Burvall A, Asp N G, Bosson A, San José C, Dahlqvist A
J Dairy Res. 1978 Oct;45(3):381-9. doi: 10.1017/s0022029900016605.
The retention of the protein nutritional value during storage of lactose-hydrolysed dried milk at different water activities (aw) was studied and compared with that of ordinary milk. In the lactose-hydrolysed milk biologically available lysine decreased much more rapidly than in the ordinary milk at all the different aw studied. Thus, at conditions normally accepted for ordinary dried milk (aw approximately 0.2; moisture approximately 4%) there was an available lysine loss in the hydrolysed milk of about 25% after 2 months and about 40% after 6-months storage at room temperature. This occurred without any visible browning. It is concluded that drying to very low aw (less than or equal to 0.11) is necessary to obtain good stability of the protein nutritional value (PNV) in lactose-hydrolysed milk. The drying, however, must be done so that losses in nutritional value are minimal during that process. It should also be noted that fat oxidation might be a problem at such low aw. A chemical method for available lysine assay (guanidination and assay of homoarginine) gave values in good agreement with the biological evaluations with rats.
研究了在不同水分活度（aw）下储存的乳糖水解奶粉中蛋白质营养价值的保留情况，并与普通奶粉进行了比较。在所有研究的不同水分活度下，乳糖水解奶粉中生物可利用赖氨酸的下降速度比普通奶粉快得多。因此，在普通奶粉通常接受的条件下（aw约为0.2；水分约为4%），在室温下储存2个月后，水解奶粉中可利用赖氨酸损失约25%，储存6个月后约为40%。这一过程中没有出现任何明显的褐变。得出结论，为了使乳糖水解奶粉中的蛋白质营养价值（PNV）具有良好的稳定性，必须将其干燥至非常低的水分活度（小于或等于0.11）。然而，干燥过程必须以营养价值损失最小为原则进行。还应注意的是，在如此低的水分活度下，脂肪氧化可能是一个问题。一种测定可利用赖氨酸的化学方法（胍基化和高精氨酸测定）所得结果与用大鼠进行的生物学评估结果高度一致。
