Abstract
The effects of processing temperature on filtration performance and characteristics of retentates and permeates produced during ultrafiltration (UF) of skim milk at 5, 20, and 50 °C were investigated. The results indicate that despite higher flux at 50 °C, UF under these conditions resulted in greater fouling and rapid flux decline in comparison with 5 and 20 °C. The average casein micelle diameter was higher in retentate produced at 5 and 20 °C. The retentate analysed at 5 °C displayed higher viscosity and shear thinning behaviour as compared to retentate analysed at 20 and 50 °C. Greater permeation of calcium and phosphorus was observed at 5 and 20 °C in comparison with 50 °C, which was attributed to the inverse relationship between temperature and solubility of colloidal calcium phosphate. Permeation of α-lactalbumin was observed at all processing temperatures, with permeation of β-lactoglobulin also evident during UF at 50 °C. All UF retentates were shown to have plasmin activity, while lower activity was measured in retentate produced at 5 °C. The findings revealed that UF processing temperature influences the physicochemical, rheological, and biochemical properties of, and thereby govern the resulting quality and functionality of, retentate- and permeate-based dairy ingredients.
Highlights
Ultrafiltration (UF) has a wide range of applications in dairy processing, such as protein standardisation of cheese milk, production of liquid protein concentrates, high protein powders and novel milk products such as protein-enriched milk [1]
The results of this study show that UF of skim milk at 50 ◦ C resulted in higher permeate flux than
◦ C, higher processing which was to more membrane fouling at 50flux than at and the rate of flux decline during processing was considerably greater at as indicated by low permeability of clean water immediately post UF processing
Summary
Ultrafiltration (UF) has a wide range of applications in dairy processing, such as protein standardisation of cheese milk, production of liquid protein concentrates, high protein powders and novel milk products such as protein-enriched milk [1]. The choice of processing temperature strongly influences the entire UF process, and the structure and functionality of protein ingredients derived therefrom [2]. ≈50 ◦ C; low temperature UF at less than 15 ◦ C has become more widely adopted by the dairy industry in recent years [3,4,5]. The rise in demand for more natural and less processed products has paved the way for high-quality dairy protein ingredients for various premium food applications including clinical, sports, and infant nutrition. In the USA, the legal temperature requirement for on-farm UF of milk is
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