BURN-ON IN ULTRA-HIGH-TEMPERATURE PROCESSING OF MILK

Sangeeta Prakash (2007). BURN-ON IN ULTRA-HIGH-TEMPERATURE PROCESSING OF MILK PhD Thesis, School of Land, Crop and Food Sciences, The University of Queensland.

       
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Author Sangeeta Prakash
Thesis Title BURN-ON IN ULTRA-HIGH-TEMPERATURE PROCESSING OF MILK
School, Centre or Institute School of Land, Crop and Food Sciences
Institution The University of Queensland
Publication date 2007-08
Thesis type PhD Thesis
Supervisor Deeth, Hilton C.
Subjects 300000 Agricultural, Veterinary and Environmental Sciences
Formatted abstract During ultra-high-temperature (UHT) processing of milk, some material deposits on the hot walls of the heat exchanger. Such “burn-on” deposits limit the run-times for UHT plants because they impede the flow of milk and also decrease the heat transfer coefficient of the heat exchangers. Longer run-times would reduce the amount of cleaning, increase the throughput of milk through the plant in a given time and generally increase the efficiency and profitability of milk processing. Burn-on is an industry problem which is not well understood. Knowledge of the factors which both enhance and minimise burn-on will lead to a reduction in fouling deposits and therefore increase run¬times. A bench-top UHT plant capable of processing small quantities of milk has been developed and successfully used for studying fouling in various dairy fluids. The temperature of the milk in the pre-heating and sterilizer sections, and the milk flow rate were monitored to evaluate the overall heat transfer coefficient (OHTC).
Goats’ milk fouled the heat exchanger much faster than cows’ milk mainly due to the higher concentration of ionic calcium in goats’ milk. Goats’ milk fouled very quickly and run-times of the UHT plant were short. The use of sodium hexametaphosphate (SHMP), tri-sodium citrate (TSC) and cation exchange resins to reduce ionic calcium prior to UHT processing, increased the pH and alcohol stability of the milk and markedly increased the run-time of the UHT plant.
Pre-heating temperature of 65°C caused severe fouling; increasing the holding time to 25 s did not improve the run-time of the UHT plant that remained the same as with holding time of 5 s. Pre-heating at the higher temperature of 95°C for 25 s holding time combined with a high-heat temperature of 145°C increased the processing time of the bench-top UHT plant to the maximum.
The heat treatment given to the milk powder during its manufacturing determined its UHT processability. Milk reconstituted from low-and medium-heat skim milk powder when UHT processed fouled much quicker than milk reconstituted from high-heat skim
milk powder and whole milk powder mainly due to the higher concentration of native β-Lg.
Fouling becomes more severe as the total solids concentration increases in reconstituted skim milk mainly due to the higher native β-Lg content. Fouling of heat exchangers by reconstituted concentrated skim milk can be reduced by controlling the formation of the activated sulfhydryl group of β-Lg. Oxidizing the –SH group of β-Lg by addition of KIO3 reduced fouling and increased the processing time.
The amount and type of κ-carrageenan and sugar added to chocolate milk are critical to maintain its stability during UHT processing. Chocolate milk formulated from whole milk powder (12%), cocoa powder (1.5%), κ-carrageenan (0.03%) and sugar (7%) gave the best results with the longest processing time.


 
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