Nutritive properties of freshly prepared and stored evaporated milks manufactured by a normal commercial procedure or by reduced thermal processes in the presence of nisin

Abstract

SummaryFrom a batch of raw milk, evaporated milk was prepared commercially by 3 procedures:A, a normal commercial procedure involving holding the filled cans at a maximum temperature of 113 °C for 15 min;B, with nisin added and holding at a maximum temperature of 105 °C for 15 min;C, with nisin added and holding at a maximum temperature of 113 °C for 3 min. The content ofBvitamins in the raw and evaporated milks was measured microbiologically; the nutritive value of the proteins was determined in rat tests.In milkA, 83% of the vitamin B12, 38% of the vitamin B6and 20% of the thiamine were destroyed during processing. In milkB, the losses were 67, 30 and 19%, respectively, only the loss of vitamin B12being significantly lower than in milkA. In milkC, the losses were 67, 23 and 14%, respectively, each of them being significantly lower than in milkA. There was no further loss of thiamine on storage of the milks for 12 months at 4 °C, but at room temperature and at 37 °C further losses occurred in all the milks. Similarly, the vitamin B6activity of the milks decreased on storage, the loss being greatest at 37 °C, but also detectable at 4 °C. No change in the vitamin B12content occurred on storage, and no losses of biotin, nicotinic acid, pantothenic acid or riboflavin were detected during manufacture or storage of the evaporated milks.The biological value and true digestibility of the proteins of the evaporated milks were slightly lower than for the raw milk. Neither nisin treatment nor storage at room temperature for a year affected these characteristics.