Trapping of carvacrol by konjac glucomannan-potato starch gels: Stability from macroscopic to microscopic scale, using image processing

The aim of the study was to show that the presence of a small quantity of konjac glucomannan (KGM) in potato starch suspension increased the stability of carvacrol trapping. For that purpose, several freeze-thaw cycles were used to accelerate the ageing of the product and consequently drastically destabilize the gels, and induce syneresis. The stability of carvacrol trapping was evaluated by the quantification of carvacrol in the syneresis liquid. The stability of the starch gel structure was studied at microscopic and macroscopic scale. The moment of the addition of carvacrol and the presence of KGM both had an effect on the stability of carvacrol trapping and of the structure of the gel. KGM promoted amylose retrogradation but slowed down amylopectin retrogradation. The stability of potato starch gels can be improved by the addition of a small quantity of KGM which showed a `cryo-protectant' behaviour. New method to characterize the micro and macrostructure from SEM images processing has also been proposed. The processing of microscopy images was done using Generalized Fourier Descriptors and allowed the characterization of each sample. The carvacrol addition lowered the physical stability of the gel with larger pores and increased syneresis. On the contrary, the KGM addition increased the size of the pores but prevented the formation of very large pores and reduced syneresis. The most stable system was obtained by the addition of carvacrol at the end of heating, in a konjac glucomannan potato starch gel. (C) 2016 Elsevier Ltd. All rights reserved.