pH and Heat Treatment Effects on Foaming of Whey Protein isolate

Abstract

TurbidityThe overrun obtained by whipping whey protein isolate (WPI) was significantly (~~0.05) affected by changing pH. Heating WPI at pH 4.0 reduced rate and amount of overrun. The highest overrun values for unheated WPI were observed at pH 5.0 and 7.0 after heating at 55°C for 10 min. The maximum foam stability for unheated WPI was obtained at pH 5.0. Heat treatment had little effect on stability at pH 4.0 or 7.0 but at pH 5.0, 80°C for 10 min improved stability by 65%. Based on surface pressure data, the rate of adsorption of P-lactoglobulin interfacial films and the work of compression correlated with overrun, maximum overrun, overrun development and foam stability.Before whipping, the aggregation of whey protein isolate after pH adjustment was determined by transmittance at 500 nm using a Spectronic 700 spectrometer (Bausch and Lomb, Rochester, NY). The values were expressed as Tb = (l-T500) x 100. A value of 100 corresponded to a completely turbid solution (0 transmittance). Foaming propertiesThe effects of pH and heat treatment on the foaming properties of WPI were assessed using the method of Phillips et al. (l-987): Overrun was measured (3 replicates) using 75 mL whey protein isolate (5.0% w/w) solubilized for 30 min with adjustment to the appropriate pH (4.0; 5.0 or 7.0) using either O.lN HeI or O.lN NaOH.'Th&soluti&s were held for 10 min at 25, 55 or 80°C: cooled to 25°C in a water bath (10 min) then whipped-for 5-min iniervals for a total of 20 min using a Sunbeam Mixmaster mixer (Sunbeam Corporation, Oak Brook, IL.). The amount of air incorporated was measured and recorded as Hoshino, T. and Yukawa, H. 1977. Effect of ultrasonic waves on heat trans-

Effect of foaming temperature and varying time/temperature-conditions of pre-heating on the foaming properties of skimmed milk

“…However, the decrease in foam density is due to increasing surface activity that is a result of the heat-induced partial unfolding of globular whey proteins. The partial unfolding of globular proteins by heat treatment leads to the exposure of reactive functional groups, resulting in increased hydrophobicity and flexibility as well as surface activity (Bals & Kulozik, 2003;Graham & Phillips, 1976;Jelen & Rattray, 1995;Phillips, Schulman, & Kinsella, 1990;Zayas, 1997). In Table 3, the contents of the acid soluble, nondenatured whey proteins (mg 100 À1 g) of skimmed milk and the foams produced after 20 min drainage, in relation to the .…”

Protein distribution at air interfaces in dairy foams and ice cream as affected by casein dissociation and emulsifiers

“…Caseins in dissociated form and a-lactalbumin in molten globular state are thought to be much more surface-active than in their native states (Lorient, Closs, & Courthaudon, 1989;Berliner, Meinholtz, Hirai, Musci, & Thompson, 1991;Matsumura, Mitsui, Dickinson, & Mori, 1994;Dalgleish, Goff, Brun, & Luan, 2002). Also, the influence of ions in solution on the foamability of protein is considerable (Phillips et al, 1990;Zhang et al, 2003). Ions were introduced to protein solutions along with chelating agents, e.g., Na + in Na 2 H 2 EDTA.…”

“…A large number of studies have been carried out to examine the foaming behavior of proteins under a variety of conditions. Factors such as heat treatment, pH and ionic environment influence the foaming properties of milk proteins (Phillips, Schulman, & Kinsella, 1990;Phillips, Yang, & Kinsella, 1991;Zhu & Damodaran, 1994;Patino, Delgado, & Fern! andez, 1995;Dickinson & Izgi, 1996;Ward, Goddard, Augustin, & McKinnon, 1997;Hagolle, Relkin, Popineau, & Bertrand, 2000).…”

Influence of heat and pH on structure and conformation of whey proteins

“…An observed improvement in overrun and stability of foams of 63 WP suspensions at pH 7 when heated to 55 ºC was attributed to denaturation of WP. It was 64 also observed that the availability of proteins to form films and emulsions decreased at higher 65 temperatures, in turn impairing foaming and emulsifying characteristics of the proteins 66 (Phillips, Schulman, & Kinsella, 1990). Denatured dispersions of randomly coiled molecules 67 of proteins have been reported to have greater viscosity than solutions of compact folded 68 globular molecules of the same molecular weight (Damodaran, 2008).…”