Dairy Process Engineering

Module 6. Membrane processing

Lesson 31
EFFECT OF MILK CONSTITUENTS ON OPERATION OF MEMBRANE PROCESS

Introduction

The dairy industry has used membrane processing to clarify, concentrate and fractionate a variety of dairy products. Applying membrane technology to whey processing allowed the production of refined proteins and commercial usage and thus transformed a waste byproduct from cheese production into a valuable product. In addition to whey processing, membrane technology is also used for fluid milk processing with clear advantages. Further, specific milk components can be obtained without causing a phase change to the fluid milk by the addition of heat as in evaporation.

Membrane filtration technologies, such as ultrafiltration and reverse osmosis, are capable of the molecular fractionation of fluids. Milk is ideally suited for processing by membrane filtration because it is a fluid consisting largely of water, lactose, butterfat, and protein molecules. Separation at the molecular level means that butterfat, lactose, and protein can be isolated from one other.

Table 31.1

Component in Milk	Average Dimension (nm)
Water	0.2
Lactose	0.5
Casein Proteins	2.0-4.0
Fat	1,000-10,000

Reverse osmosis

RO appears to be a promising method for concentrating whey with significant savings in the total energy and overall cost. It has been suggested that RO can be used as a pre-concentration step for UF permeate to 20 percent, which would reduce the cost of transportation. The UF permeate containing approximately 4 per cent lactose and 1 per cent minerals can be concentrated to 18 per cent total solids by RO. From economic point of view, 2 fold concentration (i.e. 50 per cent volume reduction) of paneer whey and 2.5 fold concentration (i.e. 60 per cent volume reduction) of cow and buffalo cheese Whey.

UF

Fractionation of whey into protein rich and lactose containing streams is one of the most successful industrial applications of UF. Protein content of raw whey can be increased from an initial value of 0.6 per cent to over 20 per cent in the UF step. When whey is concentrated about 20 times by UF, a dry matter content of 18-20 per cent is attainable. It is suggested when UF of whey be carried out for deproteinization for lactose manufacture. Whey protein concentrates (WPC) are powders made by drying of retentate from ultrafiltration of whey. They are described in terms of protein content, percent protein in dry matter, ranging from 35 to 85 per cent. To make 35% protein product the liquid whey is concentrated to about 6-fold to an approximate total dry solids content of 9%.

Milk protein concentrate using ultrafiltration

· concentrating both casein and whey proteins

· Ratio similar to milk

Table 31.2 MPC composition

Components (% t/wt)	NFDM	MPC-56	MPC -75	MPC-80
Protein	35	56	75	80
Water	4	5	5	5
Fat	1	1.2	1.5	1.7
Lactose	51.3	31.7	10.9	5.5
Minerals	7.7	8.0	7.2	7.4

Microfiltration

MF can beused to remove large particles: casein fines, micro-organisms or microbial spores, fat globules, somatic cells, phospholipoproteins, particles, etc. from whey. MF separation process uses porous membranes with a cut off pore sizes in the Region of micron(10-6m)allowing passage of whey proteins but retaining fat globules, microorganisms and somatic cells. Whey usually contains small quantities of fat (in the form of small globules of 0.2 to 1micron) and casein (as fine particulates of 5 to 100micron).Centrifugal separation of whey does not completely remove the fat and casein fines. Thus, when the whey is ultrafiltered, these components can prevent the attainment of high purity, as well as having detrimental effects on the functional properties of WPC. MF can effectively remove substantial quantities of these undesirable components. Fat: protein ratios of 0.07 to 0.25 in whey can be reduced to 0.001 to 0.003 by MF. In addition some of the precipitated salts may be removed, and there is a considerable reduction in the microbial load. It is reported that 30 to 80 per cent residual lipids can be removed from cheddar cheese whey using MF. There is a 1.8 fold increase in the rate of UF of whey proteins when the lipids are removed by MF. When MF is performed on sweet whey as an intermediate step within the UF process, a fat content below 0.4 per cent in 85 per cent WPC powder can be achieved

Microfiltration of buttermilk

Factors Affecting Membrane Performance Fouling

Concentration polarisation

•Differential solute conc between membrane surface and bulk stream

•Reversibly affected by operation parameters

Fouling

•Formation of deposits

•Irreversibly affected by operation parameters

Membrane fouling

Two types

•Surface (temporary) fouling

•Pore (permanent) foul

Implications

•Higher energy consumption

•Frequent need for cleaning

•Affects membrane durability

•Effect on properties and quality of concentrate

•Overall economy of the membrane process

Surface (temporary) fouling

•Foulant appears an evenly deposited layer on the membrane surface

•Can be easily removed by cleaning solution

•Permeation rate of membrane can be regenerated by cleaning

•Most common type of fouling in UF plant

Pore (permanent) fouling

•Particulate matter diffuses into the membrane

•Could be caused by the poor quality of the cleaning water

•Uneven distribution of the foulant and compression of the separation zone

•Flux cannot be regenerated by cleaning

•Determines the lifetime of the membrane