways that influence their eventual use. (C) 2014 Elsevier Ltd. All rights reserved.

The effect of the addition of non-reducing sugars or methylcellulose on the matrix physical properties and rate of non-enzymatic browning (NBR) between exogenous glucose + lysine in a starch-based glassy matrix were studied, using the methods of luminescence and FTIR. Amorphous starch-based matrices were formulated by rapidly dehydrating potato starch gel mixed with additives at weight ratios of 7:93 (additive:starch). Data on the phosphorescence emission energy and lifetime from erythrosin B dispersed in the matrices indicated that sugars decreased starch matrix mobility in a Tg-dependent manner, except for trehalose that interacted with starch in a unique mode, while methylcellulose, the additive with the highest Tg, increased the molecular mobility. Using FTIR, we found that methylcellulose decreased the strength of hydrogen bond network and sugars enhanced the hydrogen bond strength in the order: trehalose > maltitol > sucrose. Comparing those changes with the rate of NBR between exogenous glucose + lysine, we suggest that NBR rates are primarily influenced by matrix mobility, which is modulated by the hydrogen bond network, and interactions among components.