Processing sequence in ultrasound-coupled food protein modification: pH shifting, enzymatic hydrolysis, and glycation

Abstract

Ultrasound is increasingly being combined with other processing techniques to tailor the structure and functionality of food proteins. However, the outcome of these treatments depends not only on acoustic conditions and the coupled technique but also on the timing of ultrasound application. Existing reviews generally classify combined treatments by modification route or protein source, thereby leaving sequence-dependent mechanisms insufficiently addressed. This review treats the processing sequence as an independent design variable, focusing on pH shifting, enzymatic hydrolysis, and protein-carbohydrate glycation. It distinguishes among ultrasound pretreatment, simultaneous processing, and post-treatment according to when ultrasound is applied relative to the modification process. These temporal modes expose proteins to ultrasound at different stages of structural and chemical transformation, potentially altering subsequent molecular reorganization and functional and nutritional outcomes. Excessive acoustic or chemical exposure may instead promote fragmentation, oxidation, amino acid loss or modification, or reaggregation. Accordingly, the functional effects of a given sequence depend on how ultrasound-generated intermediates evolve during subsequent modification or assembly and should be evaluated alongside digestive and nutritional quality. Drawing on studies covering different proteins, modification strategies, and analytical methods, this review proposes the sequence–state–outcome framework as a conceptual perspective rather than a ranking of processing modes. Direct comparisons under matched acoustic energy and reaction extent remain scarce, limiting conclusions regarding sequence superiority. Future studies should compare ultrasound sequences under equivalent acoustic input and reaction extent, improve parameter reporting, and validate this framework in concentrated food matrices and continuous-flow systems.