Reducing Whey Syneresis in Yogurt by the Addition of a Thermolabile Variant of β-Lactoglobulin

The addition of a thermolabile variant of β-lactoglobulin A (BLG A) R40C/F82C to raw skim milk reduced whey syneresis in a set-type yogurt which was manufactured using a reduced processing temperature of 70°C. R40C/F82C BLG is a site-directed variant of BLG A that contains two additional free thiol groups. These cysteine residues have been positioned in a hydrophobic region distal to the free thiol at cysteine-121. The additional cysteine residues appear to confer a more open, less compact structure as compared to normal BLG A. The R40C/F82C BLG has been shown to form a much stronger gel network and its polymerization can be started at ≥ 70°C as compared to BLG A, which does not gel ≤ 85°C. Native and SDS polyacrylamide gel electrophoretic analyses showed that the aggregation of R40C/F82C BLG when heated at ≥70°C in a BLG-free skim milk background was due to both hydrophobic interactions and thiol/disulfide interchange. Yogurt was manufactured from raw skim milk containing 2% skim milk powder that was heated at 70°C or 85°C and then inoculated with a combination of Lactobacillus bulgaricus and Streptococcus thermophilus. The addition of 0.075% BLG A to the milk before heating at 70°C did not significantly reduce the whey separation. In contrast, the addition of increasing concentrations (up to 0.075%) of R40C/F82C BLG decreased whey separation as much as 83%. Furthermore, the addition of R40C/F82C BLG decreased the time for curd formation as compared to when equivalent amounts of BLG A were added.