Improved Heat Stability of Whey Protein Isolate by Glycation with Inulin

Yue He,Bongkosh Vardhanabhuti

doi:10.3390/dairy2010013

Abstract

Glycation between proteins and sugars via the Maillard reaction has been shown to improve the heat stability of proteins. In this study, inulin, a healthy dietary fiber, was glycated with whey protein isolate (WPI), and the effects of reaction conditions were investigated. Conjugates were prepared by freeze-drying mixed WPI and inulin solutions at 1:1 to 6:1 WPI-to-inulin weight ratios followed by dry heating at 70, 75, or 80 °C for 12 to 72 h under uncontrolled, 44%, or 80% relative humidity. Heat stability was evaluated by turbidity, particle size, and rheological measurements. Degree of glycation was assessed by quantifying the loss of amino groups and the formation of the Amadori compounds. Results showed that conjugation led to improved heat stability, as shown by decreased turbidity and particle size as well as the ability to maintain the viscosity compared to control samples. Based on the loss of amino groups, the optimum glycation conditions were achieved with WPI–inulin mixtures at 2:1, 4:1, and 6:1 weight ratios and 80 °C temperature for 12 to 72 h without controlling the relative humidity. The improved heat stability could be due to an increase in negative charge as well as increased structural stabilization of the proteins. Under a limited degree of glycation, glycated WPI–inulin conjugates have great potential to be utilized as food ingredients, especially in the beverage industry.

Highlights

The beverage market related to health and wellness has seen continuous growth in recent years, while the sale of carbonated soft drinks has experienced a decline since2004 [1,2]
Decreasing Whey protein isolate (WPI) to inulin ratio as well as increasing temperature and incubation time resulted in conjugates with increased heat stability and degree of browning, indicating a correlation between Maillard reaction and improved heat stability
The minimum dry-heating temperature was in agreement with the results reported by Oliver et al [27], which indicate that glycation between caseinate and inulin (1:1 weight ratio) was slow at 60 ◦ C and 80% relative humidity (RH)

Summary

Introduction

The beverage market related to health and wellness has seen continuous growth in recent years, while the sale of carbonated soft drinks has experienced a decline since2004 [1,2]. With increasing consumer demand for healthier food products, functional foods including high-protein beverages have seen a surge in sales [1]. Challenges in developing such products include the loss of heat stability (e.g., increased turbidity and the formation of sediments) at pH values near the isoelectric point (pI) of the protein and astringency at low pH (pH < 4.0). One major goal to improve protein functional properties is to increase the heat stability of the protein at pH values closer to the pI. In the propagation step, activated β-lactoglobulin molecules react with nonreactive β-lactoglobulin through thiol/disulfide exchange reaction, and build up the aggregates. Two active intermediates react and form a larger

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