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Studies on protein standardisation of skim milk powder-based systems using milk ultrafiltration permeate and lactose
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Date
2024
Authors
Cusack, Maeve A.
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Publisher
University College Cork
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Abstract
The protein content of skim milk powder (SMP) is often standardised to achieve more consistent composition and functionality, whilst also ensuring the protein content of the powder product is as close as possible to the target. This requirement for protein standardisation arises largely from the changes in chemical composition of raw milk, as influenced by stage of lactation, breed of cow, genetics and also factors including diet and weather. To achieve standardisation, two standardising media are permitted to reduce the protein content of milk, i.e., lactose and milk permeate. When lactose or skim milk permeate are added, either in liquid (reconstituted) or powder form, they reduce the protein content by effectively diluting the protein present in the milk. The objectives of the work reported in this thesis were to develop an optimised standardisation process, focused in particular on the approaches used for reconstitution of the standardisation media, lactose and skim milk permeate powder, including the influences of temperature, mixing time and holding time (Chapter 2). Both powders were reconstituted at 50% total solids and the resultant dispersions were analysed for a range of parameters, including pH, viscosity, colour, sediment, conductivity and lactose crystallisation. Reconstitution of the skim milk permeate and lactose powders at 80°C, followed by cooling to 60°C, was determined to be the optimal process for
preparing the standardisation material, resulting in dispersions with low viscosity and low levels of sediment, when compared to those reconstituted at lower temperatures. This optimised standardisation process was then used in Chapter 3 to examine the influence of protein content modification and standardisation media on the functionality of low-protein skim-based systems, standardised with lactose or permeate to 3.3 and 3.5% protein, with unstandardised skim milk, with an average protein content of 3.92 ± 0.13% used as the control. These are considered low-protein skim-based systems as, when spray-dried, they produce powders with 16-22% protein, and do not meet the the Codex Alimentarius standard for SMP. The functionality of the low protein skim-based systems was investigated by measuring heat stability, particle size, viscosity and ethanol stability. The permeate-standardised skim milk systems had shorter heat coagulation times (<2 min) and increased particle size on heating from 45 to 85°C when compared to the lactose-standardised skim milk systems and unstandardised control. Mineral contents of the permeate-standardised systems were higher than those of the lactose-standardised skim milk systems. The results of this work clearly demonstrate that the additional minerals in the skim milk permeate systems strongly affected the functionality of the protein-standardised skim milk systems, particularly in applications involving high heat treatments. Rheological analysis showed minimal changes in viscosity on heating of all systems, indicating
that the systems were stable at 90°C for 2 min and could be used in lower heat-treated end applications. The original research described in this thesis contributes new scientific knowledge to the process of protein standardisation, as applied to SMP, and to our understanding of the effects of protein standardisation on functionality and applications of skim milk-based systems.
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Keywords
Standardisation , Permeate , Lactose , Skim milk , Milk powders , Protein , Skimmed milk powder
Citation
Cusack, M. A. 2024. Studies on protein standardisation of skim milk powder-based systems using milk ultrafiltration permeate and lactose. MSc Thesis, University College Cork.