Effect of Nanoreduction on Functional and Structural Properties of Resistant-Starch from Lotus Stem

This study characterizes the resistant starch (RS) and ball milled RS nanoparticles extracted from the stem of Nelunmbo nucifera, an underutilized aquatic plant. Starch (NS) was extracted from lotus stem and subjected to enzymatic digestion to isolate naturally present RS. The RS nanoparticles were produced via planetary ball milling carried out for 30 min (RS30), 60 min (RS60), and 90 min (RS90). The samples so obtained were characterized using dynamic light scattering (DLS), scanning electron microscopy (SEM), light microscopy, Fourier transform infra-spectroscopy (ATR-FTIR), X-ray diffraction (XRD), and differential scanning colorimeter (DSC). DLS revealed a hydrodynamic diameter of 12.05 μm, 6.7 μm, 543.11 nm, 378.65 and 123.12 nm, and a zeta potential of −12.63, −22.15, −28.79, −35.08, and −27.42 mV for NS, RS, RS30, RS60, and RS90, respectively. SEM displayed oval and smooth NS particles, irregular RS particles, and small and disintegrated RS nanoparticles. RS nanoparticles had significantly higher apparent amylose content, resistant starch content, hydration properties, light transmittance, freeze thaw stability, and viscoelasticity than RS and NS. Also, the expected glycemic index of RS was significantly lower (p < 0.05) than that of NS, whereas nanoreduction elevated the glycemic index values of RS. Thus, lotus stem shows potential to be a source for RS, which could be used as wall material in growing functional and pharmaceutical industries.