Changes in protein nutritional quality in fresh and recombined ultra high temperature treated milk during storage

The objective of this study was to determine the changes in nutritional qua lity of protein in stored UHT milk. Commercial fresh and recombined ultra h igh temperature (FUHT and RUHT respectively) treated milk samples were used . Pasteurized milk (P-milk) samples were used for comparison. Milk samples were freeze-dried for the use in diet formulation. Pasteurized milk samples were freeze-dried within 24 h of production. FUHT and RUHT milk samples we re freeze-dried after production (zero time), 3 and 6 months of storage at 37 degreesC. Three nitrogen balance experiments were done at zero time, aft er 3 and 6 months of storage. The diet used in all experiments were similar in composition except for protein source. In each experiment egg white (lo w protein), casein (control), P-milk, and either 0, 3 or 6 months old FUHT and RUHT milk samples were used as the source of protein in the diets. In e ach experiment 30 (six for each diet) mate Sprague-Dawley rats were used. A pparent digestibility (AD), true digestibility (TD), biological value (BV), and net protein utilization (NPU) were calculated for protein in casein an d all milk samples. The nutritional quality of protein in FUHT milk before storage was similar to that of protein in pasteurized milk, but it decrease d during storage for 3 months and then remained at the same quality up to 6 months of storage. BV and NPU of protein in FUHT milk after storage for 3 and 6 months were lower than that of protein in pasteurized milk by 4% (not significant) and 5% respectively. On the other hand, the nutritional quali ty of protein in RUHT milk before storage was lower than that of protein in pasteurized milk and remained at the same level after storage for 3 months : however, it decreased significantly after storage for 6 months. AD and TD , of protein in RUHT milk stored for 6 months were lower than that of prote in in pasteurized milk by 5% and BV and NPU were lower than that of protein in pasteurized milk by 9 and 12% respectively. The above reduction in nutr itional quality of protein in UHT milk may be of significant value in feedi ng young children who might be dependent on this type of milk in their diet .