Physicochemical and functional characteristics of proteins treated by a pH‐shift process: a review

Abstract

Summary Advanced structures of food proteins are maintained by many forces such as hydrophobic activities, electrostatic interaction, and disulphide bond interaction, which can affect their functional characteristics to a certain extent. Therefore, many approaches have been utilised to improve functional characteristics of food proteins. pH‐shift process refers to the method that food proteins are treated under extreme alkaline or acid conditions followed by adjusting pH to isoelectric point or neutral pH. Many studies have showed that pH‐shift process can significantly affect the functional characteristics of food proteins, for example emulsifying activities, forming property, solubility and water/oil adsorption ability. pH‐shift process has been utilised to recover protein isolates from many sources including fish, fish by‐products, meat processing products. Many researches have indicated that the functional and physicochemical characteristics of recovered protein isolates are significantly influenced by pH‐shift process. In this paper, the latest studies regarding the functional and physicochemical characteristics of proteins treated or recovered through pH‐shift process, and potential applications of obtained protein isolates in the production of the hydrolysates or used as a delivery system were reviewed.

Protein Recovery of Tra Catfish (Pangasius hypophthalmus) Protein-Rich Side Streams by the pH-Shift Method

“…This may be due to the denaturation of proteins during harsh acid treatment. Denatured proteins will be lost in the sediment after the centrifugation of the extraction mixture [ 51 , 52 ]. The highest PER was obtained at pH 12 (95.3 ± 3.3%) ( p < 0.05).…”

Recovery of Functional Proteins from Pig Brain Using pH-Shift Processes

“…The effectiveness of the pH-shift approach to isolate protein from a variety of sources has been well-reported [ 11 , 12 , 13 , 14 , 15 ]. Isoelectric (pI) precipitation commonly follows protein solubilisation at the proper acid or alkaline pH to recover a functional protein isolate in the pH-shift process [ 15 ].…”

“…The pH-shift process, according to the findings, might be used to isolate protein from any source of protein. The pH-shift methodology has a number of benefits over typical recovery methods for extracting protein isolates from a variety of sources, including better yields, improved techno-functional properties, and greater impurity removal efficiencies [ 14 ]. Furthermore, no pH-shift-made protein isolate (PPI) from pig brain has been reported.…”

Profiles of sturgeon protein prepared by two methods and the correlation between protein fractions and functional properties

“…In addition, an increase of water‐soluble protein and decrease of salt‐soluble protein were observed with decreasing pH between SP pH2 and SP pH3 , which was not observed for Alkali‐pH proteins. This was due to the extreme acid conditions causing serious degradation of protein (Tang et al., 2021).…”

“…So far, the mainstream view is that the aforementioned differences are due to the diverse denaturation degrees of protein which can result from different preparation methods. Regarding various raw materials, protein with better functional properties can typically be obtained by Alkali‐pH than by Acid‐pH, and the relevant scholars have all attributed this to the more serious denaturation degree of protein in acidic conditions (Surasani, 2018; Shen et al., 2022; Tang et al., 2021). Furthermore, the extreme pHs used in pH‐shift result in a reduction in the functional properties of protein obtained, which has also mainly been explained by the more severe degree of denaturation under extreme conditions (Abdollahi & Undeland, 2019; Cha et al., 2020).…”