Physical and thermal characteristics of amaranth (Amaranthus hypochondriacus) protein nanoparticles affected by ultrasound time and microbial transglutaminase

In recent years, protein nanoparticles have been well considered in the production of Pickering emulsions and low-calorie foods, but few of them have been introduced. Therefore, finding new sources of nanoparticles and modifying their physical and thermal properties is very important. In this paper, the effect of various levels of microbial transglutaminase (mTG) (0–30 μg/g of sample) and ultrasound time (0–20 min) on properties of nanoparticles prepared with Amaranth Protein Isolate (API) were investigated and optimal levels were achieved by Response surface methodology. Based on the data analysis, ultrasound had a significant effect on tested properties, so that with an increase in ultrasound time, the particle size became smaller. Excluding Zeta potential, all nanoparticles properties were influenced by the interaction of ultrasound and mTG. The enzyme had a great impact (P < 0.001) on Nanoparticles characteristics except for Glass Transition Temperature. However, depending on enzyme content, changeable behaviors in particle size, particle size distribution and denaturation temperature were detected which is generally associated with the changes in the structure and formation of covalent bonds with the function of mTG. Scanning electron microscopy of FE-SEM showed spherically synthesized nanoparticles with a size between 53 to 155 nm. This seems to facilitate the use of ultrasound reaction between nanoparticles and biopolymer matrix. Consequently, the optimized levels of 16.7 min for ultrasound and 9.47 micg/g for mTG resulted in generating a product with the considered characteristics. This novel and edible amaranth-based Nanoparticles could be suggested for Pickering emulsion preparation.