b-Lactoglobulin Aggregates from Heating with Charged Cosolutes: Formation, Characterization and Foaming - Food Colloids: Self-Assembly and Material Science - page 178

Recently, the use of silica or latex particles with different surface properties
and degree of hydrophobicity was demonstrated to stabilize interfacial films
against disproportionation. 6,9-11 Proteins have been also demonstrated to
exhibit a barrier against interbubble gas diffusion. However, gas diffusion
stability of protein films has been found to be less effective, with values of 40-80
min for bubbles prepared from 0.05 wt.% protein solutions, as compared to
lifetimes up to 300 min or even longer for bubbles stabilized by silica particles
(0.08 wt.% solution) under similar conditions. 6,12
It has been further demonstrated 13-15 that foam stability can be significantly
enhanced upon formation of gel-like protein layers and incorporation of
protein aggregates or coacervates in the interfacial film. It was also found in
the past 13,16,17 that one possible way to improve foam functionality is by
thermal treatment. The pH and ionic strength play an important role in
controlling the formation of soluble and insoluble protein aggregates upon
heat treatment. During thermal treatment, free SH groups are activated,
surface charges are screened and protein aggregation and protein hydrophobi-
city increases. 18-21 Specifically tailored protein particles might therefore be used
to prevent gas diffusion between bubbles leading to disproportionation, film
thinning, bubble coalescence and film rupture. The aim of this study was to
attempt to establish a correlation between the surface properties of soluble
aggregates formed during heat treatment of b-lactoglobulin (b-LG) in the
presence of charged cosolutes and their ability to improve foam stability.
12.2 Materials and Methods
12.2.1 Materials
b-LG-enriched whey protein isolate (BioPure b-LG, lot JE002-8-922, 13-12-
2000) was obtained from Davisco Foods (Le Sueur, MN, USA). The composi-
tion of the powder (wet basis) was 89.7% protein, 8.85% moisture, fat ( o 1%),
lactose ( o 1%) and 1.36% ash (major ionic components were 0.079% Ca 21 ,
0.013% Mg 21 ,0.097%K 1 ,0.576%Na 1 ,0.05%Cl ). The following protein
profile was determined by RP-HPLC for major fractions: 12.9% a-lactalbumin
(a-LA), 35% b-LG A, 32.4% b-LG B, and 1.2% bovine serum albumin (BSA).
The amount of non-native protein in the powder was about 4% as measured at
201C from the ratio between total protein at pH 4.6 and 7. 17 Arginine HCl
(BioChemika, lot 431391/1) and GdnHCl (BioChemika, lot 450290/1) were
obtained from Fluka Chemie (Buchs, Switzerland). All other reagents were of
analytical or HPLC grade (Merck Darmstadt, Germany). Owing to the high
content of b-LG (467%) in the powder, the b-LG-enriched whey protein isolate
is mainly referred to here as b-LG or just 'protein', unless stated otherwise.
12.2.2 Sample Preparation
The protein dispersion was prepared by addition of b-LG powder to Millipore
water, stirring at 201C for 2 h, and storing for 12 h at 41C to allow complete