The dominating effect of ionic strength on the heat-induced denaturation and aggregation of β-lactoglobulin in simulated milk ultrafiltrate

The denaturation/aggregation behaviour of heated (78 °C, 10 min) β-lactoglobulin (1%, w/w) was examined as a function of heating pH (5.0–7.0), in the presence of different salts. Heating β-lactoglobulin in the presence of calcium (5 mm) significantly increased the level of aggregated protein at most heating pH values, compared to heating in water or sodium chloride (100 mm). Heating β-lactoglobulin in the presence of calcium (5 mm) and phosphate (5 mm), resulted in similar denaturation levels in the pH range 5.0–5.8 as in the presence of calcium (5 mm) alone but reduced denaturation in the pH range 6.0–7.0, probably due to the formation of insoluble calcium phosphate. The addition of NaCl (100 mm) counteracted the aggregation promoting properties of the calcium and calcium/phosphate systems. Heating β-lg in a simulated milk ultrafiltrate solution was similar to heating in NaCl alone. This suggested that Ca2+ effects alone may not explain the heat-induced denaturation/aggregation behaviour of β-lactoglobulin in milk whey systems.