Shear effects on the properties and separation characteristics of whey protein precipitates

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dc.contributor.advisor Fitzpatrick, John J. Byrne, Edmond P. 2011-08-25T08:52:32Z 2011-08-25T08:52:32Z 2001-04 2001-05-01
dc.identifier.citation Byrne, E.P., 2001. Shear effects on the properties and separation characteristics of whey protein precipitates. PhD Thesis, University College Cork. en
dc.description.abstract Selective isoelectric whey protein precipitation and aggregation is carried out at laboratory scale in a standard configuration batch agitation vessel. Geometric scale-up of this operation is implemented on the basis of constant impeller power input per unit volume and subsequent clarification is achieved by high speed disc-stack centrifugation. Particle size and fractal geometry are important in achieving efficient separation while aggregates need to be strong enough to resist the more extreme levels of shear that are encountered during processing, for example through pumps, valves and at the centrifuge inlet zone. This study investigates how impeller agitation intensity and ageing time affect aggregate size, strength, fractal dimension and hindered settling rate at laboratory scale in order to determine conditions conducive for improved separation. Particle strength is measured by observing the effects of subjecting aggregates to moderate and high levels of process shear in a capillary rig and through a partially open ball-valve respectively. The protein precipitate yield is also investigated with respect to ageing time and impeller agitation intensity. A pilot scale study is undertaken to investigate scale-up and how agitation vessel shear affects centrifugal separation efficiency. Laboratory scale studies show that precipitates subject to higher impeller shear-rates during the addition of the precipitation agent are smaller but more compact than those subject to lower impeller agitation and are better able to resist turbulent breakage. They are thus more likely to provide a better feed for more efficient centrifugal separation. Protein precipitation yield improves significantly with ageing, and 50 minutes of ageing is required to obtain a 70 - 80% yield of α-lactalbumin. Geometric scale-up of the agitation vessel at constant power per unit volume results in aggregates of broadly similar size exhibiting similar trends but with some differences due to the absence of dynamic similarity due to longer circulation time and higher tip speed in the larger vessel. Disc stack centrifuge clarification efficiency curves show aggregates formed at higher shear-rates separate more efficiently, in accordance with laboratory scale projections. Exposure of aggregates to highly turbulent conditions, even for short exposure times, can lead to a large reduction in particle size. Thus, improving separation efficiencies can be achieved by the identification of high shear zones in a centrifugal process and the subsequent elimination or amelioration of such. en
dc.description.sponsorship Department of Agriculture, Fisheries and Food, Ireland (FIRM - Food Institutional Research Measure) en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2001, Edmond P. Byrne en
dc.rights.uri en
dc.subject Precipitation en
dc.subject Separation en
dc.subject.lcsh Whey en
dc.subject.lcsh Shear (Mechanics) en
dc.subject.lcsh Fractals en
dc.title Shear effects on the properties and separation characteristics of whey protein precipitates en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD (Engineering) en
dc.internal.availability Full text available en
dc.description.version Accepted Version en
dc.contributor.funder Department of Agriculture, Fisheries and Food, Ireland en
dc.description.status Not peer reviewed en Process & Chemical Engineering en

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© 2001, Edmond P. Byrne Except where otherwise noted, this item's license is described as © 2001, Edmond P. Byrne
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