Microfiltration of skim milk: assessing serum protein removal from a mass balance and energy consumption perspective
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Date
2023
Authors
Subhir, Surabhi
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Publisher
University College Cork
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Abstract
Application of microfiltration (MF) to skim milk as a separation technology offers a valuable source of versatile milk protein ingredients. Optimization of the microfiltration process is crucial to ensure product quality, reduce costs and enhance filtration performance in the dairy factory. An extensive review of the literature has identified gaps relative to quantification of serum protein partition dynamics and the influence of process conditions on the separation efficiency, both from a total protein and energy perspective. The objective of this thesis was to investigate the impact of filtration conditions, using both ceramic and polymeric MF systems on subsequent serum protein (SP) removal, to provide a comprehensive mass and energy balance relative to milk component separation dynamics. Initial studies using ceramic MF carried out at 50°C at a volume concentration factor of 3 (VCF3), with two diafiltration steps, established a benchmark for subsequent studies in this thesis, providing a quantitative mass balance for fractionated milk protein components and estimating corresponding energy requirements in kW h kg-1 SP removed. This study identified inaccuracies associated with standard nitrogen fraction determination and non-casein nitrogen analysis in particular, as applied to dilute/concentrated streams leading to discrepancies in protein quantification. To address this, quantitative tests were combined with complementary qualitative methods like SDS-PAGE and HPLC to provide insights into partitioning of serum proteins, which comprise both whey and caseins. Subsequent studies focused on polymeric spiral wound MF technologies, which investigated the impact of operational parameters such as membrane configuration (in-series or in-parallel), trans-membrane pressure (TMP) in the range of 75 to 120 kPa, VCF and process temperature on serum protein permeation, energy efficiency and foulant accumulation dynamics. When comparing and contrasting ceramic to polymeric MF systems under similar operating conditions (50°C, VCF3), the ceramic MF system had higher flux and cumulative SP removal rates (46 L m-2 h-1 and 90.14%, respectively) compared to the polymeric MF system (22.2 L m-2 h-1 and 62.1%, respectively). However, the ceramic MF system also required higher energy in kW h kg−1 SP removed (12.2 vs. 1.23 kW h kg−1 SP). The MF retentates produced from cold and hot polymeric MF were utilized to create whey-depleted recombined cheese milk, which altered the resultant sweet whey streams, which were subjected to in-depth compositional analysis. Sweet whey derived from MF retentate based cheesemilk had lower concentrations of whey proteins compared to traditional cheese whey along with alterations in essential amino acid composition and, in particular, threonine.
Collectively, the observations and findings presented in this thesis contribute to the overall understanding of MF efficiency and quantification of fractionated milk proteins. This thesis has established a benchmark for optimizing the filtration performance of future milk protein ingredients produced by MF, providing insights into the impact of plant configuration and operating conditions on protein transmission rates, fouling behavior and energy requirements.
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Keywords
Skim milk microfiltration , Serum protein removal , Mass balance , Energy consumption
Citation
Subhir, S. 2023. Microfiltration of skim milk: assessing serum protein removal from a mass balance and energy consumption perspective. PhD Thesis, University College Cork.