Fundamental study of physical and biochemical alterations to casein micelles during milk evaporation and ultrafiltration
Year: 2013
Type: dissertation
Abstract: Casein represents 80% of the protein in milk, which is predominantly present in the form of hydrated colloidal assemblies known as casein micelles.It is one of the most important components in milk system that has significant influence on the properties of dairy products.It is also the main component of several highly value-added dairy products (such as milk protein concentrate (MPC) and milk protein isolate (MPI)).The objective of this work was to investigate the physico-chemical alterations of skim milk (specifically casein and casein micelles) during processing (evaporation and ultrafiltration) and to understand the processes at a fundamental level in order to determine the effect of the processing parameters on the properties of casein micelles and milk products to ultimately improve the efficiency of dairy processing.Evaporation in the dairy industry is used for concentrating products such as milk and whey while it is also used as a preliminary step to drying.Milk products intended for milk powder are normally concentrated to a final concentration of 40 -50 % total solids before going to the spray dryer.To reduce heat impact on the heat sensitive components in milk system, evaporation takes place under vacuum at relatively low temperature.In this study, skim milk was concentrated by vacuum evaporation to concentration 12 -45 % total solids content.The hydration, composition and size of the casein micelle were investigated.The results show that during evaporation, both inter and intra micelle water were removed from the milk system and preferentially the serum water.The alterations were rapidly reversible but not completely.Ultrafiltration is a process in which semi-permeable membranes are used to separate components in a fluid on the basis of size.It is widely used in the dairy industry for recovering, fractionating and concentrating proteins in milk process streams.In this study, skim milk was concentrated by ultrafiltration up to four folds at different processing temperatures.The changes of milk and caseins were discussed and different processing conditions were compared.Casein micelles and colloidal calcium phosphate are affected contemporaneously by the system temperature.A comprehensive physico-chemical investigation of the dynamic responses of casein micelles to changes in temperature was performed in the range ii 10 °C -40 °C in real time.The temperature effects on casein micelles were consistent with the results of the ultrafiltration processing at different temperature.Lactose is an important energy source in milk system, and it also regulates the water content of milk during secretion.In evaporation and UF concentration, micellar water behaved differently: the micelle hydration decreased during evaporation, whilst increased during UF concentration.Lactose is highly responsible for this difference, and the lactose effects on casein micelles were studied in this work.This study investigates the temperature dependent dynamics of casein micelles, and physico-chemical behaviours under different lactose concentrations, evaporation or ultrafiltration conditions.The results show that casein micelles and colloidal calcium phosphate (CCP) are dynamic entities which are significantly affected by processing.The results have important implications for improving milk processing in dairy industry.
Author: Zhe Liu
Language: English
Topic: Proteins in Food Systems
Subfield: Food Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2287768156