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

Abstract

The thermal stability of P-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. P-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 P-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.

Thermal Denaturation of Collagen Analyzed by Isoconversional Method

“…Note that a decrease in the E a value with the extent of conversion is equivalent to its decrease with temperature, because a is proportional to T. Since the activation energy represents the slope of an Arrhenius plot, its decrease with T indicates that the plot should be bent upward. This type of nonlinearity is seen on closer inspection of Figure 3 and has been observed earlier in the Kissinger plots for denaturation of lactoglobulin [25][26][27] and whey proteins, [31] although the origins of the effect have not been discussed.…”

“…An application of the Friedman method to denaturation of the human hair keratin has been reported, [24] however the method has been used in a single heating rate (i.e., non-isoconversional) form. There are reports on using the Kissinger method to determine the activation energy for denaturation of lactoglobulin, [25][26][27][28][29][30] whey proteins, [31] and lactoferrin. [32] The method evaluates the activation energy from the shift in the DSC peak temperature, T p , with the heating rate, b i , as follows:…”

Ohmic heating of dairy fluids—effects of local electric field on temperature distribution

“…Fouling during heat treatment of dairy product is caused by thermal denaturation of β-lactoglobulin. [2,3] It is therefore important to know the temperature distribution in a heater or heat exchanger before a detailed study of fouling can be conducted. Bansal and Chen [4] investigated fouling of an ohmic heater device similar to the current device except that the AC frequency used was 50 Hz.…”

Calorimetric information about food and food constituents

“…Whereas the na tive-to-de natured change in the pro tein state is a co-op er a tive phe nom e non that is ac com panied by sig nif i cant heat up take, change in hy dro pho bic in ter ac tions dur ing protein ag gre ga tion is an exo ther mic pro cess (Privalov and Khechinashvili, 1974;Biliaderis, 1983;Hayakawa et al, 1996;Gotham et al, 1992). Al though very rare, an exo ther mic com po nent due to pro tein ag gre ga tion was ob served fol lowing en do ther mic un fold ing de na tur ation (Rossi and Schiraldi, 1992).…”