Addition of galactomannans and citric acid in corn starch processed by extrusion: Retrogradation and resistant starch studies

Starch-galactomannan mixtures were elaborated by extrusion using a general factorial statistic design with three variables: galactomannan type (guar gum, tara gum and locust bean gum) at 10% (w/w), citric acid concentration (0-2.5% w/w) and storage time at 4 degrees C (0-7 days). Galactomannan type, citric acid concentration and storage time were factors that affected the physicochemical properties and microstructure of extrudates. Crystallinity of starch-guar gum extruded samples was higher compared with the samples obtained with the addition of the other gums and presented a variation from 3.38 +/- 0.16 to 6.68 +/- 0.23 when citric acid was added and stored at 4 degrees C and showed a correlation between long-range order (X-ray diffraction) and short-range order (FTIR). These results demonstrated the influence of the different galactomannans, the addition of citric acid and the storage at 4 degrees C of the samples, which resulted in an increase in the formation of V-type amorphous structures. The DSC analysis demonstrated the formation of amylose-lipid complexes in which transitions temperatures started at above 90 degrees C, these structures may slow retrogradation rates of samples. In addition, these complexes can act as a part of resistant starch found in samples, which varies from 4.64 +/- 0.15 to 12.13 +/- 0.30 g/100 g sample in different extrudates. Overall, galactomannan type, citric acid concentration and storage time were factors that significantly affected the properties and resistant starch content of extruded samples. (C) 2018 Elsevier Ltd. All rights reserved.