Gelling Characteristics of Emulsions Prepared with Modified Whey Protein by Multiple-Frequency Divergent Ultrasound at Different Ultrasonic Power and Frequency Mode

Abstract

The effect of ultrasonic frequency mode (mono, dual and tri-frequency) and ultrasonic power (0–300 W) on structural properties (intrinsic fluorescence and sulfhydryl content) of whey protein was studied. Emulsions prepared with modified whey protein were used to form the heat-set gels, and the properties of whey protein emulsion gels (WPEG) and their digestion were investigated. The textural and rheological properties of WPEG prepared using whey protein pretreated by mono and dual-frequency ultrasound at the power between 180–240 W were enhanced, while those of WPEG prepared with whey protein pretreated by triple-frequency above the power of 180 W were declined. WPEG prepared using whey protein pretreated by dual-frequency ultrasound (DFU) with the power of 240 W had the highest hardness and storage modulus which were 3.07 and 1.41 times higher than the control. The microstructure of WPEG prepared using DFU pretreated whey protein showed homogeneous and denser networks than those of the control according to the results of confocal laser scanning microscope (CLSM). The modification in the microstructure and properties of the WPEG prepared using DFU pretreated whey protein delayed the protein disintegration during the first 30 min of gastric digestion when compared with control. Whereas the release rate of free amino group of the WPEG prepared using whey protein modified by ultrasonic pretreatment increased during the intestinal phase when compared with that of control. The results indicated that using dual-frequency ultrasound to modify whey protein is more efficient in improving the properties of WPEG, and ultrasonic power should be considered during the application of ultrasound pretreatment in producing protein gels. The fine network of WPEG prepared with whey protein pretreated by ultrasound resulted in better hardness and storage modulus. Partially unfolding of the protein induced by ultrasound pretreatment might make the whey protein more susceptible to the digestive enzyme. Our results could provide new insights for using ultrasound as the potential processing tool on designing specific protein emulsion gels as the delivery system for nutrients.

Effect of Multi-mode Divergent Ultrasound Pretreatment on Hardness, Microstructure and Digestion of Acid-Induced Whey Protein Gels

“…Selected WP gels and control samples were digested using the INFOGEST method described by Minekus et al(2014) [40] with modifications as outlined in our previous work [35].…”

“…MFU, DFU, and TFU gels had little difference in hydrophobic bonds supporting the gel structure. The reason might be that MFU, DFU, and TFU treatment resulted in little difference in the whey protein tertiary structure, as revealed by intrinsic fluorescence [35].…”

“…On the contrary, the harder DFU and TFU WPG samples had a dense gel network with tiny pore sizes. The low porosity of the gel network might disturb pepsin diffusing into the protein aggregate interior, resulting in pepsin partitioning at the surface of protein aggregates [35]. It hindered the large boluses from enzymatic degradation, remaining the oral digesta in large size.…”

“…It hindered the large boluses from enzymatic degradation, remaining the oral digesta in large size. On the other hand, US treatment could improve the digestion of whey protein [35,36], and fragments in small sizes decreased fast in US samples. Since the gastric chyme not exceeding 1.4 mm was subjected to the intestinal phase, little solid particles existed in the intestinal digesta.…”

“…Studying the breakdown pattern of these US-treated proteins is expedient since the newly developed structure might affect digestion and nutrient release [5,34]. Our previous work showed that DFU pretreatment produced heat-induced whey protein emulsion gels with better mechanical properties and digestion than MFU [35,36]. However, the effect of multi-frequencies ultrasonic pretreatment on acid-induced whey protein gel's properties and digestion was unclear.…”