Effects of heating modes and sources on nanostructure of gelatinized starch molecules using atomic force microscopy

Potato and corn starches were subjected to convective and microwave heating. The effects of microwave heating on nanostructure of starch molecules were studied by atomic force microscopy (AFM). Potato starches formed networks with the height from 0.3 to 11.0 nm under microwave radiation. Chains were observed dissociated from the networks with a nanoparticle head. Starch chains can be rod-like conformations or thinner linear structures on nanometer scale. Rod-like chains were about 1.0 nm in height, while the thinner chains were about 0.3 nm. However, corn starches did not show any networks under microwave processing. The capped chains of corn starches were similar to those of potato starches. The results revealed that microwave heating caused incomplete gelatinization of starch by comparison with convective heating. Heating modes influence the potato starch much than that on corn starch. The results can be applied on material selection for microwaved food development.