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Improvement of Functional Properties of Whey Protein Isolate Through Glycation and Phosphorylation by Dry Heating

¹ Department of Biochemical Science and Technology, Faculty of Agriculture, Kagoshima University, Kagoshima 890-0065, Japan
² Food Technology Research Institute, Division of Research and Development, Meiji Dairies Corporation, 540 Naruda, Odawara, Kanagawa 250-0862, Japan

Corresponding author: T. Aoki; e-mail: aoki{at}chem.agri.kagoshima-u.ac.jp.

Whey protein isolate (WPI) was glycated with maltopentaose (MP) through the Maillard reaction, and the MP-conjugated WPI (MP-WPI) was then phosphorylated by dry heating in the presence of pyrophosphate. Glycation occurred efficiently, and the sugar content of WPI increased approximately 19.9% through the Maillard reaction. The phosphorylation of MP-WPI was enhanced with an increase in the dry-heating time from 1 to 5 d, and the phosphorus content of WPI increased approximately 1.05% by dry heating at pH 4.0 and 85°C for 5 d in the presence of pyrophosphate. The electrophoretic mobility of WPI increased with an increase in the phosphorylation level. The stability of WPI against heat-induced insolubility at pH 7.0 was improved by conjugation with MP alone, and further improved by phosphorylation. Although the emulsifying activity of WPI was barely affected by glycation and phosphorylation, the emulsifying stability of phosphorylated MP-WPI (5 d), was 2.2 times higher than that of MP-WPI. Gelling properties such as hardness, resiliency, and water-holding capacity of heat-induced WPI gel were markedly improved, and the gel was rendered transparent by phosphorylation. The calcium phosphate-solubilizing ability of WPI was enhanced by phosphorylation. These results suggested that phosphorylation by dry heating in the presence of pyrophosphate after conjugation with MP is a useful method for improving the functional properties of WPI.

Key Words: phosphorylation • whey protein isolate • Maillard reaction • functional property

Abbreviation key: C-WPI = control WPI, DH-WPI = WPI dry-heated in the absence of maltopentaose and pyrophosphate, EWP = egg white protein, MP = maltopentaose, MP-WPI = WPI conjugated with maltopentaose by Maillard reaction, Pi = inorganic phosphorus, PP-MP-WPI = phosphorylated MP-WPI by dry heating in the presence of pyrophosphate, WHC = water-holding capacity, WPI = whey protein isolate