Different effects of radio frequency and heat block treatments on multi-scale structure and pasting properties of maize, potato, and pea starches

Radio frequency (RF) heating as a novel food processing technology holds potential for the modification of starch. To expand the practical application of starch, a 27.12 MHz RF heating and heat block (HB) systems were used and compared to process starches obtained from maize, potato, and pea. The temperature changes and heating uniformity with these two different heating methods were analyzed, and the effect of those two treatments on multi-scale structural and pasting properties of the three starches was investigated. Results showed that the heating uniformity index λ of samples ranged from 0.003 to 0.008, and there was no significant difference in heating uniformity between RF and HB treatments under the same conditions. Compared with the HB treatment, there were more cracks, larger pores, and more debris on the surface of RF treated potato, maize and pea starch granules. After RF treatment, the internal structure of starch was less compact and the crystal layer was thicker using small angle X-ray scattering. The degree of order values of starch increased significantly after RF and HB treatments based on Fourier transform infrared spectroscopy observations. The heating rate had a less pronounced effect than the heat methods on amylose content. A opposite trend, however, was found on pasting properties. RF heating resulted in nonthermal effects on the multi-scale structure of starch, which was significantly different from conventional HB methods. This study may provide a theoretical basis for better understanding thermal and nonthermal effects of RF treatments.