The application of ohmic heating in lactose-free milk pasteurization in comparison with conventional heating, the metal contamination and the ice cream products

摘要

So far, there has been an increasing number of people with lactose intolerance. In this study, the lactose-free milk was prepared using lactase enzyme. The electrical conductivities of lactose-free milks were measured applying ohmic heating apparatus. Furthermore, the properties and metal contamination of milk samples pasteurized by conventional and ohmic method were compared while the fouling on the electrode surfaces were investigated. The normal milk and lactose-free milk were used for making ice cream. The main objectives were (1) to determine the potential of applying ohmic method in the pasteurization of lactose-free milk, (2) to investigate the metal contamination and fouling occurring when applying titanium and stainless steel electrodes for normal milk pasteurization and (3) to compare the properties of ice-cream manufactured from the pasteurized normal and lactose-free milks. It appeared that the electrical conductivities of lactose-free milk samples ranged between 0.592 and 1.320 S.m(-1) indicating that they could be efficiently heated by ohmic method. Less fouling occurred on the titanium electrodes than stainless steel electrodes. Normal milk pasteurized by ohmic method applying stainless steel electrodes contained rather high level of iron and chromium whereas milk pasteurized by conventional method and ohmic method using titanium electrodes contained safe level of chromium and none of iron. The melting rate of lactose-free ice cream was higher than that of the normal ice cream while the hardness of normal ice cream was higher.