FREEZE-THAW STABILITY OF KONJAC GLUCOMANNANE-POTATO STARCH GELS:STABILITY FROM MACROSCOPIC TO MICROSCOPIC SCALE, USING IMAGE PROCESSING

摘要

Freeze-thaw (FT) stability is often used to assess the ability of a gel to support the damage inducedbyfreezing; selected parameters such as drip loss, damage to structure etc can be used to assess thefreezetolerance of a gel. Konjac glucomannan (KGM) is a very specific hydrocolloid able to trap 100timesits weight in water; it has not been studied so far as an improver to enhance FT stability.The aim of the study was to show that the presence of a small quantity of konjac glucomannan (KGM)inpotato starch suspension increased the stability of carvacrol antioxidant trapping. FT cycles wereused toaccelerate the ageing of the product and to assess its stability. In addition to drip lossesdetermination, thestability of carvacrol trapping was evaluated by the quantification of carvacrol inthe syneresis liquid.Microscopic and macroscopic scales were considered with microscopy. Themoment of the addition ofcarvacrol and the presence of KGM both had an effect on the stability ofcarvacrol trapping and of thestructure of the gel. KGM promoted amylose retrogradation but sloweddown amylopectin retrogradation.The stability of potato starch gels can be improved by the additionof a small quantity of KGM, whichshowed a “cryoprotectant” behaviour. New method to characterizethe micro and macrostructure from SEMimages processing has also been proposed. The processing ofmicroscopy images was done using GeneralizedFourier Descriptors and allowed the characterizationof each sample. The carvacrol addition lowered thephysical stability of the gel with larger pores andincreased syneresis. On the contrary, the KGM additionincreased the size of the pores but preventedthe formation of very large pores and reduced syneresis. Themost stable system was obtained by theaddition of carvacrol at the end of heating, in a konjac glucomannanepotato starch gel.