Spray-drying to improve the functionality of amaranth protein via ultrasonic-assisted Maillard conjugation with red seaweed polysaccharide

Abstract

Maillard conjugation has gained attention for its application in improving functional-properties of different plant proteins, including solubility and emulsification. Amaranth, a plant protein showing a higher lysine-content essential for conjugation, was conjugated with Gracilaria secundata polysaccharide via ultrasonic-assisted Maillard-conjugation. Post-ultrasonication, the outcomes from spray-drying as an alternative to freeze-drying were investigated. The comparison was based on conjugation-degree, solubility, water-or-oil holding capacity, and secondary structural changes in proteins. The protein: polysaccharide (w/w) of 1:1 and 2:1 displayed better conjugation, improved functional and structural aspects including the changes in the amide regions, oil-and-water holding capacity of the protein. Lower degree of conjugation, structural and functional changes for 1:2 samples can be the result of higher polysaccharide content leading to a shielding-effect over the reaction terminals of proteins. A significant difference between the properties was observed with different drying methods. Except for similar conjugation efficiency, the freeze-dried samples exhibited better oil-holding capacity, while the spray-dried samples performed better in water-holding capacity. The difference between spray-drying and freeze-drying could be due to the temperature difference resulting in protein denaturation, or the advancement of Maillard reaction. We demonstrated that spray-drying could be utilized as an alternative to freeze-drying step during ultrasonic-assisted Maillard conjugation, although a focus on optimization of conjugation and spray-drying parameters is required.