Preliminary results about a new method to optimize a spray dryer process for producing high quality milk powders from cow, goat and she-ass milk concentrates

As quality is a very important factor in milk powder produced by drying, the optimal process must protect both nutritional and sensorial properties. Although heat damage indices (namely die insolubility index (IINS), thermal damage (IDT), protein denatu-ration) could be used to evaluate the correct processing of milk, they are very time-consuming. Hence a chemical marker, like vitamin C, is proposed for rapid assessment of the overall damage to the quality of the produced milk powder. Trials were carried out on milk concentrates from cow, goat and she-ass so as to optimize the process performance of die spray dryer, for each kind of milk, at mree inlet temperatures (120, 150, 185 °C); the feed flow rate was set at 0.5 dm3/h with outlet air RH% in die range 10-40%; raw milk was concentrated using a low pressure evaporator until an average level of 23% dry matter was reached. As expected, die thermal damage of the milk powder increased as the inlet air temperature increased; the oudct powder RH% was 96-98% poorly correlated wiUi the mass flow rate of the concentrate inlet. Moreover, the destruction kinetic of vitamin C was found highly correlated widi die thermal damage to die milk powder. At 175 °C inlet air temperature the overall Uiermal treatment on die she-ass milk concentrate, which is very heat-sensitive due to its high lactose content, was "weak" (IDT<80) and the milk powder of "premium or extra" quality (IINS<1.25ml and lactic acid = 0.07% < 0.15% ADMI). The titratable acidity values are uncorrected wiUi die process air temperature but depend uniquely from die raw milk freshness.