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Sulfhydryl groups, which are buried in native β-lactoglobulin, were exposed 47 following irradiation and became available for quantification using the Ellman assay. 48The quantity of exposed sulfhydryls increased, but the number of total sulfhydryl 49 groups decreased. Gel permeation chromatography showed that some protein 50 aggregation occurred during irradiation. Fourier transform infrared (FTIR) 51 spectroscopy of irradiated β-lactoglobulin revealed changes in the secondary 52 structure, comparable to that of early events during heat-induced denaturation. There 53 was evidence for some photo-oxidation of tryptophan 54 55 56 57 58 59

The effectiveness of β-casein as a chaperone in the aggregation of whey proteins was investigated. β-Casein altered heat-induced aggregation as shown by a reduction in turbidity of β-lactoglobulin, α-lactalbumin, and bovine serum albumin (BSA) solutions. The pH of the mixtures greatly affected how much β-casein reduced the turbidity of the solutions; the maximum reductions in turbidity were observed at pH 6.0. Reducing the pH decreased the effectiveness of β-casein as a chaperone. An increase in ionic strength by the addition of NaCl or CaCl(2) also decreased the effectiveness of the chaperone. The addition of CaCl(2) had a larger effect than the addition of NaCl. The chaperone effect was seen at temperatures up to 145 °C. Differential scanning calorimetry (DSC) showed that β-casein did not alter the denaturation temperature of β-lactoglobulin. The kinetics curves for loss of native protein and turbidity development showed that β-casein did not function by slowing the aggregation process. It was concluded that β-casein competes with whey protein in the aggregate process and the aggregates formed in the presence of β-casein are smaller in size than those formed during whey protein self-aggregation. The formation of smaller aggregates gives rise to less turbid, more soluble protein solutions.

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