The development of the Maillard reaction in pasteurized, UHT and in-bottle sterilized dietetic milks was studied. In these products damage caused by heat
treatments could increase as a result either of the addition of various ingredients or
of manufacturing processes that alter their content of reducing carbohydrates.
Protein damage was evaluated by measuring furosine by reversed-phase ion-paired
HPLC. The levels of furosine detected made it possible to assess the amounts of
biologically unavailable lysine. In all milks analysed blocked lysine values were
<340–350 mg/g total lysine, the level at which lysine becomes the limiting amino
acid in milk. Pasteurized dietetic milks had levels of blocked lysine similar to that in
ordinary pasteurized cows' milk. In some UHT and in-bottle sterilized dietetic milks
their different composition resulted in an increase in the blocked lysine content. In
some in-bottle sterilized milks, protein damage greatly reduces the beneficial effects
of milk as a dietary supplement. Lactose-free milks, which are more susceptible to
protein deterioration because of their higher content of reducing carbohydrates, were
also analysed after storage at 20°C and at [les ]4°C. At the end of their recommended
storage times, they contained limited amounts of blocked lysine only if they had been
stored at [les ]4°C.