A structural study of the self-association of different starches in presence of bacterial cellulose fibrils.

A multi-analytical study was performed to analyse the effect of bacterial cellulose (BCF) on the self-association of starches with different amylose content (wheat, waxy-maize), assessing macrostructural properties (rheology, gel strength) and some nano and sub-nano level features (small and wide-angle X-ray scattering). Although pasting viscosities and G' were significantly increased by BCF in both starches, cellulose did not seem to promote the self-association of amylose in short-range retrogradation. A less elastic structure was reflected by a 2-3-fold increase in loss factor (G″/G') at the highest BCF concentration tested. This behavior agreed with the nano and sub-nano characterisation of the samples, which showed loss of starch lamellarity and incomplete full recovery of an ordered structure after storage at 4 °C for 24 h. The gel strength data could be explained by the contribution of BCF to the mechanical response of the sample. The information gained in this work is relevant for tuning the structure of tailored starch-cellulose composites.

Effect of physical state of gelatin-plasticizer based films on to the occurrence of Maillard reactions.

The aim of this study was to evaluate the occurrence of the Maillard reaction on gelatin-based films (bovine and salmon) in the glassy state, in mixtures with low molecular weight plasticizers (e.g. glycerol, glucose and trehalose) at different storage times. For testing, the gelatin-plasticizer films were stored under glassy conditions (Tg-10°C), previously determined by calorimetric tests. Studies under accelerated conditions (T ≫ Tg) were also developed. Color, opacity and browning index (Br) were evaluated by computer vision at all storage times. Results showed in samples stored under glassy conditions that the Maillard reaction did not occur, independent of gelatin origin and type of plasticizer. Changes in color stated by opacity and Br were only significant (p < 0.05) in gelatin-glucose systems under accelerated storage conditions. The inhibition of reaction in gelatin films in the glassy state was related to the well-known conditions of low molecular mobility of glassy matrices, but also with the non-Maillard reactive characteristics of glycerol and trehalose.