The Effects of Substitution Degree in the Carboxymethylation of Jackfruit Seed Starch on Starch Digestibility

Starch from jackfruit seeds shows potential for use in food production processes with high starch content. Modification of jackfruit seed starch to increase the resistant starch content makes it a promising candidate for prebiotics in the food industry. Carboxymethylation can provide benefits for starch utilization in improving starch functional properties such as solubility, viscosity, and resistant starch content. This study chemically modified starch through carboxymethylation at different concentrations of sodium hydroxide to investigate the effect of carboxymethyl substitution on the digestible properties of the starch. Carboxymethylation exhibited a high degree of substitution from 0.28% to 0.57% as a function of the concentration of sodium hydroxide (5–10 wt%). The treatment enhanced the swelling, water solubility, and water/oil absorption. The resistant starch content increased from ~ 21 to ~ 39.67%. However, the high degree of substitution showed structural deformation of the starch granules with a decrease in crystallinity from about 35 to 1% by SEM and XRD. The degree of carboxymethyl substitution increased resistant starch content, reduced rapidly digestible starch, and had negligible impact on slowly digestible starch. Jackfruit seed starch treated with 10% by weight of NaOH was the optimal value that increased carboxymethyl substitution to 0.57% and resistant starch content to ~ 40%. This concentration was also optimal for the functional properties of starch with the highest values of swelling degree (~ 27 g/g), water solubility (~ 50%), freeze–thaw stability (~ 20% of syneresis after 4 freeze–thaw cycles), and oil and water absorption (150% of oil absorption and 180% of water absorption).