Dairy Process Engineering

Module 6. Membrane Processing

Lesson 30
ULTRA FILTRATION OF MILK

Introduction

Membrane filtration is a separation process which separates a liquid into two streams by means of a semi-permeable membrane. The two streams are referred to as retentate and permeate. By using membranes with different pore sizes, it is possible to separate specific components of milk and whey. Depending on the application in question, the specified components are either concentrated or removed/reduced.

Ultra Filtration of Milk

● Commercial membranes of UF have nominal weight cut-offs at 20,000 – 25,000.
● The protein and fat are retained in the retentate. Lactose, minerals and vitamins are fractioned between the retentate and the permeate.
● Minerals such as Ca, Mg, P and citrate are partly bounded to protein in milk and partly in solution. During UF, the former portion is retained and concentrated and the latter part passes to the retentate.
● Rejection coefficient of the components in whole milk

Total solids – 54%

Protein – 93 %

Fat – 100 %

Lactose – 0 %

Ash – 29 %

NPN – 62 %

● If during UF, if flux reduces to almost zero because of increase in protein concentration, diafiltration is followed.
● UF milk is useful in formulating reduced- or no-lactose dairy products.

1. Milk protein standardization and fractionation

● UF milk fractionated components can be used to stand the nutritional value of consumer milk or to prepare standardized milk powders, overcoming natural variations in milk composition.

● Increasing the protein content by ultrafiltration makes the milk whiter, and more viscous, the sensory quality more similar to that of higher fat milks.

● An MF/UF process can be used to fractionate non-fat milk into value-added protein ingredients. Resulting ingredients include native casein concentrates (from the retentate), pure milk serum proteins (from the permeate) and individual milk protein isolates that have application as emulsifiers, fortifying proteins and gelling agents.

2. Fermented dairy products

● UF can be used to standardize protein and total solids in milk for use in fermented dairy foods such as cream cheese, yogurt and cottage cheese.

● Fermented products made with UF milk have superior quality and sensory characteristics compared to products made from milk concentrated by conventional methods.

● Membrane filtration helps control quality attributes such as consistency, post-processing acidification and extent of syneresis.

● However, using membrane-processed milk often requires an adjustment in starter culture selection and fermentation conditions.

3. Cheesemaking

● The cheese industry uses membrane concentrated milk to elevate the solids level of cheesemilk.

● Future applications for membrane processing may include the manufacture of fresh, soft, hard and semi-hard cheese varieties.

● UF concentrated milk, with its fat and protein content concentrated to 3.5X, and a portion of the lactose, ash and water removed, possesses the ideal composition for the potential manufacture of fresh cheeses like ricotta or brine cheeses like Feta.

● Replacing 10-15% of the cheese milk volume with UF milk creates the opportunity to boost total solids, therefore increasing cheese throughput in factory by as much as 18%— subsequently reducing production costs.

● Using concentrated milk could also reduce rennet and starter culture requirements, depending on the application.

● In addition, using UF milk could reduce a cheese plant’s wastewater processing costs.

4. Cream

● Scurlock in 1986 used UF as the 1^st stage in the preparation of protein enriched whipping creams. Whole milk concentrated 2 to 5 fold by UF was separated conventionally to produce protein enriched creamswith fat 25 – 45 % (w/w).

5. Skim milk retentate powder

● Ultra filtered skim milk retentate is spray dried to obtain S.M. retentate powder with 50 – 65 % protein. It shows lower bacterial counts and acidity and an excellent flavour.

● A standardization of the protein levels with WMP with 32 – 35 % protein and skim milk powders with 38 – 41 % protein can be done by using UF skim milk and whey retentates and permeates.

6. Low lactose milk powder

● It is developed by using low lactose milk powder, lactose content of which can be reduced by 86 %.

● Lactose was replaced by malto-dextrin.

● Na and K salts are added to compensate the loss of milk salts.

7. Skim milk based concentrates

● In-container sterilized milk concentrates are prepared from UF skim milk.

● Such concentrates with edible carbohydrates have TS of 40 % and shelf life over 1 year.

8. Sweetened condensed milk

● UF concentrates are used in making of SCM. Such product has reduced sandiness in the texture.

9. Ice – cream

● UF can be used to prepare ice cream by using UF skim milk or UF reconstituted skim milk. Ice cream doesn’t shows any change in viscosity, specific gravity and overrun but gives improved creamy body and texture.

10. Non – fat dairy coffee whiteners

● Retentates obtained by UF of skim milk are freeze – dried. The product is comparable to commercial non – dairy coffee creamer and has acceptable dispersibility.

11. Whey protein quarg

● Concentrate obtained by UF of mixture of 80 % whey and 20 % skim milk is heated to obtain firm coagulum. It is also suitable for sweet desserts and puddings.