Lecture_9_milk_con - 1 Concentration by Evaporation in the Dairy Industry Carmen I Moraru Cornell University Concentration Why is it used Diminish

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Unformatted text preview: 1 Concentration by Evaporation in the Dairy Industry Carmen I. Moraru Cornell University Concentration Why is it used?- Diminish the volume- Enhance the shelf-life (osmotic pressure increases)- Concentrate certain components (i.e. lactose) Where is it applied?- Preliminary step before drying- Manufacturing of various dairy products (evaporated milk, sweetened condensed milk, concentrated yogurt) How can it be done?- Thermal evaporation of water- Freeze concentration- Membrane separation 2 Effects of concentration on milk components- Salt equilibria change Ca 2+ activity increases just slightly since calcium phosphate, which is saturated in milk, turns into un-dissolved state- Conformation of proteins changes due to changes in ionic strength, pH and salt equilibria change The tendency of protein molecules to associate and reach a compact conformation is increased - casein micelles coalesce- Some physico-chemical properties change Osmotic pressure increase, freezing point depression, boiling point elevation, electrical conductivity, density and refractive index increase Effects of concentration on milk components- Rheological properties are affected:- Viscosity increases - The product becomes non-Newtonian (viscoelastic and shear-thinning)- Water activity decreases- Hygroscopicity increases- Diffusion coefficients decrease due to reduced molecular mobility 3 Minimizing heating effects during evaporation- In order to allow boiling at lower temperatures (depression of boiling point) and reduce the negative effects of heat on milk, evaporation is always done under reduced pressure Figure: Vapor pressure of water vs. temperature (Walstra et al., 1999) Vapor pressure, Pa bar Temperature (C) How does evaporationtake place?- Heat is transferred from the heating medium (steam) to milk (food)- Upon absorption of latent heat of vaporization, water change phase from liquid to vapor- Vapors are removed from the surface of the boiling liquid/milk. The rate of evaporation is determined by: - the rate of heat transfer to the milk and - the rate of mass transfer of water vapor from the milk Steam Milk Vapor 4 Mass and heat transfer during evaporation Mass balance: Total mass balance: m initial = m conc....
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This note was uploaded on 05/02/2009 for the course FDSC 4250 taught by Professor Moraru during the Spring '09 term at Cornell University (Engineering School).

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Lecture_9_milk_con - 1 Concentration by Evaporation in the Dairy Industry Carmen I Moraru Cornell University Concentration Why is it used Diminish

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