β‐lactoglobulin denaturation and aggregation reactions and fouling deposit formation: a DSC study

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Summary The thermal stability of β‐lactoglobulin was studied using differential scanning calorimetry (DSC) as part of a larger investigation into milk and whey fouling. Measurement of kinetics using DSC is very difficult as the resultant trace is the sum of simultaneous denaturation and aggregational enthalpies; the two processes were demonstrated by measurements at different heating rates. β‐lactoglobulin denaturation proceeds via an intramolecular disulphide stabilized intermediate and is irreversible even before the denaturation temperature is reached. Denaturation and aggregational processes can be partially separated by measurements over a range of pH. The literature shows that the rate of fouling decreases as solution pH increases. However, DSC shows that the thermal stability of β‐lactoglobulin decreases as pH increases, particularly above pH 6. It is hypothesised that aggregation rather than denaturation might be the critical step in the formation of fouling deposit.