Influence of Physical Treatments on the Potato Starch Granules Micro- and Ultrastructure

In this research, potato starch was subjected to physical treatments in order to analyse the changes at the micro- and ultrastructural levels and finally to identify the optimal conditions for disintegrating the starch granules. For the analysis, 10% aqueous solutions of potato starch were treated with a) microwaves; b) heat and c) heat combined with ultrasounds. For each treatment type, the duration was 5 minutes, excepting the microwave treatment, where the time was 1 and 5 minutes; heat power varied from 180W to 900W at the tests with microwave, temperature varied between 65C and 100oC in the thermal experiments and at the thermal analysis combined with ultrasounds temperature had values between 35oC and 85oC. The effect of these treatments was analysed using microscopic techniques (optical and scanning electron microscopy) in order to describe the morphological and micro- and ultrastructural modifications of the starch granules. Results indicated that the morphological and microstructural differences mostly depend on the chosen treatment and on the working conditions. The microwaves treatment was shown to be more effective on disintegrating the starch granule than the thermal action combined with ultrasounds or the thermal treatment alone. Starch granule was cracked at the heat power of 180W even after 1 minute of treatment; after 5 minutes, the gel-like structure was clearly formed for all the granules. Ultrasounds also modified the granule structure by cracking. High temperature (minimal 85oC) was essential for the propagation of ultrasounds or for the thermal treatment in order to assure the efficacy of the physical treatments on the granule. o