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 °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 °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 ºC 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 °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.