Physical modification is simple, cheap and safe because it requires no chemicals or biological agents when compared to other methods of starch modification. It is more connected to the emerging concept of 'green chemistry' for environmentally friendly applications. Physical modification of starch can improve water solubility and reduce particle size. The methods involve the treatment of starch granules under different temperature/ moisture combinations, pressure, shear and irradiation. Physical modification also includes mechanical attrition to change the particle size of starch granules. Physical modification techniques are generally given preference as they do not involve any chemical treatment that can be harmful for human use. The broad classification of starch physical modification into those that are thermal and others that is non-thermal. The thermal processes involve the ones in which the starch granule structures are destroyed (all pre-gelatinization processes) and the ones in which the granules are preserved (hydrothermal processes: annealing and heat-moisture treatment). In disparity, non-thermal processes are the application of high pressure, sound, pulse electric field and irradiation to alter the physicochemical and functional properties of natives for better applications in the food and non-food industries.
Modification of starch is an ever evolving industry with numerous possibilities to generate novel starches which includes new functional and value added properties as demanded by the industry. This review aims to summarize the latest developments and recent knowledge regarding physically modified starches.
Keywords: Pre-gelatinization, Hydrothermal treatment, Annealing, Heat-moisture treatment, Non-thermal modification