Production and properties of resistant maltodextrin from cassava starch

Abstract

This research aimed to determine the effects of processing conditions on molecular structure and selected properties of cassava-derived resistant dextrins (RDs) and resistant maltodextrins (RMDs). Cassava starch was mixed with hydrochloric acid solution to obtain the final acid concentration of 0.04-0.10% dry starch basis, dried at 50oC until having <5% moisture, and dextrinized at 100-120oC for 60-180 min. As acid concentration, heating temperature and time increased, water solubility, reducing sugar content, total dietary fiber (TDF) content and proportion of high molecular weight fiber fraction of RDs increased while their whiteness decreased. For the solution containing RDs produced under mild conditions (0.04-0.08% HCl, 100°C, 60 min), an endothermic peak at 45-70oC, having enthalpy of 1.66-2.14 J/g was detected. However, no endotherm was detected from the solution of RDs processed under extreme conditions. Harsher dextrinization conditions resulted in the RDs with slightly higher molecular weight but containing shorter branched chains. Dextrinization resulted in the formation of α-1,2, α-1,6, β-1,2, β-1,4 and β-1,6 in RDs. Lower proportion of α-1,4 linkage and α-/β-reducing ends with higher proportion of β-1,2, β-1,4, α-/β-1,6 linkages and degree of branching (DB) were found in RDs prepared under stronger dextrinization conditions. Although indigestible portion was enhanced by dextrinization, TDF of the RDs were only 7-47%. To increase the TDF content, RDs prepared from 5 different conditions (0.04% and 0.06% HCl, 120oC, 60-180 min), having >30% TDF, were selected for RMD production. The 30% RD solutions were treated with commercial α-amylase enzyme at 70oC, pH 6, for 90 and 120 min, to obtain the final dextrose equivalent of 8 and 12, respectively. The samples were then purified and spray dried. Alpha-amylase treatment produced RMD with shorter branched chains, lower molecular weight and glass transition temperature of maximally freeze-concentrated unfrozen phase (Tg’), but having higher TDF content, low molecular weight dietary fiber (LMWDF) content and unfrozen water content, comparing to its RD counterpart. RMDs had higher proportion of all β-glycosidic linkages, DB and α-/β-reducing ends than RDs. It was also found that RMDs with higher proportion of shorter branched chains (DP < 5) and LMWDF fraction, but having lower DB, had higher prebiotic activity score.