Characterization of branched limit dextrin and impact on corn starch pasting properties

Abstract

Branched limit dextrins (BLDs) are composed of linear chains of alpha-(1,4)- d-glucose residues connected through alpha-(1,6)-linkages. In this work, BLDs were prepared by hydrolysis of starch by alpha- and beta-amylases and subsequent ethanol precipitation into fractions of different molecular weights and structures. The characterization of BLDs was done using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 1H nuclear magnetic resonance spectroscopy. The average molecular weights of BLDs from both corn and waxy corn starches decreased upon an increase in ethanol concentration from 70% to 90%, that is, from 1918.30 to 1274.23 and from 1938.11 to 1356.35, while the ratio of alpha-(1,4) to alpha-(1,6) glycosidic linkages increased from both corn (from 5.27 to 8.46) and waxy corn starches (from 3.80 to 4.62). The effect of BLDs with different degrees of polymerization on the pasting properties of corn starch was investigated by rapid visco-analysis (RVA). Confocal laser scanning microscopy (CLSM) observation of the BLD/cornstarch mixtures was also carried out to explore the possible interaction between corn starch and BLDs. RVA showed that BLDs significantly changed the viscosity parameters of the BLD/cornstarch mixtures. The results of CLSM observation of samples further indicate that the cornstarch and BLDs interacted in the cornstarch–BLD system because of the low molecular weight and mobility of BLDs.