Adaptation, optimization and control of processing spray-dried whole milk powder.

摘要

This study investigated the development, optimization and control of a process to produce a dry milk product that could be used for manufacture of various food products including milk chocolate and confections. The process involved exposing spray-dried whole milk powder to high shear and elevated temperature for a short time in a continuous mixer/processor. The three phases of the investigation included: (1) examining resultant changes in functional properties of whole milk powder; (2) determining the optimal processing conditions providing a desirable dry milk product for manufacture of milk chocolate; and (3) developing an intelligent control algorithm to produce a dry milk product with uniformly high quality.; The first phase of the research was focused on developing a paddle configuration inside the processor barrel and investigating the effects of process conditions on the resultant functional properties of whole milk powder. Response surface experiments were designed and samples were collected. Samples were analyzed to determine the free fat content, lactose crystallinity, particle size distribution, color, and moisture content. Exposure to elevated temperatures and high shear: (a) crystallized the lactose, (b) increased the free fat content to more than 80%, (c) altered the particle size distribution, and (d) reduced the average volume based particle size. The raw powder with creamy-white color turned into an oily paste with light-yellow color with the processing.; The second phase of the research was focused on determining the optimal processing conditions producing a dry milk product with desirable functional properties useful for the manufacture of milk chocolate. Lecithin was injected to the process to provide a stable system operation and to increase the capacity of the processor. Neural network and genetic algorithm searches were conducted on the data collected using two separate response surface experiments. For both of the designs, lecithin injection rate, processor screw speed, process temperature and powder feed rate were used as the control variables. The process conditions providing the highest free fat content (95.7%) were determined to be 27.2 kg/hr (60.0 lbs/hr) feed rate, 260 rpm screw speed, 100.5°C (213.0°F) process temperature, and 0.11 kg/hr (0.25 lbs/hr) lecithin rate.; The third phase of the research was focused on developing a real time fuzzy logic control algorithm for the whole milk powder processing system. The developed controller allowed the operator to set the desired color and desired power consumption values for the system operation. The controls of powder feed rate, processor screw speed and lecithin rate were accomplished using the error between the desired and actual power consumption, and the change in the actual power consumption over time. The error between the desired and actual product colors were used to determine the desired process temperature. The determined desired process temperature, then, was used as the target process temperature. The heater and cooling water electric valve on-times were determined based on the target process temperature. The controller performance was observed over time for 0.596 kW (0.8 hp) and 1.112 kW (1.5 hp) power consumption and 80, 85 and 90 color values indicating the ratios of the reflected intensities of red and near infrared colors (Red/NIR *100). The algorithm controlled the process at +/-0.074 kW (+/-0.1 hp) desired power consumption range and provided dry milk products with the desired color values within the +/-3.0 unit deviations. The free fat content was over 95% and lactose was in crystalline form in the produced dry milk product.