Ultrasound researches of starch swelling in water

Abstract

A lot of different biologically active substances and additives are used in the modern nutrition. Modified starch has the status of food additives according to the Codex Alimentarius.
The application of different methods of native starch processing enables to alter its structure and properties significantly. One of these properties is hydrophilicity. Starches with modified hydrophilic properties form a large group of modified starches that tend to swell.
The composition of the feedstock, the physical structure of dried and powdered starch, particle size after grinding, its porosity, thickness of the dried film paste affect on the properties of starches to swell.
The aim of the research is to determine the optimal concentration of starch in water for the development of sustainable technologies of food concentrates of fast preparation, which are based on the extruded starch raw materials.
The object of the research is extruded potato and wheat starches.
Research was conducted at medium and high frequencies on ultrasound installation US-12-EM, which enables to measure the change of wave absorption depending on the concentration of the solvent.
Attenuation of sound waves during swelling of the extruded potato and wheat starches in water at 18 °C was investigated. Thus kinetics of the starch molecules swelling in water was traced. Amount of solvent (water) is changed from 20 to 4 mass fractions relatively to starch. The authors researched dependence of ultrasonic wave absorption on the concentration of starch in solution for determining the optimal ratio of solvent and starch.
Descending curve of ultrasonic wave absorption for solution of extruded potato starch can be divided into three zones. Zone III is characterized by the complete swelling of starch particles in water, which are in a suspended state considering its large number while their molecules are placed far apart from each other (value between starch and water is more than 1 : 16). Swelling particles begin to touch each other in zone II (the ratio is from 1 : 12 to 1 : 16), and grains begin to stick with each other due to the lack of solvent at high concentrations of starch in zone I (ratio less is from 1 : 12).
Similar areas for wheat starch were determined too. Zone of nonlinearity is in the range of concentrations that correspond to the optimal ratio between starch and water 1 : 15 and 1 : 18 respectively for solutions of potato and wheat starches. Thus using ultrasound research for swelling process of extruded products is appropriate to identify optimal concentration of starch in water.