was isolated according to the procedures used by Simsek and EI \[[@pone.0150043.ref023]\]. Briefly, taro tubers were peeled, weighed, sliced, and ground in a commercial blender with triple weight of 0.1% NaOH solution. The slurry was centrifuged at 3500 g for 10 min. The sediment was suspended in water, neutralized with 0.1 N HCl solutions, and centrifuged again. The sediment was then suspended in 0.1 M NaCl solution, and 10% (v/v, based on the volume of 0.1 M NaCl) toluene was added. The solution was stirred overnight at room temperature. After standing for 1 h, the suspension separated into two layers. The bottom layer was centrifuged and the sediment starch was washed with distilled water to completely remove the NaCl, dehydrated with ethanol, and air-dried in an oven at 40°C. The content of the protein and fat in taro starch were 0.82% and 0.40%.

The SNPs were prepared following the method described by Dai et al. \[[@pone.0150043.ref003]\]. Taro starch slurry (15% w/v in pH 5.0 buffer solutions) was cooked in boiling water and stirred vigorously for 30 min. The cooked starch was cooled to 58°C and pullulanase (30 ASPU/g of dry starch) was added. After 8 h incubation period, the hydrolysate was centrifuged (3000 g, 5 min). The sediment was discarded and the supernatant was heated at 100°C for 10 min to stop the reaction; then, it was cooled to room temperature. The solution was stored at 4°C for 8 h to retrograde. The ensuing nanoparticles were washed several times with distilled water until neutrality was achieved and then freeze dried to obtain SNPs.

2.3 Preparation of OSA-SNPs {#sec005}
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SNPs (10 g, dry weight) were dispersed in 500 mL 50% ethanol with continuous stirring at 40°C in an ultrasonic cleaner (KQ-500B, Kunshan, China). Then, the SNPs suspension was maintained between pH 8 and 9 by adding NaOH aqueous solution (0.1 mol/L). Different amounts of OSA (50 or 100% based on the weight of the starch) were added (OSA diluted 5 times with absolute alcohol, v/v) slowly ov