Chemical and physical changes resulting from UHT treatment of milk

A continuous flow, helically coiled tube, indirect heat exchanger was used to heat treat whole milk from 65.6 C to 148.9 C in 5.5 degree increments. Each total heat treatment consisted of 7 seconds. Samples of milk were taken at each heat treatment temperature. The serum was separated by rennin coagulation of the caseins and the heat denatured serum proteins.

A fluorometric method of analysis for total sulfhydryl content of milk serum was developed that was rapid and sensitive to changes in parts per billion. Quantitative changes in total sulfhydryl at the different ultra-high temperature (UHT) treatments were related to serum protein denaturation, and were used as an index to heat treatments.

Electrophoretic patterns of UHT treated milk showed that β-lactoglobulin was the most heat sensitive serum protein, and these patterns were used as an index to heat treatments. Alpha-lactalbumin was not denatured by the applied UHT treatments. The immunoglobulins were partly denatured, but a progressive increase in denaturation was not shown with increasing temperatures.

Comparisons of these results with earlier work showed that less milk serum protein was denatured by UHT treatments than by corresponding temperatures with 30 minute holding times.