Releasing Fat in Whole Milk Powder during Fluidized Bed Drying

Abstract

Spray-dried whole milk powders have been produced to a high bulk-to-surface-free-fat ratio due to the susceptibility to oxidation of surface free fat. Processing spray-dried whole milk powders in a fluidized-bed crystallizer by hot and high humidity air can cause the release of bulk fat and increase both inner free and surface free fat. This research investigates the fat release and its migration to particle surfaces by two different mechanisms: a) fat melting due to high temperature processing in a fluidized -bed crystallizer so that liquid fat can diffuse outwards to the particle surfaces; b) fat release from the matrix due to lactose crystallization, causing component segregation and releasing molecular bonds. More free fat is preferable in some dairy-based processing, such as chocolate making, where cocoa butter could be substituted by milk fat to adjust the viscosity of chocolate paste and formulate good chocolate taste. This research shows the possibility of releasing more than 90% of the bulk fat to increase free fat (inner and surface) in 15 minutes processing time. Different temperatures and humidities (45°C and 78% RH) have been found to provide suitable conditions to release the bulk fat by crystallizing lactose in higher amount, as a form of inner free fat (preferentially) which is ready for further use, such as in chocolate industries. Meanwhile the released fat, as inner free fat, has less contact with oxygen than surface free fat and maintains the powder quality better. The changes in particle structure and fat release processes have also been studied during fluidized-bed drying of spray-dried whole milk powders that could improve the control and design of the drying process for milk powders.