Development of Hydrodynamic Cavitation Assisted Functionalized Egg White Protein Hydrolysate Powder

Abstract

Proteins are key ingredients in food processing that govern both nutritional and functional behavior of food systems. They are macromolecules composed of amino acids linked together by peptide bonds. Being a macromolecule has its disadvantages in the human diet, such as longer digestibility and absorbability. Moreover, majority of food allergens reported are proteins. Significant efforts have been made to address this issue, and one of the major solutions explored was to hydrolyze the proteins. Protein hydrolysates are end products of hydrolysis of proteins obtained by enzymes, and acids or alkali that break down macromolecules into simpler structures. Recent research has largely focused on the modification of food proteins, to provide complete nutritional support to individuals who are incapable of digesting food. In this study, we have explored a novel approach to produce stable and functionalized protein hydrolysate powder from hen egg white. Egg white protein is well-known for its high-quality protein content; however, egg proteins have relatively low absorption rate in the human body (~3 g/h). Thus, producing hydrolysates can broaden their application in both textural and nutraceutical aspects. Moreover, hydrolysate powders are hygroscopic in nature when compared to native proteins which makes them unstable. Thus, the aim of this research is to develop a stable and commercially viable instant protein supplement. To intensify the hydrolysis process, a pre-treatment like hydrodynamic cavitation was employed to level up the production of amino acids and peptides. When compared to ultrasound the hydrodynamic cavitation as a pretreatment was beneficial in improving the functional, structural, and rheological properties of egg white proteins. Thus, an orifice plate hydrodynamic cavitator of 2 mm was utilized for pretreatment of egg white protein hydrolysate (EWPH) production. The obtained EWPH were evaluated for various physicochemical (degree of hydrolysis), functional (emulsifying, foaming), structural and nutritional properties (antioxidant activity and in-vitro digestibility). The egg white solutions (5% solid content) were pretreated for 10, 15 and 20 min with HC and later hydrolyzed using papain enzyme for 90 min. The structure analysis revealed that HC unfolded the protein structure confirmed through formation of β-sheet (from 15 to 46%) and loss of α-helix (34 to 14%) content with increasing treatment time. Through the exposure of hydrophobic bonds, the degree of hydrolysis and surface hydrophobicity increased which eventually improved the nutritional and functional properties of EWPH. The HC-15 min treated samples had the highest zeta potential (-25.4 mV) with lowest average particle size (346.5 nm) and denaturation temperature (70.67 °C) and with further increase in treatment time the stability of hydrolysates decreased. The study concluded that HC treatment can effectively improve the functional and nutritional properties of EWPH and a treatment time of 15 min is recommended for obtaining EWPH with improved properties. The stability of egg white protein hydrolysates was tested using a desugarization process. This process involves the removal of glucose, which can react with cephaeline, a phospholipid, and potentially affect the stability of the resulting protein hydrolysate powder. The desugared samples, especially those that underwent yeast fermentation, exhibited higher foaming and emulsifying abilities compared to the non-desugared samples. However, the desugarization process did not have a significant impact on the stability of the egg white protein hydrolysate powder. Thus, the protein hydrolysate powder was further studied by sorption isotherm analysis to understand the stability during storage and transport. EWPH obtained from two different drying methods namely freeze and vacuum drying, were assessed for their stability at elevated temperatures of 25, 35, 40, 45, and 55 °C. The sorption isotherms of EWPH were found to be a typical Type III sigmoid curve, representing a hygroscopic material. The EWPH samples had a steep increase in monolayer moisture content above 40% relative humidity. With respect to temperature, the samples had varied differences, were the vacuum dried samples when compared to the freeze dried samples had better stability. The HC treated samples did not have much variation with temperature. The DSC and XRD results confirmed that HC aided in improving the stability of freeze dried egg white protein hydrolysate powder. The study revealed that the HC treated freeze dried samples had the highest stability and functionality. An optimum storage temperature of 25 °C and relative humidity of 40% is suitable for maintaining the stability of EWPH powder. Overall, from the outcomes it can be suggested that the hydrodynamic cavitation technique provided a novel approach for developing stable egg white protein hydrolysate powder for producing nutrient-rich instant protein powder enriched with functional bioactive compounds and the process could be scaled up for large scale processing of protein powders.