Corn starch is modified with citric acid (2.5% w/w) in aqueous, alcoholic media and in solid solid reaction (dry heat condition without any solvent). Degree of substitution is similar for both treatments, independent of use of solvent but higher than for dry heated starch citrate. Apparent amylose content of all starch citrates is higher than for native starch. Molecular weight, as determined by triple detection size exclusion chromatography, also decreases, demonstrating hydrolysis of chains. As a consequence, starch citrate prepared using dry heating and ethanol, as compared to aqueous media, show drastic reduction in pasting viscosity. X-ray diffraction pattern and morphology of the produced starch granules remain unaltered in all three reaction types. Starch citrates prepared using solvent less reactions show similar characteristics as that of conventional hydrolysis performed using concentrated hydrochloric acid. However, the solid solid hydrolytic reaction process using citric acid is far more environmental friendly and less costly than typical conventional hydrolysis processes. The present study is not only useful for starch systems but more generally for studying reactions in, for example, gums and cellulose.

Moth bean (Vigna aconitifolia) starch is modified in its dry state (110 °C for 8 h, 14% moisture) using various ratios of organic acids (citric acid and stearic acid) in solvent free (solid–solid) reaction mode. Apparent amylose content is observed to increase in organic acid treated starches. Modified starches show lower swelling power than native starch. Scanning electron micrographs display rough granules surface for treated starches. Crystalline polymorphic pattern of moth bean starch is unaffected by organic acid treatment and dry heating. However, relative crystallinity increases after dry modification. Pasting properties indicate reduction following hydrolysis and loss of granular strength. Resistant starch (RS) content increases as an effect of the modification. This novel modification provides different functionality as compared to aqueous protocols and also provides a clean alternative to replace acid hydrolysis process with concentrated mineral acids.